Center for Pulsed Power and Power Electronics.
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Conference Paper/Presentations

Publication Year:  2022
+ Pv To Vehicle, Pv To Grid, Vehicle To Grid, And Grid To Vehicle Micro Grid System Using Level Three Charging Station
  A. Balal; M. Giesselmann
Abstract:  This paper makes use of electric vehicles (EVs) that are simultaneously connected to the Photovoltaic Cells (PV) and the power grid. In micro-grids, batteries of the electric vehicles (EVs) used as a source of power to feed the power grid in the peak demands of electricity. EVs can help regulation of the power grid by storing excess solar energy and returning it to the grid during high demand hours. This paper proposes a new architecture of micro-grids by using a rooftop solar system, Battery Electric Vehicles (BEVs), grid connected inverters, a boost converter, a bidirectional half-bridge converter, output filter, including L, LC, or LCL, and transformers. The main parts of this micro-grid are illustrated and modeled, as well as a simulation of their operation. In addition, simulation results explore the charging and discharging scenarios of the BEVs.

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Publication Year:  2021
+ A Case Study For Connecting Bidirectional Pev Station For Reactive Power Support To The Gleamm Prototype Microgrid
  S. Daneshvardehnavi; C. A. Negri; K. E. K. Schmitt; S. Bayne; M. Giesselmann
Abstract:  This paper presents a control strategy for reactive power support using Plug-in Electric Vehicles (PEV) as a case study for the Global Laboratory for Energy Asset Management and Manufacturing (GLEAMM) microgrid. The control topology is divided into two levels with a dynamic limitation. This Electric Vehicle (EV) station Charger has a topology including a full-bridge AC-DC rectifier and a bidirectional half-bridge DC-DC converter. In the first level, a PQ and power control are used for the AC/DC inverter and DC/DC converters, receiving the set-points for active and reactive power from the upper level. The second level is a central controller that is used to manage the reactive power at the microgrid and to provide the necessary power setpoints for the PEV. A dynamic limitation strategy is proposed to maximize the reactive power support maintaining a reasonable amount of active power to charge the EV battery, considering the maximum limitation of the AC/DC inverter. To validate the effectiveness of the proposed control strategy, simulation results from a three-phase system are simulated in Matlab/Simulink environment.

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+ A Dynamic Load Control Strategy For An Efficient Building Demand Response
  K. E. K. Schmitt; I. Osman; R. Bhatta; M. Murshed; M. Chamana; S. Bayne
Abstract:  This paper proposes a computationally efficient building energy management algorithm for demand response that can serve as a grid-ancillary system. The controller aims to regulate flexible loads and intelligent switches, complying with the utility"™s request. The control algorithm dynamically optimizes the load"™s configuration of the building. This optimization is based on the required power consumption level and the resident"™s actual comfort constraints. Since the load-matrix considered by the proposed algorithm is computationally expensive, a novel region-selection approach is incorporated in the algorithm to make the strategy computationally efficient. The proposed algorithm is validated through OPAL-RT Real-Time Digital Simulation with Raspberry Pi. The test results show that the algorithm is capable of curtailing controllable loads during emergencies and outage scenarios to maintain an uninterrupted supply to the critical loads and respect the power limit request of the building.

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+ A Multi-Term Boltzmann Equation Toolset For Low Temperature Plasmas
  M. Flynn; A. Neuber; J. Stephens
Abstract:  Low temperature plasma (LTP) models, such as fluid and global models, frequently rely on Boltzmann equation (BE) solvers for the fast calculation of rate and transport coefficients from cross section data. While multi-term BE solvers currently see strong support in the kinetic modeling community, two-term BE solvers remain the preferred choice in the greater pulsed power and plasma science community. The limitations of the two-term approximation are well known, yet it is still regularly assumed that the two-term approximation is suitable for applications in LTP models. Recent studies have demonstrated otherwise where, even in a simple 1D fluid model, the use of multi-term derived rate and transport coefficients yielded superior fluid model results compared to the same model using two-term derived rate and transport coefficients.Much of the reluctance in adopting multi-term BE solvers may be attributed to a lack of publicly available tools. Here, we report on the public release of MultiBolt v3.0.0 as a free and open-source C++ header library as well as its pre-compiled terminal-based executable and graphical user interface. We also report on the inclusion of new functionality in temperature dependence, superelastic collisions, and the object-oriented treatment of both discrete and analytic cross sections.

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+ Demand Side Management And Economic Analysis Using Battery Storage System (Bss) And Solar Energy
  A. Balal; M. Giesselmann
Abstract:  Shortage of power generation results in unplanned load shedding. Active participation of the people on the demand side provides a solution by moving loads from peak time to off/peak hours during the day. This paper presents a Demand Side Management (DSM) that includes a rooftop photovoltaic system, a Battery Storage System (BSS), a hybrid control system, and a grid-tie inverter to reduce peak demands. The hybrid controller ensures that the maximum solar power generated is used or stored in the batteries for a given load, and any excess energy feeds the power grid. In this system, essential loads and generated power from rooftop PV systems are constantly monitored, and power generated by solar panels is preferred above grid electricity. According to the results, this system provides 100 % of each residence"™s required energy, plus an annual 6497 kWh to feed the AC grid and store in the BSS, resulting in monthly cost savings and the elimination of peak loads, particularly during the summer months, as well as a variety of environmental benefits.

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+ Effect Of Humidity On Charge Decay In Varying Atmospheric Gases
  Z. Cardenas; B. Esser; I. Aponte; J. Dickens; J. Mankowski; J. Stephens; D. Friesen; C. Nelson; N. Koone; D. Hattz; A. Neuber
Abstract:  Characterization of surface charge decay for varying materials "“ PTFE, Acrylic, and metals "“ of 100 mm diameter, radially symmetric bodies was performed. In a gaseous environment, charged materials will lose their charge depending on gas type, humidity, and other environmental factors. Eventually, the charge will be (1) neutralized by ions or electrons in the surrounding gas (2) distributed by conduction on the material surface or in its volume (3) or neutralized by ions or electrons in the material surface and volume. Metal and polymer samples are charged to a known potential in the tens of kilovolts range, and the decaying voltage is monitored with a non-contact probe until the potential reaches near zero. Humidity has an impact on both groups of materials. As a baseline, in air at 42% relative humidity in an enclosed chamber, a positive charge equivalent to 20 kV potential on a metal sphere of 50 mm radius decays to near zero within 25 minutes. In contrast, the same sphere negatively charged decays slightly faster within 20 minutes. Overall, the humidity has a significant effect on the charge decay time, such that an order of magnitude longer times (hours) are observed at low humidity. Effects of chamber size were also studied, drawing a connection to charge carriers in the air available for decay, with chambers of volume(s): 3.3 105 cm3 and 1.4 106 cm3, respectively.

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+ Enhanced Performance Of Metamaterials Loaded Substrate Integrated Waveguide Antenna For Multiband Application
  Rawat, A; Tiwari, A; Gour, S; Joshi, R
Abstract:  The investigation of the design and analysis of a Metamaterials loaded Substrate Integrated Waveguide (SIW) antenna for Multiband Applications. A ground arrangement through a radiating rectangular patch conflicting the feed line as well as a mixture of Substrate Integrated Waveguide and Metamaterials is presented for the proposed antenna. These are utilized to improve the antenna's bandwidth and Radiation pattern while also reducing its size. To improve directivity, gain, and bandwidth, a complementary square split ring resonator and Substrate Integrated Waveguide are utilized. The proposed antenna structure is made of FR-4 epoxy with a epsilon(r)=4.4. The antenna functions over the frequency range of 6-18 GHz, with a resonant frequency for Wireless LAN and WIMAX.
+ Hierarchical Operation Of Flexible Building Microgrids For Distributed Critical Loads Resiliency
  M. Chamana; K. Schmitt; R. Bhatta; I. Osman; S. Liyanage; M. Murshed; S. Bayne; J. MacFie
Abstract:  Community-scale microgrids play an essential role in serving critical loads during emergency conditions, involving the operation of breakers, tie-switches, distributed energy resources (DERs), and loads. Electric loads are primarily considered as lumped loads without many granular levels of controls. Flexible buildings offer the central microgrid management system an opportunity to shed multiple noncritical loads at granular levels by adopting Internet-of- Things (IoT) based controls. This work presents a novel bi-level optimal sequence of operations for managing the controllable devices in microgrids to serve loads, based on a priority scheme in community scale-scale microgrids. The proposed methodology is formulated as a mixed-integer linear programming (MILP) model and adapts to various operating conditions. The proposed method is validated through case studies that are performed on the Banshee microgrid benchmark model.

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+ High-Voltage Silicon Carbide Thyristors On N-Doped Epi For Pulsed Power
  H. O"™Brien; A. Ogunniyi; S. -H. Ryu; T. Tsoi; S. B. Bayne
Abstract:  The Army Research Laboratory (ARL) has funded the development of high-voltage silicon carbide (SiC) thyristors and diodes for pulsed power switching, culminating in the novel 1.0 cm2, 15-kV SiC thyristor with n-type doping in the drift layer. N-type thyristors have been predicted to achieve faster switching speeds and lower switching losses, but were only recently realized following the development of novel fabrication techniques. These devices are targeted to reduce volume and increase reliability of pulsed switches in high-energy systems. ARL and Texas Tech University characterized the first fabrication lot of these devices for high-voltage DC-blocking capability (<1 µA leakage at 15 kV), optimal turn-on controls (4 A gate pulse), and on-state resistance at high current densities (up to 3 kA/cm2). This paper presents recent analysis of the turn-on speed and dI/dt capability for low-kHz pulse repetition of the n-type SiC thyristors as compared to previously reported 15-kV p-doped SiC thyristors. The current through the n-thyristor peaks 50 ns earlier, reaches 10% higher amplitude, and has significantly faster dI/dt as compared to the similarly designed p-thyristor.

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+ Intrusion Detection From Synchrophasor Data Propagation Using Cyber Physical Platform
  V. Roy; S. S. Noureen; S. Atique; S. Bayne; M. Giesselmann
Abstract:  Some of the recent reports show that Power Grid is a target of attack and gradually the need for understanding the security of Grid network is getting a prime focus. The Department of Homeland Security has imposed focus on Cyber Threats on Power Grid in their "Cyber Security Strategy,2018" [1] . DHS has focused on innovations to manage risk attacks on Power System based national resources. Power Grid is a cyber physical system which consists of power flow and data transmission. The important part of a microgrid is the two-way power flow which makes the system complex on monitoring and control. In this paper, we have tried to study different types of attacks which change the data propagation of Synchrophasor, network communication interruption behavior and find the data propagation scenario due to attack. The focus of the paper is to develop a platform for Synchrophasor based data network attack study which is a part of Microgrid design. Different types of intrusion models were studied to observe change in Synchrophasor data pattern which will help for further prediction to improve Microgrid resiliency for different types of cyber-attack.

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+ Investigating The Effects Of Non-Linear Loads On Generator Sets
  J. A. Rodriguez; F. Salcedo; S. B. Bayne
Abstract:  Non-linear loads have become more prevalent due to the increasing use of power electronics for power conditioning and regulation. The current harmonics generated from non-linear loads can cause long-term effects on generator sets, such as the degradation of their lifetime due to higher operating temperatures and component failures due to high current transients. A testbed was developed to run a 3-kW military tactical generator set under non-linear loads. The 3-kW generator set includes a permanent magnet alternator (PMA) and a power electronic converter to deliver a 120VAC/240VAC output at 60 Hz. A range of non-linear loads was developed to create several load profiles for the generator set. The generator set was tested in four-hour and two-hour intervals for several weeks under different load profiles to stress its alternator and internal power electronics. In addition, several measurements were taken during testing, such as the output power, output voltage and current, and stator winding temperature. The collected data and testing suggest that the power electronics converter is more susceptible to the current harmonics than the PMA. These issues can result in premature failures and overall degradation of the lifetime of the generator set.

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+ Maximum Power Point Tracking Of Inductive Resonant Wireless Power Transfer Systems Using A Buck Converter On The Receiving Side To Mitigate The Effects Of Coil Misalignment
  A. V. Bilbao; S. B. Bayne
Abstract:  The purpose of this paper is to show the results obtained by performing maximum power transfer in inductive resonant wireless power transfer (WPT) systems. The research highlights the importance of power electronic systems on the receiving side of a WPT system. Before getting into the specifics of the research, a fundamental theoretical analysis about WPT systems is performed followed by an LTSpice simulation setup and results. The results presented show that power electronic DC/DC converters can be successfully used to increase the amount of wirelessly delivered power through impedance matching.

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+ Rapid Capacitor Charger With Advanced Digital Control
  M. Giesselmann; J. Mayes
Abstract:  We are reporting on the design of a compact capacitor charger with a rated output voltage of 50kV and a power rating of 10kJ/s. The input source is a 208V, 3-phase AC utility supply. The charger shall fit in to an 19inch, 5U enclosure. The core of the charger is a HV-power pack containing a high-frequency transformer with a nano-crystalline core, multiple output windings using litz-wire and integrated HV rectifiers. The primary of the transformer is driven by an H-bridge inverter with advanced IGBTs and matching High Power Drivers. The control is through a state-of-the-art Digital Signal Controller (DSC) with fast cycle-by-cycle Peak current mode control, leading edge blanking, and high resolution, fast, automated slope compensation for current loop stability. The DSC runs at 5 times the speed of the main processor core for ns level PWM resolution.

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+ Reliability Of Sic Mps Diodes Under Non-Repetitive Forward Surge Current
  T. Tsoi; B. Westmoreland; S. Bayne; S. Jadva
Abstract:  Silicon Carbide (SiC) Merged PiN-Schottky (MPS) diodes have the benefit of conduction modulation under high current events while achieving low forward voltage and zero reverse-recovery under normal operations. Thus, the SiC MPS diodes can sustain surge currents several times larger than their average current rating, avoiding oversizing components and resulting in a more compact power electronic device. Two SiC MPS diodes were evaluated using a non-repetitive surge current testbed that delivers a square current pulse of 800 A. Five devices from each group were subjected to a ten µs current pulse every 20 seconds. The first device from each group started at lower current levels and was increased until device degradation occurred. Subsequent devices were then tested at the highest current level until degradation. Both groups have sustained currents up to 2.5 times their rated surge current rating. These devices were subjected to several thousand pulses, and their electrical characteristics, such as forward IV and reverse blocking voltage, were measured between testing intervals. Device degradation was observed as the reverse-blocking voltage has significantly decreased from preliminary measurements, but no degradation of the forward-IV curve was observed. The collected data demonstrate the device"™s ability to operate under non-repetitive surge current events. Each device has sustained several hundred pulses above their rated surge current rating before any sign of degradation was detected. Device degradation becomes apparent when the leakage current increases as the MPS diode is blocking voltage. They eventually become prone to short-circuit failure due to a reduced reverse blocking voltage capability.

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+ Safe And Intelligent Wireless Power Transfer System
  D. Z. Graves; A. V. Bilbao; S. B. Bayne
Abstract:  The purpose of this paper is to show the results obtained from novel research performed in the area of inductive-resonant wireless power transfer (WPT) safety. Traditionally a communication link between the transmitter and receiver power electronic system is required to ensure that power is delivered only to a suitable target system. This research aims to eliminate the communication hardware required to increase the system"™s volumetric power density and mass. Machine learning is used to perform current waveform analysis to detect the receiver"™s signature and enhance system safety.

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+ Sensitivity Of Pbx 9501 And Pbx 9502 To Milling Operations
  J. Williams; E. Weeks; R. Clark; S. Watkins; J. Dickens; J. Mankowski; J. Brinkman; A. Neuber
Abstract:  Explosive driven pulsed power performance benefits from modern polymer-bonded explosives. In practical application, high precision in the dimensional shape is required, and high machining speeds are desired. The limits of machining speed, driven mainly by the thermal response of the energetic material, are investigated. Specifically, the thermal response of PBX 9501 (95% HMX, 2.5% Estane, 2.5% BDNPA/BDNPF by weight) and PBX 9502 (95% TATB, 5% Kel F-800 by weight) under conventional milling methods is examined. The presented work focuses on face milling performed with dry machining on a CNC, remote-controlled milling machine. The primary parameters of interest are the spindle speed, feed rate, step size, and depth of cut, with additional consideration given to endmill diameter, milling technique, and the number of flutes. The temperature of the system is monitored via high-speed IR videography and near the cutting interface with a K-type thermocouple inserted into the endmill"™s through-coolant hole. Operational forces and torques are recorded by a 6-axis force sensor mounted beneath the HE samples.An empirical relationship between temperature and the milling parameters is presented. Overall, milling regimes exist outside of DOE-STD-1212-2019 for which milling temperatures remain well below the HE critical temperatures.

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+ Sic Gtos Thyristor For Long Term Reliability On Pulsed Power Application Test
  T. Tsoi; C. Whitworth; M. Kim; S. Bayne; H. O"™Brien; A. Ogunniyi
Abstract:  Silicon Carbide (SiC) is a wide-bandgap semiconductor with a wider bandgap, higher critical electric field, higher saturation velocity, and higher thermal conductivity than silicon, making it desirable for pulsed power applications. The n-type Gate Turn-off thyristor (nGTO) is a controllable solid-state switch with high blocking voltage and high current conduction capabilities. However, its device structure is challenging to develop using SiC. Wolfspeed has developed a 15.0 kV SiC nGTO that withstood peak current up to 1.0 kA. A testbed was developed to evaluate the long-term reliability of these SiC nGTOs. The pulser operates with a capacitor bank charged to 10.0 kV to deliver a 35.0 µs ring-down current waveform through the device. The SiC nGTOs were pulsed with a repetition rate of 0.5 Hz. It was observed that the device dissipated 700.0 J peak energy during pulsing. COMSOL Multiphysics simulated the SiC nGTO during a single pulsing event. The simulation models the thermal flow and current density in the nGTO. The thermal result shows the peak device temperature rising to 360.1 K after 17 µs into the pulsing event. The peak magnitude of current density reached 15 kA/cm2

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+ Surface Charge Distribution Mapping Using An Electrostatic Probe
  M. LaPointe; B. Esser; I. Aponte; Z. Cardenas; J. Dickens; J. Mankowski; J. Stephens; D. Friesen; C. Nelson; N. Koone; D. Hattz; A. Neuber
Abstract:  Undesired accumulation of charge on dielectric materials causing electrostatic discharges can be an issue in pulsed power systems and electrical systems in general. As such, an understanding of surface charge distribution, charge accumulation, and decay is required. An in-house no-contact electrostatic probe designed with a 2 mm resolution was fabricated to measure and map surface charge distribution. Designed as a contactless instrument, the probe consisting of a metal rod and low leakage amplifier circuit probes the electric potential near the surface. A scan of the surface then provides the raw data, a potential distribution. The actual probe response - i.e., the surface charge to voltage transfer function, is accounted for in post-processing. This is accomplished via an Inverse Wien Filter - a technique often applied in image processing - to deconvolve the probe response from the measured data. A commercially available electrostatic probe, the Trek 341B meter with a 3455ET probe, capable of measuring +/- 20 kV was compared to the in-house probe that is designed to cover a wider range from +/- 35 kV. A resolution better than the simple probe resolution is achieved through the distribution"™s scanning voltage method and deconvolution. Applying repeated scans, surface charge decay was tracked on various polymer materials to determine the material and environment dependence; materials included were PA6, PTFE, and others. As an example of material dependence, samples charged to 20 kV at 65% humidity experience full charge decay in approximately 45 seconds for PA5 (152 mm dia.), while it took about 100 times longer for PTFE (51 mm dia.) to observe the same decay/redistribution of charge.

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+ Temporally Resolved Light Emission And Optical Emission Spectroscopy Of Surface Flashover In Vacuum
  R. Clark; J. Young; W. Brooks; M. Hopkins; J. Mankowski; J. Stephens; A. Neuber
Abstract:  Early light emission provides information about the dominant mechanisms culminating in vacuum surface flashover (anode-initiated vs. cathode-initiated) for particular geometries. From experimental evidence gathered elsewhere, for the case of an insulator oriented at 45° with respect to the anode, anode-initiated flashover is believed to dominate since the field at the anode triple point is roughly three times that of the cathode. Similar to previous work performed on cathode-initiated flashover, light emission from the voltage rise through the impedance collapse is collected into two optical fibers focused on light emanating from the insulator in regions near the anode and cathode. The optical fibers are either connected to PMTs for spectrally integrated localized light intensity information or to a spectrograph used in conjunction with an ICCD camera. Challenges associated with localizing the flashover for optical diagnostics and incorporating the optical diagnostics into the high-field environment are discussed. Initial results for cross-linked polystyrene (Rexolite 1422) support the premise that flashover is initiated from the anode for these geometries, as early light from the anode leads cathode light up to photocathode saturation. Early spectroscopy results show promise for future characterization of the spatio-temporal development of emission from desorbed gas species across the insulator surface and identification of bulk insulator involvement if it occurs.

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Publication Year:  2020
+ A Review On Reliability Of Microgrid
  S. Ramabhotla; S. B. Bayne
Abstract:  Microgrid is considered as the future power systems due to the demand in the power supply and also due to its capability of integrating with the renewable energy sources. Based on the demand and location, the microgrid operates independently in an islanded mode by disconnecting from the power grid. A microgrid improves the efficiency of power consumption, along with the reliability of the power quality and power supply. The reliability of the microgrid is an important aspect to improve for the efficient power quality and availability of the electricity. This paper provides a review on reliability of microgrid considering various techniques and methods. The paper discusses about the background and concept of microgrid, effect of reliability in power systems, different scenarios of reliability in microgrids. Also, the challenges and solutions are elaborated from the implementation of various optimization techniques for the microgrid systems.

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+ A Study On The Contributing Factors Of Rf Breakdown In Atmospheric Air
  I. A. Aponte; B. Esser; J. C. Dickens; J. J. Mankowski; A. A. Neuber
Abstract:  DC and RF breakdown at 3.3 MHz was studied in centimeter size gaps - 1 - 10 mm "“ with comparison to small gaps in literature and Monte Carlo simulations in atmospheric conditions. As a point of reference, DC breakdown using stainless-steel Bruce-profile electrodes were measured to compare with RF measurements. RF breakdown with a slow rising envelope ($\sim 5\ \text{mV}/\mu\mathrm{s}$) yielded approximately 80% of DC measurements (~25 kV/cm in 5 mm gap), which agrees with Monte Carlo simulations and results found in literature. Increasing the envelope rise time to greater than $1000\ \mathrm{V}/\mu \mathrm{s}$ yielded ~120% of DC measurements (~37 kV/cm in 5 mm gap). Comparisons with Monte Carlo simulations which included photon processes "“ theorized to be critical to obtaining accurate results "“ furthered understanding of the processes involved in pre-ionization before breakdown occurs.

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+ Analysis Of Experimental Multipactor Observation Signals Using Spark3D Software
  T. Sugai; Z. Shaw; J. Dickens; A. Neuber
Abstract:  Multipactor is a resonant nonlinear electron multiplication effect that may occur in high power microwave devices at very low pressures, such as those operating in particle accelerators and satellite subsystems. Its effects range from signal degradation to the damage and destruction of microwave components. Thus, multipactor physics has been studied through theoretical analysis, numerical simulation, and experiment. Previously, we developed a direct electron observation system using an Electron Multiplier Tube (EMT) and succeeded to directly detect multipactoring electrons in the center of the broadwall of rectangular waveguides 1, 2. Here, we provide a method for evaluating the electric charge density and secondary emission yield (SEY) in waveguides. The experimentally obtained EMT signal is analyzed with the extensive usage of the numerical simulation software Spark3D. The software was utilized to analyze multipactor onset in waveguide structures, where the electric field distribution without multipactor was carefully simulated, employing high-frequency solvers. The EMT signal and the charge density were simulated for the same conditions as the experiment. As a result, a calibration line indicating the proportional relation between the EMT voltage and the charge density, which is independent of some conditions, i.e., input power and gap size, was obtained. Further, after adjusting the SEY curve imported to Spark3D, the rising shape of the experimental EMT signal pulses fit with the simulated one, and the experimental threshold power for the EMT signal generation was consistent with the simulated multipactor threshold power. Since the simulation matches the experiment in threshold power and signal shape, one expects that the charge density and SEY curve deduced from the simulation are accurate.

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+ Application Of Synchronous Condensers For Enhanced Resilience Of A Renewable Energy Dominated Electric Grid
  S. Basu; V. Roy; M. Giesselmann
Abstract:  The extensive integration of renewable sources of energy has caused the number of conventional power plants to go down. This in turn causes a reduction of the system resilience, i.e. the ability of a system to recover from a fault. Synchronous condensers, when included in the grid, contribute to the fault current and provide voltage support thereby enhancing dynamic voltage recovery. This article summarizes the capacity of a synchronous condenser, when connected to the power grid with wind or solar power plants to compensate for reactive power compensation and injection of active power at their point of common coupling. A case, based on a local distribution network, is developed on a 33kV transmission line that feeds into several inductive loads. Simulations are performed in PSIM to display the enhancement of system stability and reduction in power losses while supplying reactive power by activating synchronous condensers to the grid with given practical grid rules.

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+ Electric Wheelchair-Humanoid Robot Collaboration For Clothing Assistance Of The Elderly
  R. P. Joshi; J. P. Tarapure; T. Shibata
Abstract:  In rapidly aging societies, robotic solutions for clothing assistance can significantly improve the quality of life of the elderly while coping with the shortage of caregivers. Previously, we proposed a framework for the same by employing imitation learning from a human demonstration to a compliant dual-arm robot. As the robot has a limited workspace, this framework involves a manual movement of the wheeled chair by pushing it while coordinating with the robot to stay within the workspace of the robot [1]. To avoid the manual push and coordination, we facilitate the automatic movement of the chair based on the trajectory of the robot's dual arms. In this paper, we present an approach for the collaboration of an electric wheelchair and a humanoid robot to achieve the clothing assistance task. Our approach incorporates Manifold Relevance Determination (MRD) to learn an offline latent model from the simultaneous observations of the clothing assistance task as well as the movement of the wheelchair. We trained and tested the latent model on different human subjects by dressing a sleeveless T-shirt. Experimental results verify the plausibility of our approach. To the best of our knowledge, this is the first work addressing collaboration between wheelchair and robot to perform clothing assistance.

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+ Experimental Demonstration Of A W-Band Photonic Bandgap Klystron
  J. Stephens; G. Rosenzweig; J. Tucek; K. Kreischer; M. Shapiro; R. Temkin
Abstract:  This paper details recent progress on the experimental demonstration of a W-band klystron amplifier completed at the MIT. The amplifier utilizes a square lattice photonic bandgap (PBG) structure that permits the use of a highly oversized beam tunnel of diameter ~λ/4. Cold test measurements of the PBG klystron cavities revealed successful fabrication of the device. In hot test, a small-signal gain of 26 dB was measured at 93.7 GHz, with a saturated output power of 30 W.

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+ High Power 2.85 Ghz Gan Rf Source For Direct Detection Of Multipactor Research
  B. Esser; Z. Shaw; J. C. Dickens; A. A. Neuber
Abstract:  A pulsed 2.85 GHz RF source design with high average power is presented for use as the principle exciter in an experiment to directly detect multipactor. With a rated output power of 700 W each in long pulse mode (~ 100 â–¡s), four Cree GaN HEMTs are used to achieve a maximum of 2.8 kW rated output. A fifth HEMT is used to drive the four output devices with approximately 40 W each. A free running VCO with low tuning sensitivity is used which ensures a stable frequency output despite a noisy environment. Buffering and initial amplification is provided by an LNA with a TTL RF switch used to generate the pulses. With a rise time of 35 ns, this switch is fast enough to create reasonably square pulse edges. A microwave amplifier with 45 dB of gain provides the majority of the gain in the system and the power necessary for the final GaN stages, approximately 9 W. An in-line micrometer adjusted, continuously variable attenuator between LNA and TTL switch provides level control.

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+ Large-Scale Adoption Of Self-Synchronized Universal Droop Controller-Based Inverters To Enable Ancillary Services For Different Modes Of Distribution System Operations
  L. Arce; M. Chamana; I. Osman; B. Ren; Q. -C. Zhong; S. Bayne
Abstract:  This work proposes the large-scale adoption of self-synchronized universal droop controller (SUDC)-based inverters to enable ancillary services for different modes of distribution system operations. The IEEE 123 bus system was modeled on a real-time simulator to study the performance of large-scale adoption of SUDC inverters in a distribution system. The resulting data collected shows that the voltage and the frequency were regulated within ranges, such as less than 5% for voltage and less than 0.5% for frequency, under different load variations and grid operations. Also, the black start was achieved within 0.4 s without any voltage overshoot. Through the simulation and validation on a small microgrid and the IEEE 123 bus distribution system, it can be concluded that the SUDC was successfully adopted to regulate the voltage and the frequency within the given ranges, and black start achieved within 1 s without voltage overshoot for different modes of distribution system operations.

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+ Lt-Spice Model For Induction Generators With Self-Excitation
  M. Giesselmann; S. Daneshvardehnavi
Abstract:  We are presenting an LT-Spice Model for 3-phase Induction Generators that are operating in off-grid mode using a 3-phase capacitor bank for self-excitation. To model the self-excitation, we include the effects of a non-linear magnetizing inductance with residual magnetic flux and saturation. Our model represents both the electrical as well as the mechanical characteristics of the machine.

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+ Multipactor Thresholds In A Planar Test Cell
  Z. C. Shaw; B. Esser; J. C. Dickens; J. J. Mankowski; A. A. Neuber
Abstract:  A planar test cell was designed and implemented to observe the multipactor effect in waveguide structures. This plug and play device allows for multiple geometries to be machined and easily replaced within the test structure. A direct detection method was used to observe the multipactor effect while the upper and lower thresholds were measured for a 2.1 mm gap at 2.85 GHz. While there is an obvious lower limit to multipactor (2 kW), there was no observable upper limit even at powers over 200 kW. This is attributed to the transverse electric field distribution in the dominant TE10 mode which is not taken into account in most multipactor theoretical models.

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+ Regional Wind Power Ramp Forecasting Through Multinomial Logistic Regression
  Chen, XM; Zhao, J; He, M
Abstract:  Wind power ramps are the abrupt yet significant change in wind power productions. The information on the ordinal levels of impending wind power ramp could help power system operator to arm operation or ramping reserves in a timely manner. This paper presents novel approaches for regional wind power ramp level forecasting using real-time meso-scale wind speed measurements. Motivated by the correlation of the meso-scale wind speed measurements with the regional wind power data, the proposed approach utilizes multinomial logistic regression for wind power ramp forecasting. An approach that combines the probabilistic output of individual regressive models in a weighted manner is proposed, with the weights calculated by minimizing the Brier skill score of the combined model. The proposed methods are tested by using real-world data, and is compared with benchmark methods. The results reveal the effectiveness of the proposed approaches.
+ Self-Adjusting Inertia Emulation Control In V2G Application
  Dinkhah, S; He, M
Abstract:  in this paper, we propose an improved control mechanism for a microgrid. This happens through adding a controlling measure and algorithm one step ahead of the combination of inertia emulation control technique and droop control. This controlling step is a self-adjusting control system designed for a stable electrical grid model. This control technique applied to a home that is furnished with Photo-voltaic (PV) system and Vehicle to Grid (V2G) capable Electric Vehicle (EV). This control could run in both grid-connected and islanded modes in a microgrid application. The model is used to achieve an improvement in frequency over the standard droop/inertia emulation control method, in case of load changes and faults. The provided control system can handle different scenarios such as sudden load changes and transient conditions through dealing with the power of the battery and PV to regulate the voltage and frequency in this microgrid system. This control technique will achieve a better result compared to the standard control technique. Both models are implemented in MATLAB/Simulink. The results for the simulations are presented, showing the improvements over the fixed values of the controller.
+ Time Series Forecasting Of Total Daily Solar Energy Generation: A Comparative Analysis Between Arima And Machine Learning Techniques
  S. Atique; S. Noureen; V. Roy; S. Bayne; J. Macfie
Abstract:  In this paper, the potential of machine learning based methods for time series forecasting of total daily solar energy generation has been explored. Firstly, the time series is modeled using the seasonal version of well known classical method auto regressive integrated moving average (ARIMA) and its performance is later compared to two other popular machine learning methods, support vector machine (SVM) and artificial neural network (ANN). The potential of machine learning based methods in this line of work is demonstrated by the superior performance of SVM. However, the reasons behind the low yield of ANN need to be inspected to enhance our understanding. In spite of SVM's relative success in prediction of solar generation, the overall accuracy still needs to be improved and the methods to achieve this objective should be researched in future.

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Publication Year:  2019
+ A Flexible Poisoning Attack Against Machine Learning
  Jiang, WB; Li, HW; Liu, S; Ren, YZ; He, M
Abstract:  Recent years have witnessed tremendous academic efforts and industry growth in machine learning. The security of machine learning has become increasingly prominent. Poisoning attack is one of the most relevant security threats to machine learning which focuses on polluting the training data that machine learning needs during the training process. Specifically, the attacker blends crafted poisoning samples into training data in order to make the learned model beneficial to him. To the best of our knowledge, existing researches about poisoning attack focused on either integrity attack or availability attack, which did not unify these two attacks together. Aside from that, from the attacker's perspective, attacker's strategy is not flexible enough. Finally, existing proposals only concentrated on increasing the test error of the learned model but ignored the importance of the concealment of attack. To overcome these issues, we firstly present a thorough adversarial model for poisoning attack in which attacker's strategy is defined from two aspects, i.e., the effect of attack and the concealment of attack. Then we unify integrity attack and availability attack together in similar formulations. Furthermore, in order to enhance flexibility, a tradeoff parameter is inserted into attacker's objective function which means the attacker can balance the attraction of effect against the requirement of concealment. Finally, as examples, extensive experiments are conducted on linear regression and logistic regression to demonstrate the effectiveness of attack.
+ Analysis And Application Of Seasonal Arima Model In Energy Demand Forecasting: A Case Study Of Small Scale Agricultural Load
  S. Noureen; S. Atique; V. Roy; S. Bayne
Abstract:  This paper has presented the use of Auto Regressive Integrated Moving Average (ARIMA) method for forecasting of seasonal time series data. The dataset that has been used for modeling and forecasting is a small-scale agricultural load. ARIMA method can be applied only when the time series data is stationary. As seasonal variations make a time series non-stationary, this paper also presents analyses on testing stationarity and transforming non-stationarity into stationarity. Lastly, model has been developed with a specific selection of orders for autoregressive terms, moving average terms, differencing and seasonality and the forecasting performance has been tested and compared with the actual value. The results are encouraging, however there is scope of further research in refining the idea.

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+ Anomaly Detection In Cyber-Physical System Using Logistic Regression Analysis
  S. S. Noureen; S. B. Bayne; E. Shaffer; D. Porschet; M. Berman
Abstract:  The emerging smart grid, cyber-physical infrastructure, provides a steady, secure, and reliable power system over the current power grid. Synchrophasor systems, like Phasor Measurement Units (PMUs), are a key element of smart grids. They have the capability to measure time-coherent phasors of a grid. The key advantage of PMUs is the fast sampling rate that they provide over traditional Supervisory control and data acquisition (SCADA) systems which can be in the range of 30-120 samples/second. These higher sampling rates come at the cost of higher data quantities. Generating large amounts of data per day poses a challenge in making the most efficient use of information. In this paper, this problem has been addressed utilizing machine learning techniques, Logistic Regression Analysis, on PMU data. Identifying system anomalies in smart power grids is the primary focus of this paper. The standard IEEE 39 Bus system has been modified using the RT-LAB environment to generate faults and to produce synthetic synchrophasor data. Archived/offline mode data from a Phasor data concentrator (PDC) database is being used to train and test the algorithm. Additionally, the algorithm has been tested in real-time using an OPAL-RT digital real-time simulator.

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+ Course Development On Synchrophasor Applications At The Undergraduate And Graduate Levels
  M. Chamana; S. Bayne; A. Swift
Abstract:  Phasor Measurement Unit (PMU) design and application requires knowledge of various mathematical and electrical engineering fundamentals. The fundamental theories are covered in lower level courses offered at the undergraduate level in a typical electrical engineering and energy related curriculum. Furthermore, laboratory equipment/device based courses help students to improve their practical skills. Since students find experimental, product development and group work related courses more engaging, they are motivated to enroll in such courses. This paper summarizes a PMU design and application course suitable for electrical engineering/renewable energy undergraduate and graduate students. The paper is aimed towards helping course developers who plan to develop similar courses in the future.

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+ Design,Development And Experimental Setup Of A Pmu Network For Monitoring And Anomaly Detection
  V. Roy; S. Noureen; T. Atique; S. Bayne; M. Giesselmann; A. S. Subburaj; M. A. Harral
Abstract:  Introduction of Synchronized phasor measurement unit (PMU) in power system is a solution for monitoring system wide disturbances. PMUs provide precise information about a system's phasors such as magnitude and phase angle of sine waves of the system. PMU data is a valuable source when determining the post-mortem of a fault, or a system disturbance. It can be unveiled what time the system began to falter and exactly what instabilities the system experienced. Knowing the cause of such instabilities will allow enhancement of the current system protection system. This will help in minimizing risk, disruptions or total system collapse. PMUs are synchronized via global positioning system (GPS). For wide area monitoring (WAM), synchronization of the PMUs allows for interconnected systems to be monitored simultaneously, giving real time records. This paper explores the impact of PMU in modern power system, deployment strategies of PMU network around Texas Tech University, importance of PMU data collected from the network, correlation of events by data analysis and focus on how the time stamped information is valuable for grid stability. The ongoing smart architecture of grid will increase dependency and importance on PMU based network in future.

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+ Detection Of Impending Ramp For Improved Wind Farm Power Forecasting
  Zhao, J; Chen, XM; He, M
Abstract:  Detection of impending front-induced ramp events is studied as a new class of change detection problem - change detection for multiple time series with spatial dependency. A critical step to ramp event detection is to capture the spatial dependency between neighbor turbines' power output. To this end, a graphical model is utilized to model the dependency of turbine-level ramp events. Then, change point detection is carried out for the time series of individual turbines' power output, by using the belief from neighbor turbines in the dependency graph. Once an impending ramp is detected, the magnitude of ramp is then forecasted by using current measurement data. A key observation is that due to the movement of front, the best predictors for individual turbines' power output vary across three different regions of the wind farm. With this insight, different predictive models are adopted for forecasting power output from each region. Through numerical experiments, the proposed detection-based wind power forecasting method is proven to outperform conventional methods for wind power ramps.
+ Dynamic Modeling Of Pulsed Alternators Using Ltspice
  C. Negri; S. Daneshvardehnavi; M. Giesselmann
Abstract:  We are reporting on the formulation and performance of dynamic models for Pulsed Alternators for LTspice. The models are modular and hierarchical and cover both the electrical and mechanical aspects of the electric machine including the mechanical torque, speed and inertia. The models also include the effects of the damper cage and the excitation winding to accurately represent the sub-transient and transient behavior. The models can also be used to represent synchronous generators in steady state operation. LTspice is a powerful, widely available software package that can be used to model Pulsed Power circuits. We are presenting the detailed models as well as results of the simulations.

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+ Electrical Equivalent Model Of Vanadium Redox Flow Battery
  Y. R. Challapuram; G. M. Quintero; S. B. Bayne; A. S. Subburaj; M. A. Harral
Abstract:  Grid-scale energy storage systems have become popular for the growth of hybrid renewable power systems. Due to design flexibility, low manufacturing costs for large scale, indefinite lifetime and recyclable electrolytes Vanadium redox flow batteries (VRFBs) are a promising energy storage technology. In this paper, an electrical equivalent model of VRFB which is present in Distributed Asset Research Testing (DART) facility in Texas is proposed. The VRFB is connected to a 3.6kW resistive load. The effect of flow rate and pump power losses has been considered in modeling the VRFB. A control method for State of Charge (SOC) estimation is also proposed as it plays an important role in over-charge/ discharge of VRFB. The entire work is simulated in Matlab/Simulink environment and the results obtained prove the efficient operation of VRFB.

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+ Forecasting Of Total Daily Solar Energy Generation Using Arima: A Case Study
  S. Atique; S. Noureen; V. Roy; V. Subburaj; S. Bayne; J. Macfie
Abstract:  In this paper, a well known statistical modeling method named ARIMA has been used to forecast the total daily solar energy generated by a solar panel located in a research facility. The beauty of the ARIMA model lies in its simplicity and it can only be applied to stationary time series. So our time series data, which is seasonal and non-stationary, is transformed into a stationary one for applying the ARIMA model. The model is developed using sophisticated statistical techniques. The optimum model is chosen and validated using Akaike information criterion (AIC) and residual sum of squares (SSE). Error analysis is done to demonstrate the efficiency of the proposed method. The accuracy of the developed model can be further increased, which is subject to future research.

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+ Performance Comparison Of Commercial Gan Hemt Under Repetitive Overcurrent Operations
  J. A. Rodriguez; M. Kim; S. B. Bayne; H. O'Brien; A. Ogunniyi
Abstract:  Gallium nitride (GaN) high-electron-mobility transistors (HEMT) are of great interest for pulsed power applications due to their proven capabilities in RF applications. With further advances in GaN power semiconductors, there's an interest in the evaluation of their performance under repetitive overcurrent operation in power electronics applications beyond the manufacturer's prescribed operating parameters. A GaN HEMT from two different vendors were evaluated in a pulsed ring down testbed at 475 V with a peak current above 80 A over a repetition rate of 138 Hz. The testbed employed a temperature chamber to adjust the case temperature of the device during testing. The devices' electrical characteristics, such as transconductance, forward I-V curve and reverse blocking voltage were measured throughout testing and have not shown significant degradation. The collected data from these measurements allowed a comparison of the devices' performance and shows their ability to handle transient overcurrent conditions commonly found in power semiconductor device applications.

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+ Pv Power Generation Credit Sharing Towards Sustainable Community Solar
  Chen, XM; Zhao, J; He, M
Abstract:  This paper present a new conceptual framework of PV power generation credit sharing by leveraging social tie in residential community to maximize the financial benefit of community solar programs. Social tie-driven credit sharing schemes for residential community is designed to manage the dynamic allocation of solar PV power production ratio and credit among community members, so as to avoid unnecessary devaluation of solar PV power production by electric utilities. Along this avenue, a community solar management system that incorporates and integrates social tie network and credit sharing schemes is then developed.
+ Quantitative Evaluation Of Clothing Assistance Using Whole-Body Robotic Simulator Of The Elderly
  R. P. Joshi; T. Shibata; K. Ogata; Y. Matsumoto
Abstract:  The recent demographic trend across developed nations shows a dramatic increase in the aging population, fallen fertility rates and a shortage of caregivers. Robotic solutions to clothing assistance can significantly improve the Activity of Daily Living (ADL) for the elderly and disabled. We have developed a clothing assistance robot using dual arms and conducted many successful demonstrations with healthy people. It was, however, impossible to systematically evaluate its performance because human arms are not visible due to occlusion from a shirt and robot during dressing. To address this problem, we propose to use another robot, Whole-Body Robotic Simulator of the Elderly that can mimic the posture and movement of the elderly persons during the dressing task. The dressing task is accomplished by utilizing Dynamic Movement Primitives (DMP) wherein the control points of DMP are determined by applying forward kinematics on the robotic simulator. The experimental results show the plausibility of our approach.

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+ V2G For Reliable Microgrid Operations: Voltage/Frequency Regulation With Virtual Inertia Emulation
  S. Dinkhah; C. A. Negri; M. He; S. B. Bayne
Abstract:  In this paper, we propose a stable electrical grid model, in which a home with a Photo-Voltaic (PV) system and Vehicle to Grid (V2G) capable Electric Vehicle (EV) can operate in both grid-connected and islanded modes. The model is used for studying load transients, power-sharing, and fault analysis. The implemented control system overcomes challenging situations such as load changing and transient conditions by managing the power of the battery and PV and regulating the voltage and frequency in the islanded mode. The Maximum Power Point Tracking (MPPT) is modified to include a feature for limiting the power in case of islanded mode and fully charged EV battery. Furthermore, the droop control and virtual inertia is utilized in a unified control manner. The model is implemented in MATLAB/Simulink and deployed to a real-time simulation by using an OPAL-RT simulator to validate the feasibility of the proposed model. The results for the real-time simulations are presented, showing the capabilities for voltage and frequency regulation of the controller, in load variations and fault condition.

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Publication Year:  2018
+ A 2 Kw, 2.85 Ghz Multipactor Rf Source Utilizing Depletion Mode Gan Hemts
  B. Esser; Z. Shaw; J. C. Dickens; A. A. Neuber
Abstract:  A pulsed RF source for multipactor research capable of providing 2 kW at 2.85 GHz to a multipactor test cell is described utilizing state-of-the-art GaN HEMTs from Cree/Wolfspeed and integrated GaN amplifier from Qorvo/Tri-Quint. A Mini-Circuits ZX95-2920CA+ VCO is used as the signal generator with low phase noise and modulation capable with a bandwidth of 55 MHz. An inline attenuator provides the operator power control in the range of approximately 42 to 64 dBm (16 to 2800 W). A high-speed RF switch creates a 100-microsecond pulse with a rise time of 25 ns and a typical switching time of 35 ns. A single Tri-Quint TGA2585-SM provides the majority of the gain in the system, 32 dB, and the necessary power for the final output stage (6 W). Four CGHV31500F amplifiers operating in parallel comprise the output stage providing the bulk of the power needed, 500 W each for a total of 2 kW with 12.5 dB gain each, with a single unit providing the necessary input power before splitting to the four finals (50.5 dBm, ~ 112 W). A custom PCB was designed to properly bias the GaN stages and prevent device failure due to improper bias sequencing. Custom power splitters and combiners had to be used due to the high-power levels being considered with directional couplers on the output to monitor output (forward) power and reflected (reverse) power during operation. This will provide valuable insight into characteristics of the plasma cloud generated during the multipactor event.

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+ A Renewable Solution Approach For Center Pivot Irrigation System
  V. Roy; S. S. Noureen; S. Bayne; A. Bilbao; M. Giesselmann
Abstract:  In this present study a hybrid renewable energy system is proposed to optimize the load demand for Center Pivot Irrigation System for remote cultivation areas in Lubbock, Texas. The energy resources included in the study are solar photovoltaic and wind energy. For the ease of study, a 120-acre cultivable land area is considered as model. Simulation and analysis of the load is developed using HOMER (Hybrid Optimization Model for Electric Renewable) software and the optimum use of renewable resources is determined. A RT-LAB based model is also developed to determine real time analysis of center Pivot load. As the impact of wind is remarkable and solar irradiance is significant in Lubbock area, the wind turbine and solar photovoltaic system is given priority for effective optimization. Using HOMER software and RT-LAB based analysis of different combinations and multiple components are considered for simulation study. An optimal solution is proposed in the work by considering the renewable energy resources as prime sources in Lubbock area for this optimization method.

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+ Analysis Of Commercial Gan Hemts In Overcurrent Operation
  M. Kim; J. A. Rodriguez; W. B. Ray; S. B. Bayne; H. O"™Brien; A. Ogunniyi
Abstract:  Gallium nitride (GaN) high electron mobility transistors (HEMTs) are an ideal option in applications of power electronics due to the wide-bandgap properties of the material. High electron mobility is gained through the device's unique channel structure. This research investigates whether state-of-the-art GaN HEMT semiconductors are reliable in a long-term operation in high power switch-mode conditions. Information on overcurrent capability about GaN HEMTs is not well established, thus a demand to investigate the devices exists. The GaN HEMT GS66508P from GaN Systems, was tested in pulsed overcurrent operations to establish the performance and to observe any operational changes after the experiment. The device is rated at 650 V and 30 A continuous. The goal of this research is to see if the device characteristics change after overcurrent pulsing and to analyze the device degradation that occurs in higher energy density.

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+ Analysis Of Dual Shock-Wave, Electric Pulsing Strategy For Electromanipulation Of Biomembrane Nanopores
  Q. Hu; A. R. Chowdhury; R. P. Joshi
Abstract:  Electric pulse driven membrane poration finds applications in the fields of biomedical engineering and drug/gene delivery. Shock waves are known to permeabilize cell membranes as well. Here we focus on the synergistic effects of both inputs in concert based on molecular dynamics simulations. Our results show that shockwaves could be used for pretreating cell membranes in the electroporation process. The dual strategy would either reduce the external voltage requirements (leading to more compact external circuitry) or help create larger pores. Furthermore, shockwaves could form pores at any desired membrane site location, and suitable combinations of nanojets and electric pulses would help control the aspect ratio and size as desired.

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+ Analysis Of Grid Connected Fuel Cell Power System Integrated With Supercapacitor
  N. Shamim; A. Bilbao; D. Reale; S. Bayne
Abstract:  This Paper analyses the integration of a super capacitor with fuel cell in grid connected mode. A super capacitor is a fast charging and discharging device. In a fault condition super capacitor will discharge and maintain the voltage of the DC bus. In this paper a mathematical model of the fuel cell power system is designed. A super capacitor and a grid are modeled in PSCAD simulation environment. The fuel cell power system is integrated with the grid using model predictive control technique. A fault is applied at the DC bus to study the impact of integrating a super capacitor with the fuel cell. The simulation results show the super capacitor can maintain the voltage at DC bus at fault condition.

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+ Assessing The Influence Of Secondary Electron Emission Characteristics On Multipactor In Rectangular Waveguides
  H. K. A. Nguyen; J. Mankowski; J. C. Dickens; A. A. Neuber; R. P. Joshi
Abstract:  Multipactor in a rectangular waveguide is studied using numerical simulations. Particular attention is given to the secondary electron emission characteristics including their energy spectrum (hence velocity spread) and angular distribution. Elastically scattered, rediffused and true secondary electrons are all comprehensively included based on the Furman-Pivi model [1] for the TE10 mode. The focus is on small waveguides and lowest order resonance conditions.

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+ Charge Plasma High Voltage Pin Diode Investigation
  M. J. Kumar; S. Hahmady; R. Gale; S. Bayne
Abstract:  In this paper, we investigate the new approach on designing a high voltage PIN diode without introducing any doping into the silicon. The concept of charge plasma is basically using different metals with appropriate work-function as anode and cathode contacts, which cause the formation of "p" and "n" plasma regions in silicon respectively. We have used the Silvaco Atlas simulation to compare the forward and reverse I-V characteristics of the proposed device with the conventional PIN diode. Also, we looked at the temperature dependency of their reverse saturation current. We demonstrate that by using the charge plasma concept, the proposed CP-PIN diode and conventional PIN diode have identical characteristics.

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+ Cst Particle-In-Cell Modeling Of A Tunable Reflex-Triode Vircator
  D. H. Barnett; A. A. Neuber; J. C. Dickens; J. J. Mankowski
Abstract:  This study serves to describe three-dimensional particle-in-cell (PIC) simulations of a tunable reflex-triode virtual cathode oscillator (vircator). Experimental data from the compact hard-tube reflex-triode vircator developed at Texas Tech University (TTU) is used to validate simulated results. The vircator developed at TTU is capable of burst-mode operation at pulse repetition rates (PRFs) up to 100 Hz for a period of one second. A pulse energy of 158 J drives the vircator, and 600 kV (open circuit) pulse forming network (PFN) based Marx generator. The vircator is comprised of a bimodal, carbon fiber cathode and a pyrolytic graphite anode, with the ability to quickly change the distance between the anode-cathode (A-K) gap, back wall distance, and bottom plate distance between experiments. The PIC simulations have been performed using CST PIC Solver, by Dassault Systemes. The models detail virtual cathode formation and the subsequent extraction of radiated microwave power for a variety of cavity geometries. A working three-dimensional, relativistic, electromagnetic, particle-in-cell model of a vircator allows for quick, predictive results relative to building an experimental setup. The model is used to determine the necessary driving voltages, A-K gap distances, and cathode current densities to extract microwave radiation at a desired. Simulated results aid in identifying mode contributions. Voltage, current, and microwave data are presented and compared against experimental results at different operating conditions.

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+ Design And Test Of A W-Band Photonic Bandgap Extended Interaction Klystron Amplifier
  J. C. Stephens; J. C. Tucek; M. A. Basten; K. E. Kreischer; M. A. Shapiro; R. J. Temkin
Abstract:  This report summarizes the progress of experimental efforts for the development a 94 GHz extended interaction klystron (EIK) with a photonic bandgap (PBG) based interaction structure. Input return loss measurements of the interaction structure are presented, demonstrating the successful fabrication of the input and output cavities of the EIK. Additionally, input return loss and insertion loss measurements of microwave-vacuum feedthrough windows are also presented. Finally, a review of the complete W-band experimental apparatus is given. Hot test experimental efforts for this study are expected to be completed by the 2018IVEC meeting.

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+ Electrically Small Antenna Design For Transportable Ionospheric Heating
  B. Esser; J. C. Dickens; J. J. Mankowski; A. A. Neuber
Abstract:  Ionospheric Heating, traditionally performed utilizing large fixed location arrays, while effective, limits research efforts to those fixed locations. As one may envision, a more compact transportable array will provide additional research opportunities at latitudes previously unexplored. For instance, closer to the equator where the Earth's magnetic field is primarily parallel to the ground. An electrically small inductively coupled antenna is considered for its suitability in such an array. A Small or Semi Loop Antenna (SLA) inductively couples to a Capacitively Loaded Loop (CLL) providing high efficiency and natural 50 $\Omega$ port matching. The CLL, of hinged petal design, consists of a large parallel plate capacitor, and half cylinder inductive sections which are hinged at the base to allow for tuning in the range of ionospheric heating (3 - 10 MHz) with a plate included angle of 0 - 16°. A prototype antenna was designed and evaluated at 1/10th scale - for ease of research efforts - with tuning range of 30 - 100 MHz including capability of tuning the coupling between SLA and CLL to achieve good source matching across the tuning range, particularly at the low and high ends. This tuning method may also be used to compensate for mutual impedance effects in array operation, improving array performance. A gain of approximately 5 dBi is observed when placed upon a sufficiently large ground plane. Tuning of the antenna prototype is achieved via stepper motor driven system to remotely adjust both the CLL and SLA angles continuously.

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+ Event Detection From Pmu Generated Big Data Using R Programming
  V. Roy; S. S. Noureen; S. B. Bayne; A. Bilbao; M. Giesselmann
Abstract:  Recent advancement in Power System Analysis shows that implementation of PMU (Phasor Measurement Unit) in Smart Grid playing a significant role over SCADA. The main reasoning for that is more sampling data than traditional SCADA system. Every PMU data like voltage, current and Phase angle gives more samples in every second which is helpful for event detection. The enormous data send by each PMU in every second energies the big data issue. To find out and predict the transient situation and even small disturbances or anomalies from big data analysis within the specified short period of time is a challenge for near future. Because introduction of new smart electrical devices will boost up the big data issue. Processing of big data for post disturbance analysis is also an important task. This paper gives a scenario of PMU measurements received to PDC (Phasor Data Concentrator) from PMUs placed in distinct locations and detection of transient events for post disturbance analysis. In this analysis, the disturbances are evaluated with the R programming analysis and compare findings of chronological data from separate locations and also shows the relation between disturbances in a grid. For this analysis, the impacts of frequency and voltage data are also considered.

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+ Fuel Cell Power System Integration With Grid Using Finite Set Model Predictive Control Technique
  N. Shamim; G. M. Munoz; D. Reale; M. Harral; S. Bayne
Abstract:  This Paper evaluates the integration of fuel cell power system with the grid using finite control set model predictive controller. A mathematical model of the phosphoric acid fuel cell power system is designed. The grid and the fuel cell are modeled in PSCAD simulation environment. Direct power control technique for model predictive controller is used to control the converter. The steady state results are shown in the paper, Also, a single phase fault and three phase fault is applied at the grid side to study the effect of integrating the fuel cell with the grid. The simulation results show model predictive controller can effectively integrate fuel cell with the grid.

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+ Fundamental Study Of Atmospheric Rf Breakdown At 3.3 Mhz
  I. A. Aponte; B. Esser; Z. Shaw; J. C. Dickens; J. J. Mankowski; A. A. Neuber
Abstract:  RF breakdown at a frequency of particular relevance to ionospheric heating - 3.3 MHz, close to the low end of the applicable frequency range - is studied at centimeter sized gap distances and compared to literature for small gaps. Paschen's famous DC breakdown study utilizing two brass spheres of radius 1 cm was recreated following the original procedure, from which the data was used to compare to a study of RF breakdown. Through testing it was found that brass as an electrode material exhibits a large standard deviation in breakdown voltage and as such stainless-steel Bruce profile uniform electric field electrodes were substituted. Steel's resistance to surface ablation provided for extremely low standard deviation of measurements and hence good repeatability. Additionally, unlike brass, steel is not contaminated through reaction with gaseous elements such as carbon, oxygen and nitrogen. Electrodes were polished to remove any field enhancements and cleaned of polishing compound such that dielectric inclusions were largely avoided.

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+ High Power Microwave Generation By Cherenkov-Cyclotron Instability In A Metamaterial Structure With Negative Group Velocity
  X. Lu; J. C. Stephens; I. Mastovsky; M. A. Shapiro; R. J. Temkin
Abstract:  We present the experimental results of a high power microwave source with a metamaterial structure designed at 2.4 GHz. The structure is a waveguide loaded with two metamaterial plates consisting of complementary split ring resonators placed in the waveguide with reverse symmetry. Two backward wave modes can propagate in the waveguide and interact with an electron beam of up to 490 kV, 84 A. Full microsecond long output microwave pulses up to 2.9 MW were measured with an efficiency of 9% from the Cherenkov-cyclotron instability.

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+ Investigation Of Gan Photoconductive Semiconductor Switches
  N. A. Wilson; J. A. Culpepper; V. Kuryatkov; M. Gaddy; J. C. Dickens; S. Nikishin; R. Ness; A. A. Neuber
Abstract:  The suitability of commercially available wide bandgap GaN material for the fabrication of photoconductive semiconductor switches, PCSS, was investigated. A variety of PCSSs were fabricated utilizing diverse GaN samples, which were shown to exhibit significantly diverse physical properties. That is, sample characterization techniques such as cathodoluminescence (CL), photoluminescence (PL), secondary ion mass spectrometry (SIMS), Current-Voltage behavior, and scanning electron microscopy (SEM) were applied to characterize the samples prior to processing.

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+ Micro-Grid System Modeling Efforts Using Pq-Control For Single-Phase And Three-Phase Inverter
  G. M. Quintero; Y. Reddy Challapuram; A. Bilbao; S. B. Bayne; A. S. Subburaj; M. A. Harral
Abstract:  The integration of Microgrids (MGs) into the mains must be done with consideration of control techniques that ensure the appropriate synchronization and power balance between distributed generators (DGs) and the grid. This paper presents the development of a PQ-control model for the grid connected single-phase and three-phase inverters present in the Distributed Asset Research Testing (DART) facility in Lubbock, Texas. In a grid-tied configuration, the inverters will operate as a current source that inject current into the grid based on the established reference setting of active and reactive power. To achieve this operation, the inverter current must be monitored, and it will be subjected to abc to dq0 transformation (Clarke and Park transformation). In the case of a single-phase inverter, two orthogonal phase variables are required in order to perform the Park transformation (αβ-dq). A phase shift of 90° with respect to the real phase variable is introduced to get the beta component required to complete this transformation. By showing the power characteristics in simulations, the proposed control strategy will be illustrated. The entire work is performed in MATLAB/SIMULINK environment.

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+ Modeling Of Inverters For Fuel Cells For Grid-Tied And Islanding Mode With Smooth Transitions
  Giesselmann, M; Bayne, S; Shamin, N; Kelley, M; Reale, D; Cingoz, F
Abstract:  We are reporting on models for a group of inverters that can feed real and reactive power into a utility grid in Grid-Tied mode and is able to smoothly transition to islanded mode. In grid tied mode, the inverters are operating in P/Q mode and inject controllable amounts of real and reactive power into the grid. In islanded mode the inverters are grid forming and share power using droop control. We are presenting MatLAB-Simulink models and results of the simulations including the transitions.
+ Modeling Power Factor Correction Circuits With Ltspice
  M. Giesselmann; V. Roy
Abstract:  LTspice is a powerful simulation language that is specifically optimized for modeling Switch Mode Power conversion. It is not limited to small numbers of nodes and freely available [1]. We are presenting several examples of simulations for popular electronic power factor correction circuits that improve the input power factor of AC Power Supplies by active wave-shaping of the AC input current and the associated avoidance of harmonics. The simulations are performed using a cycle-by cycle switching approach as well as using a time averaged PWM model. A fast inner current loop is controlling the shape of the input current such that it matches the sinusoidal shape of the AC input voltage. A time averaged PWM model is useful for fast simulations covering many cycles to design and study secondary feedback control that regulates the output voltage of the converter.

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+ Mouse Anatomical Cardinal Planes And Axes Towards Augmentation For Behavior Analysis
  S. B. Negrete; R. Prakash Joshi; R. Labuguen; J. Matsumoto; T. Shibata
Abstract:  In this paper, we propose a visualization framework for mouse anatomical cardinal planes and axes by extending an open-source platform called "3DTracker-FAB" and demonstrate its capability towards augmentation. Previously, the 3DTracker-FAB was only able to determine the mouse anatomical model, showing its head, neck, trunk, hip, and nose. We enhance the software to include body axes and planes of the subject in relation to its anatomical model. This work will help scientist working with animals since anatomical axis and planes are used for describing motion, and anatomical location.

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+ Numerical Studies Into The Possibility Of "Lock-On" In A Gan Photoconductive Switch For High Power Applications
  A. R. Chowdhury; R. P. Joshi
Abstract:  Time-dependent photocurrent response in semi-insulating GaN is simulated with a focus on the Lock-On phenomenon. A one-dimensional, time-dependent model based on the drift-diffusion theory is used. The model is tested for GaAs and shown to yield good agreement with data. The GaN simulations are then performed. The main findings are that deeper traps nearer the valence band at higher densities, and materials with larger high-field drift velocity would all aid in attaining Lock-On. The threshold field for Lock-on in GaN is predicted to be around 150 kV/cm, though this is strongly dependent on the trap parameters.

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+ Standardising Utility Savings
  M. Czerniak; A. Neuber
Abstract:  As the semiconductor industry makes devices and integrated circuits (ICs) that are increasingly complex, a consequence has been that the number of processing steps is increasing, from 400 at 90nm to > 1000 in state-of-the-art designs [1], shown in Figure 1. Furthermore, despite many process steps becoming more utility (and especially electrical power) - efficient, the increasing number of times a wafer visits process chambers has resulted in the energy use per cm2 wafer area increasing, reversing the trend of previous years. Figure 2 illustrates this phenomenon, which is also exacerbated by the use of double and quadrupole patterning, 3D device stacking and the use of EUV in HVM (which reduces the number of process steps but is utility-intensive).

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+ Surge Current Analysis Of Commercial Off-The-Shelf 1200 V Silicon Carbide Jbs Diodes And Mosfet Body Diodes
  J. Forbes; F. Salcedo; C. Tchoupe-Nono; R. Gale; S. Bayne
Abstract:  As an increasing number of silicon carbide (SiC) power semiconductor devices become commercially available, and as silicon devices have reached their theoretical power density limits, SiC devices are being utilized in an increasing number of power electronics and pulsed power applications. A few examples of these applications include high-power DC-DC converters, inverters, motor drives, or high-voltage pulse generators such as a solid-state Marx generator. To encourage further adoption of SiC devices in these and other applications, further reliability testing and analysis must be conducted. One parameter that is important to study is the surge current capability of both SiC diodes and the body diodes of SiC MOSFETs. In this research, a surge current testbed was designed and built to test commercially available 1200 V / 10 A SiC JBS diodes from 3 different manufacturers, and the body diodes of 1200 V / 10 A SiC MOSFETs from 3 different manufacturers. The purpose of this work is to independently verify manufacturer datasheet claims regarding the surge current capabilities of their diodes. In addition, surge current ratings on the body diodes of the SiC MOSFETs are determined and published.

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Publication Year:  2017
+ 160 J, 100 Hz Repetition Rate, Compact Marx Generator And High Power Microwave System
  Barnett, DH; Rainwater, K; Dickens, JC; Neuber, AA; Mankowski, JJ
Abstract:  This paper presents the electrical and mechanical hardware considerations of a compact, 160 J modular pulse forming network (PFN) Marx generator used to drive a high-power microwave (HPM) source that is a time variant load at a PRF of 100 Hz. The modular Marx generator is designed to produce an open-circuit output voltage of 600 kV from a 50 kV source using twelve stages. Each stage of the Marx was constructed from a PFN fashioned from five, 2.1 nF, high voltage capacitors in parallel. Each Marx module was machined out of acetyl copolymer or Delrin (c) to provide optimal strength, rigidity, and a dielectric constant that closely matches transformer oil. These Marx modules include air supply lines that are machined directly into each block of Delrin (c) allowing airlines to connect to each module chamber rather than every spark gap. Each module has two electrode inserts placed into the sealed pressure vessel contained within the module. After the Marx erects, the energy is directed into the virtual cathode oscillator (vircator) where subsequent frequency generation is manipulated through a rectangular waveguide contained within a new resonator cavity design. The new design allows the bottom wall, back wall, and anode cathode gap to be moved by two linear actuators, a linear bellows, and another linear actuator, respectively. The cavity is contained within a 10-inch circular vacuum chamber with a round stainless steel sleeve running from the back wall to the linear bellows. Contained within the round sleeve is a rectangular waveguide where the bottom wall and the cathode are housed. The anode is connected to the Marx generator via a nickel shaft that feeds through the back wall into the circular sleeve and into the rectangular waveguide. The anode made from pyrolytic graphite, remains stationary while the bottom wall, and carbon fiber velvet cathode move relative to its position. The benefit of this design is the height and depth of the cavity resonator can be controlled independently of each other while still allowing the A-K gap to be manipulated on its own.
+ A Study On Human-Robot Collaboration For Table-Setting Task
  K. Saxena; R. Labuguen; R. P. Joshi; N. Koganti; T. Shibata
Abstract:  As the robot technology is advancing, it is possible to use robots for basic day-to-day chores, so that the burden can be taken off from humans. To make the robots perform such tasks, it is necessary for them to handle different types of objects. Manipulation of deformable objects such as cloth is a challenging task for a robot because of high dimensionality and large number of possible configurations of cloth. Previous studies have covered large number of simple manipulations of cloth articles. In this paper, we are focusing on table setting task that requires putting on a sheet of cloth on the table. This paper proposes human-robot collaboration for table-setting task based on visual assessment. We used Baxter robot to hold two corners of rectangular tablecloth and other two corners are held by human. A head-mounted Kinect sensor is used to get the state of cloth and Robot arms are used for controlling the position of cloth corners. We use features from Kinect sensor to assess whether the placement of the cloth is successful or not. We demonstrate an initial study of the system that can achieve promising results towards table setting task through human-robot interaction.

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+ An Overall Study Of A Real-Time Simulator And Application Of Rt-Lab Using Matlab Simpowersystems
  S. S. Noureen; V. Roy; S. B. Bayne
Abstract:  This paper summarizes the features and advantages of the renowned Real-Time Digital Simulator (RTDS) called OPAL-RT Simulator. Alongside with its applications in the electric power system for the system design, analysis and testing. This comprehensive study also includes a brief description of its software, hardware, I/O system, modeling, Hardware-in-the-Loop and other prospects. Tremendous advancement in the storage capacity and computational speed of the modern computer system has done for the last few decades. Assimilating this advancement, this simulation tool has designed with unique features like real-time model-in-the-loop, Hardware-in-the-loop. Also for moderate operational and maintenance cost, OPAL-RT Simulator has become more prevalent to the researcher. There are immense scopes of experimental research in power systems analysis. This is the prime reasoning for describing the necessity and significance of OPAL-RT simulator in this work. In addition, a semi-simulation experiment of a PV system is presented using RT-LAB software. Two of the most salient tools of OPAL-RT are 1) RT-LAB and 2) ARTEMIS, which were applied in power electronics are also summarized.

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+ Current Handling Capability And Bond Degradation Of Bond Wires Under Pulsed Conditions
  R. Rodriguez-Molina; D. Mauch; V. Meyers; A. Neuber; J. Dickens
Abstract:  Results detailing the current handling capability of Gold bond wires (1 mil diameter), and Aluminum ribbon (1mil x 10 mil) under pulsed conditions are presented. Gold wire bonds were formed through the ball-bonding technique, and the Aluminum wire was bonded through the wedge bonding technique. Both wires were bonded to gold plated bond pads. Varying peak current densities ranging from $2 \mathrm {x}10 ^{4}\mathrm {A}$ cm $^{-2}$ to $2 \mathrm {x}10 ^{7}\mathrm {A}$ cm $^{-2}$ were applied to bond wires at pulse-widths ranging from 50 ns to $500 \mu \mathrm {s}$. In addition, the effect of surrounding medium (SF6, HV epoxy, transformer oil) on the current capability was investigated. Failure modes observed were investigated with SEM imaging, and the evolution of these failure modes during current pulsing was captured with high-speeding imaging. Finally, the obtained results are compared with the experimental and theoretical results obtained from previous investigations conducted on exploding wires.

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+ Design Of A 94 Ghz Photonic Bandgap Based Extended Interaction Klystron Amplifier
  J. C. Stephens; G. Rosenzweig; M. A. Shapiro; R. J. Temkin; J. C. Tucek; M. A. Basten; K. E. Kreischer
Abstract:  A complete design of a 94 GHz extended interaction klystron (EIK) amplifier has been developed at the MIT Plasma Science and Fusion Center. The device utilizes a novel, mode selective photonic bandgap (PBG) structure which enables the use of a modified PBG coupling scheme. Using particle-in-cell simulation, the EIK is predicted to generate 42 dB of gain and 130 W saturated power.

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+ Design Of Oversized Twts With Photonic Band-Gap Structures
  G. Rosenzweig; J. C. Stephens; M. A. Shapiro; R. J. Temkin
Abstract:  The challenge in manufacturing Traveling Wave Tubes (TWTs) at high frequencies is that the sizes of the structures scale with, and are much smaller than, the wavelength. This requires advanced nano-machining techniques or sheet-beam devices and puts strict limits on the peak output power that can be safely handled by the devices. Furthermore, the diameter of the electron-beam tunnel limits the amount of beam current, requires high magnetic fields for beam compression and creates difficulties in alignment.

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+ Developing A High Power, Pulsed Uv Led System For Photoconductive Switching Applications
  N. A. Wilson; D. L. Mauch; V. E. Meyers; J. C. Dickens; A. A. Neuber
Abstract:  Summary form only given. A very compact system integrating a high voltage pulser (up to 250 V) and high power UV LED (365 nm wavelength) was developed for triggering SiC photoconductive semiconductor switches (PCSS). The relationships between LED drive current and forward voltage to optical power were established for currents ranging from 0 A to 100 A at pulse widths ranging from 100 ns to 5 μs. The maximum optical power observed was 25 W. An optical system composed of a parabolic reflector and short focal length lenses was used to focus the emitted light onto a lateral geometry PCSS. The observed delivery efficiency was 63% onto a target 11 mm in diameter. Using the developed system, a SiC PCSS could be successfully triggered under high impedance load conditions.

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+ Electric Field Breakdown Versus Frequency Simulated Under Atmospheric Conditions For Large Gaps
  H. K. Nguyen; A. Chowdhury; J. C. Dickens; R. P. Joshi; A. A. Neuber
Abstract:  Breakdown of air at atmospheric pressure in response to AC fields in gaps larger than 1 cm was simulated. Most previous literature concerning breakdown in this regime has focused on much smaller gaps1.

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+ Epp-Dmm: An Efficient And Privacy-Protected Delegation Scheme For Matrix Multiplication
  Zhang, SM; Li, HW; Dai, YS; He, M; Lu, RX
Abstract:  In cloud computing, outsourcing computation, as an economically promising paradigm, enables clients with limited computing resources to delegate intensive tasks to the powerful cloud server. Nevertheless, outsourcing the involved data without encryption to public brings a high risk of revealing the confidential information of the client, and no matter the returned results from server are valid or not. Due to the low trustiness of the server, it is crucial to guarantee both the security and efficiency in delegation. Motivated by those challenges, a rapidly-growing body of research mostly focuses on how to delegate mostly utilizing a feasible mechanism-verifiable computation, where the server returns results along with corresponding verification proofs. In this paper, we propose an efficient and privacy-protected delegation scheme for matrix multiplication (EPP-DMM) of amortized model. EPP-DMM can realize efficient public verification together with sensitive protected data. Security analysis proves the reliability and security of our scheme, while performance evaluation presents the efficiency compared with other schemes.
+ Evaluation Of High Frequency Solid State Switches For Pulsed Power Applications Using A 12 Kw Variable Voltage Testbed
  Flack, T; Parson, J; Bittner, K; Driver, B; Zameroski, N; Bayne, S; Hettler, C
Abstract:  Field Effect Transistor (FET) controlled devices, such as MOSFETs and IGBTs, exhibit several desirable characteristics over other solid-state devices for pulsed power applications; benefits include high frequency switching, voltage control, and compact control circuitry. This paper details a testbed used for evaluation of the switching performance and characterization of FET controlled devices used in pulsed power systems as well as the diagnostics used to characterize the devices under test (DuT). The testbed presented in this research operates in two modes: (1) High energy pulsed mode, with charge voltages up to 300 V, pulse width of 3 seconds and up to 18 kJ total stored energy (2) Continuous pulse-train mode, with charge voltage up to 300 V, up to 18 kJ total stored energy and average current output up to 40 A. Both of these modes utilize a 396 mF capacitor bank to store energy. A fast, custom, gigabyte-memory-depth data acquisition oscilloscope records voltage and current waveforms at a 60 Mega-Sample/second rate. Due to the frequency regime (1-50 kHz), high current levels (up to 300 A peak) and wide voltage range of these experiments, making these measurements, reliably, is a non-trivial effort. Several methods of making each measurement were examined. Calibrated voltage, current, energy, and power waveforms quantify the DuT's turn-on / conduction / turn-off characteristics. Measurements of interest in these experiments are device current and device voltage; energy dissipated in the DuT is determined from these measurements.
+ Magnetic Field Diffusion Into Hollow Conductors With Walls On The Order Of The Skin Depth
  Buntin, T; Collier, L; Dickens, J; Mankowski, J; Walter, J; Neuber, A
Abstract:  Transient magnetic diffusion through conductors of thickness comparable to the skin depth is investigated. Since an analytical solution is unavailable in this case, such magnetic diffusion results must be determined via simulation or experimentation. In the experimental approach, a sinusoidal current with peak values in the range of 20-30 kA (approx. 7 kHz ringing frequency) is passed through a two turn coil generating a sinusoidally varying magnetic field. A hollow structure with metallic walls of controlled thickness is placed roughly 10 cm away from the exciting coil. The focus of this investigation is on the transient skin depth, which occurs during the first half-wave of the signal, as that is most relevant for pulsed power applications. A calibrated B-dot probe placed inside the structure facilitates measurement of the diffused field. As expected, experimental data shows that magnetic field diffusion through the wall is not instantaneous, causing a delay before the diffused field is measured inside the test structure. The impact of cracks and holes in the conductor on the speed and magnitude of the magnetic field diffusion is elucidated. Results for materials of different conductivities are compared and analyzed for the transition between thin and medium walled cases. FEM simulations are validated alongside these experimental results and used to access a larger parameter space.
+ Model Predictive Control Analysis For The Battery Energy Storage System
  N. Shamim; A. Subburaj; S. Bayne
Abstract:  This paper describes the Model Predictive Control technique for three phase bi-directional converter to integrate a battery system with the grid. The paper presents an overview of different predictive control technologies. The paper describes the basic concept, operating principle, governing equations and control algorithm of model predictive control for the power converter. The control technique is analyzed to integrate a 1MWh battery system model with the grid. The analysis is done in PSCAD simulation environment for both steady state and fault scenarios. The simulation results are presented to show the effectiveness of Model Predictive Control technology for battery integration.

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+ Narrow Pulse Evaluation Of 15 Kv Sic Mosfets And Igbts
  Hirsch, EA; Schrock, JA; Bayne, SB; O'Brien, H; Ogunniyi, A
Abstract:  With the progression of silicon carbide (SiC) technologies, single semiconductor switches with higher voltage and current capabilities are emerging. Evaluating the pulsed current capability of SiC semiconductor devices for pulsed power and power electronics applications is required to understand their performance and reliability. This paper presents the narrow pulse evaluation of 15 kV SiC MOSFETs (0.25 cm(2) active area) and IGBTs (0.32 cm(2) active area) with pulse widths in the range of 500 ns to 2 mu s. Testing results are presented with an 8 kV charge voltage and 50 A and 330 A peak conduction current for the MOSFET and IGBT, respectively. A fairly low inductance (< 500 nH) RLC circuit was used to generate the pulses and the device under test (DUT) was switched off during the pulse to create a trapezoidal type current waveform through the device. Transient characteristics, such as turn-on and turnoff times and energies, were measured to benchmark the devices(narrow pulse characteristics. The results presented in this paper demonstrate the characteristics of these devices for over-current narrow pulse applications.
+ Next Generation Ionospheric Heater Array
  B. Esser; J. C. Dickens; J. J. Mankowski; A. A. Neuber
Abstract:  An electrically small antenna (ESA) is evaluated for its potential future use in a Transportable Ionospheric Heating (TIH) array. Consisting of a Small Loop Antenna (SLA) which inductively couples to a Capacitively Loaded Loop (CLL) the antenna provides a high-Q natural match to a $50 \Omega $ source. The capacitance of the CLL may be adjusted to tune the antenna in the range of ionospheric heating of approximately 3 "“ 10 MHz. Several methods are evaluated to achieve this tuning including a horizontal sliding plate design, and a hinged petal design.

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+ Optical Nonlinear Absorption Properties Of 4H-Sic-Experiment And Model
  Meyers, V; Mauch, D; Dickens, J; Neuber, A
Abstract:  Intensity-dependent nonlinear light absorption in bulk 4H-SiC at the above-bandgap energy of 3.49 eV (lambda = 355 nm) is studied. Characterization and understanding of such nonlinear optical behavior in 4H-SiC forms the basis efficiency improvements and design of optoelectronic SiC devices, including photoconductive semiconductor switches. It is noted that previous research performed elsewhere had focused primarily on nonlinearities at below-bandgap energies, while little had been explored above-bandgap. In this study, absorption of short laser pulses with fluences ranging from 1 mJ/cm(2) to 30 mJ/cm(2) incident on 160 mu m-thick high purity semi-insulating 4H-SiC samples of varying recombination lifetimes is addressed. Sample bulk recombination lifetimes vary from 0.5 ns to 100 ns displaying the range of effects from growth, electron irradiation, and annealing. The effective absorption coefficient varies significantly within this range as an apparent function of bulk recombination lifetime. A four-level time-and space-dependent finite difference time domain (FDTD) model taking into account electron trapping, interband absorption, and free-carrier absorption was constructed that yielded further insight into the absorption dynamics. For instance, the importance of free carrier absorption and deep-level trapping in the nonlinear absorption behavior is elucidated.
+ Phasor Measurement Unit Integration: A Review On Optimal Pmu Placement Methods In Power System
  S. S. Noureen; V. Roy; S. B. Bayne
Abstract:  The Phasor Measurement Unit (PMU) is an imperative part for monitoring, protecting and controlling the current power system. For the current power systems, PMUs not only offer the synchronized measurements of real-time data of voltage but also the current and frequency. Placement of PMUs in each bus for monitoring the system is not feasible from economic point of view and also for big data handling. So it is an obligatory matter to reduce the number of PMUs in the bus system with the aim of attaining the maximum power system observation. Different techniques are being applied from past to present to solve this optimum PMU placement (OPP) problem such as heuristic method, mathematical programing. Heuristic method is a quick experience-based technique for solving the optimization problems. Various optimization methods for solving the OPP problems are being reviewed in this paper.

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+ Reconfigurable High Voltage Load For Pulsed Power Applications
  Kim, M; Forbes, JJ; Bilbao, AV; Schrock, JA; Bayne, SB
Abstract:  The evaluation of pulsed power systems and their constituent components requires unconventional loads with exceptional voltage, current, impulse energy, and continuous power dissipation capability. This paper presents the design and construction of a reconfigurable resistive load with active temperature monitoring for the evaluation of ultra-high voltage pulsed power modulators and semiconductor devices. The load consists of a network of 15 ceramic resistors (outer diameter of 2.54 cm and length of 30.48 cm) mounted vertically in an oil filled aluminum tank. To enable exceptionally high-power dissipation, the oil is pumped through the tank and through a radiator. A microcontroller based module activates a fan on the radiator if a preset oil temperature is surpassed. Experimental results gathered demonstrate that the load withstood 10 kW at 10 kV for 30 minutes, and that the temperature of the oil reached 80 degrees C.
+ Results Of A Compact Reflex Triode With Multi Cavity Adjustment
  Barnett, DH; Rainwater, K; Dickens, JC; Neuber, AA; Mankowski, JJ
Abstract:  This study focuses on achieving wide tunability of a compact reflex triode virtual cathode oscillator (vircator). The cathode is of a bimodal carbon fiber (CF) material paired with a pyrolytic graphite anode. These materials display ideal operating characteristics which include but are not limited to, long lifetime > 10(6) shots, high operating temperatures > 1000 K, and large current densities similar to 200 A/cm(2). A 12 stage, 158 J pulse forming network (PFN) based Marx generator serves to drive the vircator at 350 kV, 4 kA with similar to 100 ns pulsewidth. The operating frequency of interest is in the range of 1-6 GHz, where tunability is achieved by varying the length of the anode-cathode (A-K) gap, the length from the back wall to the A-K gap, and/or the distance from the bottom of the cavity to the A-K gap. The primary focus in this research was to increase the achievable frequencies by placing a square waveguide within a sealed vacuum tube. This allows the bottom part of the waveguide to be easily adjusted while still maintaining the waveguide integrity. The resulting microwave frequencies are shown along with the system performance.
+ Robotic Cloth Manipulation For Clothing Assistance Task Using Dynamic Movement Primitives
  Joshi, RP; Koganti, N; Shibata, T
Abstract:  The need of robotic clothing assistance in the field of assistive robotics is growing, as it is one of the most basic and essential assistance activities in daily life of elderly and disabled people. In this study, we are investigating the applicability of using Dynamic Movement Primitives (DMP) as a task parameterization model for performing clothing assistance task. Robotic cloth manipulation task deals with putting a clothing article on both the arms. Robot trajectory varies significantly for various postures and also there can be various failure scenarios while doing cooperative manipulation with nonrigid and highly deformable clothing article. We have performed experiments on soft mannequin instead of human. Result shows that DMPs are able to generalize movement trajectory for modified posture.
+ Silvaco-Based Electrothermal Simulation Of 10 Kv 4H-Sic P-I-N Diode Under Pulsed Condition
  Pushpakaran, B; Bayne, S; Ogunniyi, A
Abstract:  The application of silicon carbide technology in p-i-n diode has facilitated the development of p-i-n rectifiers up to several kV blocking voltage with a much thinner drift region thickness as compared to its silicon counterpart. This research focuses on the 2D electrothermal simulation of a 10 kV 4H-SiC p-i-n diode model developed using Silvaco ATLAS software. The p-i-n diode structure was designed for 100 A/cm(2) forward current density with a cell pitch of 16 lam and an active area of 10 mu m(2). Physics based models were included to account for low-field mobility, carrier-carrier scattering, carrier generation recombination, avalanche breakdown, and lattice heating. The device model was simulated under steady state and transient conditions. Pulsed simulation of the p-i-n diode was carried out using an RLC ring down circuit to generate a 5 mu s wide pulse with peak current densities up to 5000 A/cm(2). The reverse recovery characteristics of the diode was analyzed for a forward current density of 100 A/cm(2) and varying turn-OFF dJ/dt to assess the limitation on usable switching frequency. Lattice temperature profile of the p-i-n diode was generated by including heat generation models during transient simulation to identify thermal hot spot formation and areas of possible failure during pulsed operation.
+ Silvaco-Based Evaluation Of 10 Kv 4H-Sic Mosfet As A Solid-State Switch In Narrow-Pulse Application
  Pushpakaran, B; Bayne, S; Ogunniyi, A
Abstract:  Key requirements for a solid state switch in a fast switching pulsed power circuit include high blocking voltage, high current conduction and fast switching capability. Typical pulsed power applications like plasma initiation and high-energy LASER require operating voltages in the order of several kilovolts. The development of a multi-kilovolt SiC MOSFET for fast switching pulsed power application would require detailed analysis of the device switching characteristics. Since the switching speed of a MOSFET is primarily dependent on the inter-electrode capacitances, it becomes critical to have a comprehensive understanding of the device capacitance and its effect on the gate driver requirements for narrow-pulse switching. In this research, 2D model of a 10 kV 4H-SiC MOSFET was developed using Silvaco ATLAS TCAD software and simulated for its steady state, AC, and transient characteristics. The device cell was designed for an active area of 5 mu m(2) and 100 A/cm(2) drain current density. The capacitance-voltage and gate charge curve for the SiC MOSFET were obtained via AC and transient simulation respectively. This data was used to estimate the gate drive requirements for the device under fast switching conditions.
+ Stability Analysis Of A.C. And D.C. Microgrids Using Opal-Real Time Digital Simulator
  A. Subburaj; A. R. Arra; S. Bayne
Abstract:  In recent years the significant improvementin micro grid technology has led to the utilization of thelocal distributed sources. The microgrids also have agreater role in the minimization of transmission losses. During power blackouts they serve as a main source ofpower for few emergency loads. It is common that usuallythe AC grids are preferred over DC grids to transmitpower over long distances in spite of various issuesassociated with AC grids such as frequency dip, voltagedrop due to reactance, charging currents, leakagecurrents, low power factor problems, skin effect andFerranti effect. One of the major reasons for suchpreference is that voltage can be easily stepped up orstepped down using transformers. Whereas in a DC gridsystem voltage conversion accounts for switching lossesand equipment costs. But at the micro grid level the supplyvoltages are low, and most of them are DC sources. Theenormous growth in the power semiconductor technologymakes it possible to convert voltages in DC with low costand reduced power losses. The AC and DC microgridmodels were developed in MATLAB/SIMULINKenvironment. The stability and transient analysis areperformed during faults and sudden load variations onboth the AC and DC microgrids in real time using OPALRTreal time digital simulator. The effects of stability on aweak grid scenario have been analyzed for both AC andDC microgrids.

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+ Toward The Development Of An Efficient Bulk Semi-Insulating Gan Photoconductive Switch
  V. Meyers; D. Mauch; V. Kuryatkov; S. Nikishin; J. Dickens; A. Neuber; R. Ness
Abstract:  Photoconductive semiconductor switches (PCSS) made from bulk, semi-insulating GaN have been fabricated and tested under pulse-charged conditions. Switching response and photocurrent efficiency of GaN PCSSs triggered by sub-10 ns, 355 nm laser pulses is reported. It is shown that fast rise time (<;300 ns) voltage pulses can be used to charge a GaN PCSS to fields well beyond the DC breakdown field strength of GaN and improve switching performance. GaN's wide band gap, breakdown field strength, and electron mobility make it a material superior to SiC and far superior to GaAs for PCSS applications, though historically these materials have dominated PCSS research due to their relative ease of fabrication. Recent improvements to crystal quality and wafer size have allowed GaN and more recently semi-insulating GaN to play an increasing role in high-power and high-voltage solid state devices.

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+ Wide Injection Range Ocvd System For Lifetime Spectroscopy Techniques
  S. Lacouture; J. Schrock; E. Hirsch; S. Bayne; H. O'Brien; A. A. Ogunniyi
Abstract:  To continually increase the voltage and current capabilities of power semiconductor devices, whether pushing older materials such as Si to its' intrinsic electrical limits or by employing newer substances like SiC or GaN, a thorough understanding of the entire device is required, from the basic physics of the material and its interactions with defects and passivation, up to the complete device structure, including terminal performance and device - level limitations. Of the fundamental parameters that affect device performance, the most complex and malleable is the carrier lifetime. Carrier lifetime has a profound effect on power devices designed for high voltage applications and power devices relying on conductivity modulation. This parameter cannot be given as a ball - park figure unlike mobility (and hence diffusion coefficients) as it is affected by nearly every processing step a device undergoes: a final device can have carrier lifetimes that differ drastically from the starting bulk material. The work herein utilizes a relatively new set of techniques collectively known as Lifetime Spectroscopy (LS) methods to extract fundamental material parameters relating to recombination activity: τη0, τρ0 and AEt. These LS methods directly measure recombination activity of defects and hence acquire characteristic data of defects and dopants that is complimentary in nature to the information gleaned about them from more orthodox methods such as Deep - Level Transient Spectroscopy (DLTS). The Open Circuit Voltage Decay (OCVD) method is used along with improved data manipulation algorithms to extract the effective carrier lifetime as injection and temperature are swept. A complete stand - alone system has been constructed that allows a very wide range of current injection (~1mA to > 200A) and built - in OCVD waveform acquisition. The first complete Temperature - Injection Dependent Lifetime Spectroscopy (T-IDLS) studies are carried out on a small signal PiN commercial diode.

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Publication Year:  2016
+ A 160 J, 100 Hz Rep Rate, Compact Marx Generator For Driving And Hpm Source
  Rainwater, K; Barnett, D; Lynn, C; Dickens, J; Neuber, A; Mankowski, J
Abstract:  This paper presents the electrical and mechanical design considerations of a compact, 160 J modular pulse forming network (PFN) based Marx generator used to drive a high-power microwave (HPM) source with a time variant load at a PRF of 100 Hz. The modular Marx generator is designed to produce an open circuit output voltage of 600 kV from a 50 kV source using twelve stages. Each stage of the Marx was constructed from a PFN created with five, 2.1 nF, high voltage capacitors in parallel. Each Marx module was machined out of acetyl copolymer or Delrin to provide optimal strength, rigidity, and a dielectric constant that closely matches transformer oil. These Marx modules include air supply lines that are machined directly into each block of Delrin allowing airlines to connect to each module chamber rather than every spark gap. The spark gaps are comprised of two electrode inserts placed into the sealed pressure vessel contained within the Marx modules. The electrode inserts are of a sleeve-electrode design, which allows the user to insert the electrode into the sleeve, then the sleeve into the Marx module. The benefit of this design is the ability to adjust the electrode gap spacing without compromising the high pressure seal. Two continuous charging inductors run between each PFN and underneath the Marx modules. Due to high voltages generated by the Marx, outer field shaping rings are used to reduce the field stress across the induction coils, resulting in longer lifetime. The inductors are also of modular design allowing for individual coils to be replaced in the event of failure. Output voltage and current waveforms from a 60 Ohm water load are presented.
+ Analysis On Repetitive Pulsed Overcurrent Operation Of Gan Power Transistors
  W. B. Ray; M. Kim; A. Bilbao; J. A. Schrock; S. B. Bayne
Abstract:  Gallium Nitride (GaN) transistors are of great interest for pulsed power and high power applications due to the proven capability of Silicon Carbide (SiC) transistors. Due to recent advances in GaN power semiconductors, lateral GaN transistors need to be evaluated for their performance under repetitive pulsed overcurrent operation that can occur in power electronics or pulsed power applications. A normally-off GaN Systems GS61008P-E03-TY was evaluated in a pulsed ring down circuit at peak currents of up to 230 A over frequencies ranging from 0.5 to 20 Hz. Measurement of switching transient energy dissipation showed minimal difference over cumulative pulse history and pulse frequency. In addition, the device's electrical characteristics, including forward IV and transconductance, were measured throughout testing and revealed no significant degradation. These results demonstrate the GaN FET's robust ability to handle transient pulsed overcurrent conditions common for commercial power semiconductor device applications.

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+ Battery Connected Dfig Wind System Analysis For Strong/Weak Grid Scenarios
  A. S. Subburaja; N. Shamim; S. B. Bayne
Abstract:  The paper helps to understand the performance of the grid with battery and doubly-fed induction generator (DFIG) wind turbines when operating in a weak grid scenario with a low short circuit ratio (SCR). The concept will analyze the performance of the grid with battery connected DFIG both in steady state and transient scenario. The grid can be represented as a Thevenin equivalent circuit and is rated at 12.5 kV. A battery system and a wind system are connected at the point of common coupling (PCC). The battery system being modeled in PSCAD software is rated at 1 MW/1 MWh and the wind system model is rated at 2 MW. The grid has been characterized and analyzed based on two categories: strong grid and weak grid. A grid is considered to be weak when the flow of active and reactive power in the network causes a significant amount of voltage fluctuation at the point of common coupling. A grid is considered to be strong when the grid is stable with allowable nominal deviations with voltage and frequency. The strength of the grid can be measured by taking the ratio of grid's short circuit power with grid nominal power.

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+ Breakdown Characteristics Of A Silicon Carbide Photoconductive Semiconductor Switch Triggered Spark Gap
  T. Ihara; D. Mauch; J. Dickens; A. Neuber
Abstract:  Summary form only given. Development of a switch capable of operation at high voltages, high repetition frequency, with long lifetime is essential for furthering pulsed power applications. Photoconductive semiconductor switches (PCSSs) possess inherent optical isolation and extremely low switching jitter (~10 ps), and have also been experimentally shown to be capable of switching high voltages (up to 50 kV) and currents with very fast rise and fall times (<; 1 ns)[1-2]. In this paper, we report the breakdown characteristics of a SiC PCSS triggered spark gap obtained via measurement of the voltage and current, and simulation of the electric field distribution. The triggered spark gap is composed of sphere-to-sphere electrodes and a field distortion electrode, which is kept at mid-potential in the center plane between the two spherical main electrodes. A normally open PCSS is connected between one of the main electrodes and the mid-plane (trigger) electrode, whose center bore diameter is varied from 5 to 15 mm. With application of the optical pulse to the PCSS, the trigger electrode is temporarily connected to the main electrode, effectively doubling the electric field between the trigger and opposite electrode, leading to main gap closure. In essence, while bulk SiC PCSS switching currents demand very high optical power input, the synergy of bulk SiC PCSS and traditional spark gaps enables the triggering of large current flows at very modest optical powers with low jitter. Overall, the obtained results reveal that incident laser energy and mid-plane electrode geometry heavily influence the breakdown characteristics of the spark gap including jitter time, and breakdown voltage.

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+ Charge Transfer-Based Sensorless Voltage Feedback In Hv Capacitor Chargers
  A. V. Bilbao; M. G. Giesselmann; S. B. Bayne
Abstract:  Rapid capacitor chargers are typically used to charge a bank of capacitors with the purpose of discharging it into a pulsed power load [1,3]. Previous research shows that the charging voltage of the load can be accurately calculated in real-time using microcontroller software algorithms [1,5]. The objective of this paper is to report a hardware based approach to measure the charge transfer into the load capacitor and implicitly the capacitor charging voltage. The proposed circuit uses operational amplifiers in order to integrate the input charge. A microcontroller receives the integrated signal to compute the output voltage and stop the charging process when the target voltage has been reached. Failure to accurately detect the end of charge time could lead to an excessively large capacitor bank voltage. For this reason, the proposed method can be utilized as a primary means of end-of-charge detection in conjunction with a traditional voltage sensing scheme.

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+ Continuous Switching Of Ultra-High Voltage Silicon Carbide Mosfets
  A. V. Bilbao; J. A. Schrock; M. D. Kelley; E. Hirsch; W. B. Ray; S. B. Bayne; M. G. Giesselmann
Abstract:  Silicon carbide power semiconductor devices are capable of increasing the power density of power electronics systems [1, 2]. In recent years, devices rated to block voltages up to 20 kV have been demonstrated [3]. These research grade devices must be fully characterized to determine operating characteristics as well as failure mechanisms. The purpose of this paper is to demonstrate the continuous switching performance of ultra-high voltage metal oxide semiconductor field effect transistors (MOSFET) rated for 15 kV / 10 A. A high voltage boost converter was developed to evaluate the continuous switching performance where the high-voltage MOSFET is utilized as the main switching element. During operation, the on-state voltage, gate leakage current, and dc characteristics are monitored to determine device degradation. Measured device degradation is presented as a comparison of initial and final dc characterization.

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+ Evaluation Of Long Term Reliability And Safe Operating Area Of 15 Kv Sic Pin Diodes During Ultra-High Current Pulsed Conditions
  Hirsch, EA; Schrock, JA; Lacouture, S; Bilbao, A; Bayne, S; Giesselmann, M; O'Brien, H; Ogunniyi, A
Abstract:  Silicon Carbide (SiC) is a leading wide bandgap semiconductor for increasing the power density of high power applications. This paper overviews the long term reliability and safe operating area of 15 kV SiC PiN diodes during pulsed current conditions. An automated system is used to stress these devices with ultra-high current pulses and monitor degradation with in-system characterization. The system is capable of a 100 mu s full-width half maximum pulse width up to 15 kA, with a repetition rate of 0.5 Hz. Periodic in-system characterization measures device forward conduction and reverse breakdown. The devices in this paper are pulsed at current levels from 1.5 kA to 2.5 kA. Over 100,000 pulses at 1.5 kA have been performed with no degradation. The long term reliability and failure mode results for the 15 kV PiN diodes will be reviewed.
+ Frequency Tunability Of A Reflex-Triode Vircator Using Particle-In-Cell Modeling
  P. M. Kelly; C. F. Lynn; J. M. Parson; J. Dickens; A. Neuber; J. J. Mankowski
Abstract:  Summary form only given. The results from the development of a three-dimensional particle-in-cell (PIC) model investigating frequency tunability of a reflex-triode virtual cathode oscillator (vircator) are presented. These efforts have focused upon achieving stable frequency output at many different frequencies in the S, L, and C-bands, from a single tube, using the ICEPIC (Improved Concurrent Electromagnetic Particle-In-Cell) code from the Air Force Research Laboratory (AFRL). Experimental data from the hard-tube vircator at Texas Tech University (TTU), which operates at background pressures less than 10-9 Torr and utilizes a bimodal carbon fiber cathode and pyrolytic graphite anode, is used to validate simulation results. Additionally, the vircator at TTU is capable of changing the accelerating voltage, the anode-cathode (A-K) gap distance, and the distance of the cavity backwall relative to the position of the A-K gap on the fly without breaking tube vacuum, all in an effort to achieve greater frequency tunability and output power. However, this creates a very large, time-intensive experimental parameter space and makes a simulation model attractive for exploring additional output capabilities. ICEPIC results from a large combination of A-K gap distances, backwall distances, driving voltages, and cavity diameters are presented and compared to experimental results, highlighting frequency tunability of the system from a single tube.

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+ Graph Partitioning-Based Zonal Reserve Allocation For Congestion Management In Power Systems With Wind Resources
  S. Abedi; M. He; M. Giesselmann
Abstract:  Real-time actuation of scheduled reserve capacity in power system operations with high penetration of wind power is prone to failure on account of unexpected shortcomings in network transfer capability. In this paper, a graph partitioning-based reserve zoning method is incorporated into the security-constrained unit commitment to improve the deliverability of operating reserves in a reserve zone and mitigate possible congestions caused by uncertain wind power. A graph representation of power system is proposed in which the edge weights are quantified by the likelihood of secure transmission utilization for each line. The probability distribution of line flows are characterized by the uncertainty of multiple correlated wind farm output forecasts as well as credible line outage contingencies reflected on the line flows using distribution factors. The minimum k-cut problem using the Gomory-Hu equivalent tree is addressed as a simple and efficient method to solve the NP-complete partitioning problem. The resultant zones can assure reduced risk of congested operating conditions and thus, provide a new approach to efficient management of intra-zonal congestions.

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+ High Electric Field Atmospheric Breakdown Of Air At High Frequency For Large Gaps
  A. R. Chowdhury; H. K. Nguyen; R. P. Joshi; J. C. Dickens; J. J. Mankowski; A. A. Neuber
Abstract:  Summary form only given. Breakdown of air at atmospheric pressure in high frequency uniform electric fields and large gaps is discussed. In the high frequency band of a few MHz to few tens of MHz, the breakdown threshold voltage is lowered from its DC value due to enhanced space charge from ions that become trapped in the gap.1 While there is some literature concerning breakdown in this frequency range, it does not consider gaps larger than 1 cm.2A fluid model is developed to simulate plasma development in a baseline 6 cm gap primarily to explore power limitations for high power, electrically small antennas, which are operated cw at MHz frequencies. The ion densities are obtained from a drift-diffusion model, though data for the ionization, electron collision, and attachment parameters were obtained from Monte Carlo simulations, while ion diffusion and drift velocities were taken from the literature. As expected, the Monte Carlo simulations reveal that the EEDF follows any change in the electric field on the picosecond timescale at atmospheric pressures, much faster than any variation due to the externally applied electric field. Results from the simulation for gap lengths varying from the 6 cm baseline and air pressures are obtained, analyzed, and also compared with available reports.3

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+ Limitations Of Bulk Sic Photoconductive Semiconductor Switches, And Evaluation Of Pin Sic Photoconductive Semiconductor Switches
  D. L. Mauch; V. E. Meyers; R. P. Joshi; A. A. Neuber; J. C. Dickens
Abstract:  A comprehensive picture of the relationship between optical fluence, optical wavelength, system load, and photocurrent efficiency (PE) in SiC photoconductive semiconductor switches (PCSSs) is presented. Variation of the optical wavelength (300-380 nm) and optical fluence (0.2-200 J m-2) was accomplished with a Nd:YAG pumped optical parametric oscillator (7 ns FWHM) and a broadband variable attenuator. The PE was found to typically be in the range of 1-2 %, depending on wavelength, and the bulk PCSS on-state voltage driven by external circuit parameters. Features of the high electric field stress behavior (> 200 kV/cm) of the bulk PCSS were captured with high fidelity in a 1D drift-diffusion model with a self-consistent Poisson solver including trap assisted tunneling, Poole-Frenkel, and barrier lowering with enhanced tunneling effects. In addition, trap to band impact ionization as well as Coulombic and repulsive trapping potentials were included.

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+ Operation And Maintenance Cost Optimization In The Grid Connected Mode Of Microgrid
  S. Ramabhotla; S. Bayne; M. Giesselmann
Abstract:  A microgrid integrated with Distributed Energy Resources (DERs), Energy Storage, and Controllable Loads along with critical and non-critical loads is considered. The operation and maintenance cost (O&M) optimization is performed by the Economic Dispatch using the Reduced Gradient Method in the grid connected mode of microgrid. The minimized cost function of the system must be obtained for the optimization of the O&M cost of microgrid while meeting the load demand. The O&M cost includes the operation and maintenance cost of generated energy by each source and also the energy purchased from the utility. For obtaining the minimum cost of the system, the reduced gradient algorithm is implemented. To improve the reliability and to enhance the economic dispatch operation, a diesel generator and a battery energy storage are included in the microgrid. Different scenarios of the energy sources are compared along with the change in wind and battery profiles of microgrid to obtain the minimum O&M cost of the system. Various profiles of battery and wind energy are considered and minimal O&M cost of each profile is obtained and compared. As a result, the optimal cost of the system is obtained by considering the change in wind and battery profiles and hence provides the optimal solution while meeting the critical and non-critical loads demand.

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+ Optical Nonlinear Absorption Characterization Of Bulk Semi-Insulating 4H-Sic At And Above The Band Edge
  V. Meyers; D. Mauch; J. MaÅ„kowski; J. Dickens; R. Joshi; A. Neuber
Abstract:  Nonlinearity of optical absorption in semi-insulating bulk 4H-SiC has been investigated. Of interest was the optical bleaching behavior of 4H-SiC at and just above the band edge in the range 3.11-3.33 eV (wavelength 380-355 nm). Results of experiments on 200 μm and 490 μm thickness samples indicate partial bleaching in the optical fluence range from 70 W/cm2 to 1.8 kW/cm2, and the absorption coefficient was found to vary by approximately 10% within this range. These experimental findings are supported by simulation results obtained from a first order semi-empirical rate based model linking excitation-induced change in density of states with the absorption coefficient over the range of tested power densities. As expected, this effect scales with photon energy. Characterization of 4H-SiC absorption behavior under varying fluence will aid in design optimization of a Photoconductive Semiconductor Switch (PCSS).

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+ Particle-In-Cell Modeling Of A Reflex-Triode Vircator Using Icepic
  P. M. Kelly; J. Dickens; A. Neuber; J. J. Mankowski
Abstract:  This study describes a three-dimensional particle-in-cell (PIC) simulation for a reflex-triode virtual cathode oscillator (vircator). In particular, these efforts have focused upon the development of a robust, consistent model using the ICEPIC (Improved Concurrent Electromagnetic Particle-In-Cell) code from the Air Force Research Laboratory (AFRL). The vircator operates at background pressures less than 10-9 Torr and utilizes a bimodal carbon fiber cathode and pyrolytic graphite anode. Experimental data from the hard-tube vircator at Texas Tech University (TTU) is used to validate simulation results. A working, three-dimensional model of a reflex-triode vircator allows for better understanding of the physical processes responsible for microwave generation and thus enables the development of a more efficient and more customizable system. Simulation results detail the virtual cathode formation and the subsequent extraction of radiated microwave energy. Rather than relying on a non-directional isotropic radiation pattern for the radiated power, the true effective radiated power (ERP) from a three-dimensional, frequency-dependent radiation pattern has been extracted from the ICEPIC model. Furthermore, contributions from higher-order modes, particularly in the upper C-band regime, lead to frequency hopping and decreased microwave output power. Simulated results aid in identifying mode contributions and developing schemes to minimize contributions from undesirable modes. ICEPIC results are presented and compared against experimental results at several different operating conditions.

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+ Pulsed Characterization Of A Uv Led For Pulsed Power Applications
  N. A. Wilson; D. L. Mauch; J. C. Dickens; A. A. Neuber
Abstract:  Summary form only given. The electrical and optical characteristics of a high power UV LED (365 nm wavelength) were evaluated under pulsed operating conditions for pulsed power applications. Measurements were made over varying pulse width (30 ns-100 μs), current (0 A-250 A), repetition rate (single shot -1 MHz), and temperature (23° C-80° C). Diagnostics used included a calibrated photodiode operating in the linear regime for transient optical power measurements, a grating / high speed ICCD based spectrograph for transient spectral analysis, and multiple 10:1 standard oscilloscope probes configured differentially for electrical measurements. A red shift was observed in the output spectrum of the LED with increasing temperature and increasing pulse-width. LED forward voltage was observed to increase linearly with increasing current (≈ 3.5 V-5.2 V) and decrease with increasing pulse-width. The peak optical power observed was > 13 W and a maximum efficiency of 22 % was observed. The evaluated LED and auxiliary hardware were successfully used as the optical trigger source for a SiC photoconductive semiconductor switch (PCSS) under high impedance conditions.

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+ Pulsed Power Evaluation And Simulation Of High Voltage 4H-Sic P-Type Sgtos
  A. Ogunniyi; H. O'Brien; M. Hinojosa; J. Schrock; S. Lacouture; E. Hirsch; S. Bayne; Sei-Hyung Ryu
Abstract:  Future Army pulsed power applications semiconductor devices that will meet requirements for high-power, low weight and volume, and fast switching speed. The following paper presents the pulsed power evaluation of high voltage silicon carbide (SiC) super gate turn-off (SGTO) thyristors. These devices are well suited for high voltage, high temperature pulsed power and continuous power electronic systems. A pulse-forming network (PFN) circuit and a low inductance, series resistor-capacitor (LRC) circuit were developed to evaluate both the fast dI/dt capability and the pulse safe operating area (SOA) of the SiC SGTO. Transient simulations of the high voltage SiC SGTOs were also performed on a narrow pulse LRC circuit to investigate the device's switching behavior under extreme pulsed conditions.

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+ Reflex Triode Vircator Design For Extended Frequency Tuning Capabilities
  C. Lynn; D. Barnett; K. Rainwater; A. Neuber; J. Dickens; J. Mankowski
Abstract:  A stand-alone vircator based high power microwave system has been designed as an effects test source. The goal of this system is to cover the frequencies from 4.0 GHz to 6.0 GHz. To date a working prototype has been manufactured and field tested. The current system is capable of producing microwaves at frequencies of 4.06, 4.27, 4.45, 5.83, 5.95 and 6.06 GHz at field levels in excess of 100 kV/m, measured at 3 meters. Additionally, the source and all subsystems are capable of burst mode operation for a duration of 2 s at 500 Hz pulse repetition frequency (PRF). The wide range of tunability was achieved by varying the A-K gap as well as the location of the A-K gap inside the cavity. The A-K gap is varied by a bellows sealed linear actuator which is attached to the cathode. The position of the A-K gap within the cavity is altered by moving a liner and microwave reflector (which form a cavity) within the main vacuum tube. However, the experimentally observed frequencies obtained with the current system leaves a gap from 4.45 to 5.6 GHz. In order for the test system to produce microwaves within this frequency range, a new tube is under development. The cavity of the new tube has a smaller cavity which should push the resonant frequencies into the desired range (from 4.45 GHz to 5.6 GHz). This presentation discusses the experimental results obtained with the new tube and compares that with the previously built and tested source.

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+ Reliability Optimization Using Fault Tree Analysis In The Grid Connected Mode Of Microgrid
  S. Ramabhotla; S. Bayne; M. Giesselmann
Abstract:  In a microgrid, PTC Wind Solutions is used toimplement the optimization of reliability with the help of FaultTree Analysis (FTA). The reliability of each energy source alongwith the non-critical load is calculated. To interpret the faulttree results, the quantitative and qualitative analysis arecalculated. Then the importance measures like RiskAchievement Worth, Risk Reduction Worth, CriticalityImportance and Fussel -- Vesely Importance are used tocalculate the sensitivity and uncertainty of fault tree results. Thecomponents which are sensitive and at high risk are calculatedfrom the results. Using the logic gates in the PTC WindchillSolutions, the entire fault tree for a non-critical load outage isbuilt and studied. From the results, the unreliability andunavailability of the fault tree are used to calculate thereliability and availability of non-critical load outage. From theFault Tree Analysis, the unavailability and unreliability of noncriticalload outage are calculated which illustrates the values ofavailability and reliability. From the fault tree analysis, theunavailability and unreliability of non-critical load outage arecalculated as 0.01228, which illustrates that the availability andreliability as 98.77%. Minimal cut sets of circuit breaker acrossthe non-critical load, Point of Common Coupling at the maingrid, and a transformer are calculated from the QualitativeAnalysis. The top event probability evaluation of a non -- criticalload is performed using the Quantitative analysis whichindicates the system failure probability. The calculation ofImportance measures -- Risk Achievement Worth, RiskReduction Worth, Criticality Importance, Fussel -- VeselyImportance is performed. Thus, the reliability and availabilityof non-critical load is obtained using the PTC WindchillSolutions. The top event occurrence is caused by the basic andintermediate events of a fault trees. The components at high riskare calculated using the importance measures. Therefore, fromthe Qualitative and Quantitative analysis the components whichare at high risk and sensitive are obtained and maintained wellto optimize the reliability.

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+ Silvaco Based Electro-Thermal Analysis Of 4H-Sic Tiv-Jfet Structure Under Extremely High Current Density Resistive Switching
  B. N. Pushpakaran; S. B. Bayne; A. A. Ogunniyi
Abstract:  A 2D model of a 1200 V normally-ON 4H-SÄ°C Trenched and Implanted Vertical Junction Field Effect Transistor (TIV-JFET) cell structure was designed and simulated using Silvaco ATLAS TCAD software to investigate and understand the effects of extremely high current density pulsed switching on the device characteristics. The JFET cell was designed for an active area of 2 μm2 and a threshold voltage of -7 V. Physics-based models were included to account for impact ionization, recombination effects, band gap narrowing, mobility and lattice heating. The electro-thermal simulation was performed using a resistive switching circuit at an ambient lattice temperature of 300 K. The circuit was designed for an ON-state drain current density of 5000 A/cm2. The device was simulated using a 100 kHz 50% duty cycle gate signal consisting of four switching cycles considering the simulation duration bottleneck. The analysis of lattice temperature profile revealed the formation of thermal hot spot in the channel area close to the gate P+ regions in the JFET structure. Further analysis showed an increase in the minority carrier concentration in the vicinity of the gate implants which affected the switching characteristics of the JFET at extremely high current density.

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+ Simulation And Design Trade-Off Analysis Of 15 Kv Sic Sgto Thyristor During Extreme Pulsed Overcurrent Conditions
  J. A. Schrock; E. A. Hirsch; A. Bilbao; S. Lacouture; W. Ray; S. Bayne; M. Giesselmann; A. Ogunniyi; H. O'Brien
Abstract:  Silicon carbide Super Gate Turn-Off (SGTO) thyristors are an advanced technology for increasing the power density of high voltage pulsed power or power electronic systems. However, the transient characteristics and failure modes of these devices have to be further understood. This paper presents the Atlas TCAD simulation of a 15 kV SiC SGTO thyristor during extreme pulsed overcurrent conditions. The simulated device is first validated against dc measurements of a physical device. The device is then simulated at various pulse current amplitudes using a 10 stage 100 μs PFN. In addition, a tradeoff study for the drift region and anode mesa width is performed.

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+ Simulation Study Of Switching-Dependent Device Parameters Of High Voltage 4H-Sic Gtos
  A. Ogunniyi; J. Schröck; M. Hinojosa; H. O'Brien; A. Lelis; S. Bayne; S. Ryu
Abstract:  The silicon carbide (SiC) "Super" gate turn-off thyristor (SGTO) is a viable device for high voltage and fast dI/dt switching applications. These devices are well suited for various pulsed power applications requiring high peak currents in the kilo-amp regime. The turn-on transition speed is determined by the spreading velocity, which depends on applied gate current, applied anode current density, minority carrier lifetime, and both the gate base-width and the drift region of the thyristor. The impact of device parameters on switching performance is discussed in this work.

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+ The Path To A Transportable Ionospheric Heater
  A. A. Neuber; D. L. Mauch; V. E. Meyers; B. Esser; R. P. Joshi; J. C. Dickens; J. J. Mankowski; T. M. Antonsen
Abstract:  A transportable ionospheric heater, TIH, research design is presented that will enable plasma studies of the ionosphere in latitudes that are presently inaccessible by fixed installations such as HAARP (High Frequency Active Auroral Research Program). The equatorial latitude with close to zero vertical magnetic fields is especially of interest for basic plasma physics studies as well as rf communication enhancement. To achieve a power level in the ionosphere of at least 70 dBW ERP in a footprint significantly smaller than HAARP the radiated power needs to be substantially increased. This minimum ERP is achievable in a 4 × 4 antenna array with 370 kW input power per element with about 25 m by 25 m footprint vs. HAARP's equivalent 365 m by 365 m (360 antenna elements total, 10 kW maximum per antenna). Maximum ERP, up to 95 dBW, may be achieved with the TIH on a 115 m by 70 m platform, a factor 17 reduced size from HAARP. Tunable, Electrically Small Antennas, ESAs are employed to overcome the maximum power limitations of the HAARP dipole based antennas. This demands a step-up from 10 kW to several 100 kW cw power in the 3 to 10 MHz band, which is required to effectively heat the ionosphere. Driving the ESAs necessitates a tunable rf source in the same power and frequency regime, where a more traditional rf tube or all solid state approach may be pursued. The focus of the driver related research has been on photoconductive solid state switching, PCSS, in a direct drive mode that incorporates the driver into the antenna itself. A full size ESA operating at 9.5 to 10 MHz has been demonstrated at 500 W cw power levels and ~ 90% efficiency, driven by a single SiC switch mimicking the full power PCSS operation. The challenges and physics limitations of scaling the switch, the tunable ESA antenna design, as well as their coupling are presented. The significant progress made towards a transportable ionospheric heater as it relates to the physics of the PCSS switching efficiency, electrical breakdown in the MHz regime in large gaps, lower power experiments, and numerical simulations is discussed.

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Publication Year:  2015
+ 1 Khz Rep-Rate Operation Of A Spark-Gap Switched Gyromagnetic Nonlinear Transmission Line Array
  Johnson, J; Reale, D; Barnett, D; Garcia, R; Cravey, W; Parson, J; Neuber, A; Dickens, J; Mankowski, J
Abstract:  This paper details the design, fabrication and performance of a coaxial ferrimagnetic nonlinear transmission line (NLTL), four element array, high power microwave (HPM) system operated at a 1 kHz repetition rate. Prime power is delivered from an 802L TDK Lambda power supply which charges a 5.2 nF capacitor bank up to -40 kV. The capacitors are discharged through a center pin trigatron spark gap. The trigger generator is optically isolated and battery powered for noise immunity and portability. It produces a 20 kV positive polarity pulse with a 20 ns risetime. The high dV/dt (1 kV/ns) is desirable to reduce jitter inherent to spark-gap switching. After the spark-gap switch has closed, the pulse is split four ways. The four pulses propagate through four adjustable delay lines for synchronization of the individual outputs. The four delay lines connect directly into four 76 cm NLTLs with NiZn ferrites where SF6 is the insulating dielectric. Each NLTL is terminated into a custom fabricated, Rexolite-filled, TEM horn antenna via a zipper balun. Lastly, a LabVIEW based control system automates the whole system using a National Instruments cRIO controller. Experimental observations will include in-line D-dot measurements of voltage waveforms and radiated D-dot field measurements.
+ A 2D Finite Difference Simulation To Investigate The High Voltage Blocking Characteristics Of 4H-Sic Photoconductive Semiconductor Switches
  Shaver, J; Mauch, D; Joshi, R; Mankowski, J; Dickens, J; Neuber, A
Abstract:  4H-SiC Photoconductive Semiconductor Switches (PCSSs) have shown significant promise for use in pulsed power related switch applications. This simulation uses the finite difference method, parallelized using a NVIDIA graphical processing unit and the CUDA framework, to solve the system of partial differential equations that model the semiconductor physics involved in the high voltage blocking state of the photoconductive switch. By taking into consideration material properties (mid-band gap trap energy level and concentration, etc.), we are able to gain an understanding of how changes in these parameters affect the space-charge-limited (SCL) currents observed in the high voltage blocking state. This subsequently allows for a fundamental understanding of the parameters controlling the high voltage switching capability of photoconductive switches. Results of the simulation are presented.
+ A Modular, High Rep-Rate, Fast-Risetime, Optically-Isolated, Pulse Trigger Generator
  D. H. Barnett; J. M. Parson; C. F. Lynn; P. M. Kelly; J. C. Dickens; A. A. Neuber; J. J. Mankowski
Abstract:  The paper presents the design and operational characteristics of an optically isolated, compact, modular pulse generator for spark-gap triggering applications. The pulse trigger generator is capable of operating at pulse repetition frequencies (PRFs) > 1 kHz for short bursts with variable pulse magnitudes and risetimes. The trigger generator utilizes a transformer, magnetic switch and an IGBT primary switch. It has been successfully used to trigger a trigatron-driven 10-stage, Marx generator driving a high power load. For portability and noise immunity, the trigger generator is optically isolated from its low voltage control and powered via a lithium ion polymer battery pack. A constant current dc-dc power supply charges the high voltage circuitry of the trigger generator and enables continuous operation with two modules. For operation, a large capacitor is initially charged and used as a buffer energy source. The intermediate charge storage in conjunction with a command-triggered MOSFET, provides the ability to quickly re-charge a trigger capacitor between each pulse of the burst. Circuit topology, experimental data, including voltage and current waveforms, and jitter of the overall system are discussed at various PRFs.

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+ A Simplified 2-D Fluid Model Of Plasma Formation Under Pulsed High Power Microwaves In Atmospheric Gases
  S. Lin; S. Beeson; Y. Li; C. Liu; A. Neuber
Abstract:  Summary form only given. The mechanism of plasma formation under high power pulse (HPM) excitation in gases (nitrogen and argon) at atmospheric pressures is studied utilizing a fluid model verified against experimental data. A 2-D approximation was introduced to model the cylindrically shaped gas volume and the associated electric fields. Thus, the fluid equations and Poisson equation for space charge effects are updated in x and y directions only (setting the gradient in the z-direction to 0). The goal of this numerical simulation was to accurately predict the plasma formation delay time under different gas types and pressures based on the calculated evolution of the plasma conductivity.An S-band TE111 resonator with a built-in quartz gas isolation tube in the center was fabricated1. A 4 MW, 4 μs pulse in the dominant TE10 mode provided by a 2.85 GHz magnetron propagates through it. In the fluid model, the effect of HPM on plasma formation is modelled with particle heating as well as elastic and inelastic collisions driven by the incident electric field in the vertical (normal) coordinate. The amplitude distribution of the HPM electric field is obtained from numerical simulation of the resonator using commercial EM software. Since the focus is on the onset of plasma formation, simulation is stopped before a large plasma density develops up to the moment when the transmitted power is reduced by 10% (-0.5 dB), which corresponds to an average plasma conductivity of 0.02 S/m. Both measurement and simulation cover a gas pressure range from 25 to 700 torr with delay times for N2 and Ar from 22 to 204 nanoseconds. The development of the particle densities and temperatures during the simulation is presented to reveal the dominant mechanism of plasma formation in atmospheric gases. The delay times for different gas types and pressures are in good agreement for low gas pressures (<; 200 torr). Deviations between the model and experiments at higher pressure are found to be primarily due to the onset of plasma filamentation.

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+ A Sparsified Vector Autoregressive Model For Short-Term Wind Farm Power Forecasting
  He, M; Vittal, V; Zhang, JS
Abstract:  Short-term wind farm power forecasting is studied by exploiting the spatio-temporal correlation between individual turbine's power output. A multivariate time series model for wind farm power generation is developed by using vector autoregression (VAR). In order to avoid the possible over-fitting issues caused by a large number of autoregressive coefficients and the impact on the forecasting performance of VAR models, a sparsified autoregressive coefficient matrix is constructed by utilizing the information on wind direction, wind speed and wind farm's layout. Then, the VAR model parameters are obtained through maximum likelihood estimation of real-time measurement data, by taking into account the sparse structure of the autoregressive coefficient matrix. The proposed approach is compared with univariate autoregressive models through numerical experiments, resulting in significant improvement, which is attributed to the turbine-level correlation captured by the developed VAR model.
+ A Wavelet Approach To Far-Field Signal Reconstruction Of Transient Electric Fields
  Eldridge-Looker, K; Fierro, A; Dickens, J; Neuber, A
Abstract:  Large antenna sizes present a severe limitation in the generation of low frequency signals. To alleviate this issue, a series of high frequency sources (and thus, smaller antenna sizes) may be combined to produce a lower frequency output in the far-field. This reconstruction technique applies to signals of arbitrary shapes in addition to frequency lowering. Due to the large parameter space, wavelet decomposition theory is coupled with particle swarm optimization to define appropriate time shifts and amplitude adjustments to the high frequency sources (wavelets) in order to synthesize an output signal with the desired frequency or shape. Fifteen individual high frequency wavelets (f = 1 GHz) are utilized in this application to produce a final output signal in the far-field of 600 MHz. The radiation of a single wavelet is simulated using a broadband Chebyshev TEM horn antenna in order to perform far-field constructive and destructive interference analysis of all 15 wavelet signals. Simulation of the TEM horn antenna shows reasonable wavelet signal fidelity with minimal reflections from the antenna aperture as the pulse is propagated to the far-field. Examination of the far-field electric field enables accurate temporal depiction of the reconstructed signal from the 15 pulsed sources at any given point in space. By adjusting the source array geometry, the location of the desired signal (determined by the particle swarm optimization) can be narrowed down to a single location. Overall, combining particle swarm optimization, wavelet decomposition theory, and electromagnetic wave propagation enables the accurate reconstruction of far-field temporal electric fields from the combination of 15 wavelet sources and verification of the desired signal location.
+ Analysis Of A Tunable Electrically Small Antenna
  Esser, B; Beeson, S; Dickens, J; Mankowski, J; Neuber, A
Abstract:  A tunable, metamaterial-inspired, electrically small antenna topology is evaluated for a possible future use as the principle radiating element in a mobile Ionospheric Heating (MIH) system. The RF source signal is fed via a 50 Omega coaxial cable into a small semi-loop antenna (SLA). This inductively couples to a capacitively loaded loop (CLL) providing a natural 50 Omega match to the source. The resonant frequency of the antenna can be adjusted by varying the capacitance of the CLL via inserting a large permittivity dielectric. A simplified circuit model is used to show that the resonant frequency can be tuned between 40 - 100 MHz. Also, the maximum power handling capabilities achievable with this antenna topology at frequencies relevant to ionospheric heating (similar to 10 MHz and below) are estimated.
+ Analysis Of Advanced 20 Kv / 20 A Silicon Carbide Power Insulated Gate Bipolar Transistor In Resistive And Inductive Switching Tests
  Bilbao, AV; Schrock, JA; Ray, WB; Kelley, MD; Bayne, SB
Abstract:  The power density of pulsed power systems can be increased with the utilization of silicon carbide power devices'. With the latest developments in manufacturing techniques, the fabrication of insulated gate bipolar transistor (IGBT) devices with blocking voltages as high as 20 kV are now possible(2). A complete practical understanding of ultra-high voltage silicon carbide device switching parameters is not yet known. The purpose of this research is to show switching parameters extracted from inductive and resistive switching tests performed on state of the art 20 kV silicon carbide IGBTs. Resistive switching tests were used to extract device rise time, fall time, turn-on delay, turn-off delay and conduction losses. Double pulsed inductive switching tests were used to extract turn-on and turn-off switching energies and peak power dissipation. The data was obtained at case temperatures from 25 degrees C to 150 degrees C.
+ Analysis Of Advanced 20 Kv/20 A Silicon Carbide Power Insulated Gate Bipolar Transistor In Resistive And Inductive Switching Tests
  A. V. Bilbao; J. A. Schrock; W. B. Ray; M. D. Kelley; S. B. Bayne
Abstract:  The power density of pulsed power systems can be increased with the utilization of silicon carbide power devices1. With the latest developments in manufacturing techniques, the fabrication of insulated gate bipolar transistor (IGBT) devices with blocking voltages as high as 20 kV are now possible2. A complete practical understanding of ultra-high voltage silicon carbide device switching parameters is not yet known. The purpose of this research is to show switching parameters extracted from inductive and resistive switching tests performed on state of the art 20 kV silicon carbide IGBTs. Resistive switching tests were used to extract device rise time, fall time, turn-on delay, turn-off delay and conduction losses. Double pulsed inductive switching tests were used to extract turn-on and turn-off switching energies and peak power dissipation. The data was obtained at case temperatures from 25 C to 150 C.

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+ Analysis Of Carrier Lifetime Effects On Hv Sic Pin Diodes At Elevated Pulsed Switching Conditions
  A. A. Ogunniyi; H. K. O'Brien; M. Hinojosa; L. Cheng; C. J. Scozzie; B. N. Pushpakaran; S. Lacouture; S. B. Bayne
Abstract:  Future Army power systems will require utilizing high-power and high-voltage SiC devices in order to meet size, weight, volume, and high power density for fast switching requirements at both component and system levels. This paper presents the modeling and simulation of a high voltage (>12kV) silicon carbide PiN diode for high action pulsed power applications. A model of a high power PiN diode was developed in the Silvaco Atlas software to better understand the extreme electrical stresses in the power diode when subjected to a high-current pulse. The impact of carrier lifetime on pulsed switching performance of silicon carbide (SiC) PiN diode was investigated.

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+ Analysis Of Cathode Emission Phenomena: Effects Of Barrier Thinning, Field Enhancements And Local Heating
  Majzoobi, A; Joshi, RP; Neuber, A; Dickens, J
Abstract:  Intense electron emission from cathodes that provide very high current densities (several kA/cm(2)) is necessary for a various pulsed power applications. This contribution presents a quantitative analyses of the following processes and inherent physics: (a) Local field enhancements at micro-protrusions, (b) role of ion/ions near the emitting surface in lowering and thinning the potential barrier which increases emission. (c) localized heating at cathode tips that could produce hot-electrons and hot-phonons, ultimately leading to localized melting. Temperatures are predicted to possibly reach the cathode melting point on the nanosecond time scales. This is in keeping with the explosive emission phenomenon that is well known.
+ Analysis Of Gan Power Mosfet Exporsure To Pulsed Overcurrents
  W. B. Ray; J. A. Schrock; A. V. Bilbao; M. Kelley; S. Lacouture; E. Hirsch; S. B. Bayne
Abstract:  The advancement of wide bandgap semiconductor materials has led to the development of Gallium Nitride (GaN) power semiconductor devices, specifically GaN Power MOSFETs. GaN devices have improved characteristics in carrier mobility and on-state resistance compared to Silicon solid state switches. With the development of these new power semiconductor devices a need was established to understand the behavior of the devices switching performance under stress, with regards to situations in pulsing circuits. Through the examination of the switching characteristics of GaN devices, the results can be used for the improvement of advanced pulsing circuit design with GaN solid state switches. In this paper the authors develop a test bed to expose the GaN Power MOSFETs to single and repetitive pulsed overcurrents. The test bed was developed using a Pulse Ring Down board in a radially symmetric configuration to minimize the total equivalent inductance and resistance. The test bed switches the GaN MOSFET with low impedance between the DC bus and ground to induce the stress the MOSFET experiences during pulsed overcurrents. The DC characteristics were measured between switching sets to reveal characteristic signs of potential degradation and failure modes due to pulsed overcurrents. The single and repetitive pulse switching characteristics are captured, analyzed, and shown.

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+ Battery And Wind System In Weak/Strong Grid Analysis
  A. S. Subburaj; S. B. Bayne
Abstract:  The paper provides an analysis of the performance of the battery (1MW/1MWh) and wind system (1.7MW) when connected to weak or strong grid. Understanding the performance of the battery and analysis of the battery system tied to the distribution grid with heavy penetration of wind as a function of the strength of the grid is discussed with the aim to understand the optimized energy flow between the battery, the wind farm, and the utility grid, energy management for storage, battery performance, energy dispatch and reliability. The advanced battery model utilizes the dual polarization electrical equivalent model for the analysis. The grid-connected battery and wind system simulation results are obtained using PSCAD software.

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+ Burst Mode Operation Of A High Peak Power High Pulse Repetition Rate Capacitor Charging Power Supply
  Holt, SL; Lynn, CF; Parson, JM; Dickens, JC; Neuber, AA; Mankowski, JJ
Abstract:  Fast capacitor charging is a power electronics application with unique challenges requiring both low voltage, high current operation and high voltage, low current operation from the same system at different points in the charge cycle. Such dynamically differing operating points create distinct challenges in obtaining high efficiency throughout a charge cycle. In addition, the power supply must be protected from negative voltage swings when attached to a high rep-rate power modulator. This paper presents the design and testing of a rapid capacitor charger designed for high rep-rate command charging of a Marx generator. The output stage uses a large inductor to delay discontinuous conduction during the early portion of the charge cycle and greatly improve efficiency. The design goals and tradeoffs will be discussed and simulation results will be compared to experimental data.
+ Characterization Of Intra-Bandgap Defect States Through Leakage Current Analysis For Optimization Of 4H-Sic Photoconductive Switches
  Thomas, D; Mauch, D; Dickens, J; Neuber, A
Abstract:  A method of characterizing mid-bandgap defect states in high purity semi-insulating 4H-SiC through leakage current analysis for optimization of SiC photoconductive switches is presented. The method utilizes two custom IV curve tracer systems to measure leakage currents through the material under various voltage/current conditions. The first system is used under low current conditions and is capable of measurements from 0 to 45 kV at currents ranging from 0 to 3 mA with pA resolution. A second system measures the transient discharge of a charged capacitor bank through the material. Due to power dissipation concerns, the second system is used for currents higher than 0.1 mA. Voltage/current measurements in this region (>0.1 mA) are of interest due to the information concerning defect states near the conduction band. These shallow defect states are detrimental to switching performance while offering little benefit to voltage hold-off. From the combined data of these two systems, characteristics of the defect states are extracted and presented. We further elucidate the effect of contact annealing temperature on shallow trap levels in electron-beam irradiated material (2*10(18) 1/cm(2)).
+ Characterization Of The Optical Properties Of Gan:Fe For High Voltage Photoconductive Switch Applications
  Meyers, V; Mauch, D; Mankowski, J; Dickens, J; Neuber, A
Abstract:  The optical properties of bulk semi-insulating GaN:Fe are obtained to assess its future suitability as a high voltage photoconductive semiconductor switch (PCSS). The material properties of GaN: Fe hold significant promise to improve devices for pulsed power and other applications. Growth techniques of bulk GaN: Fe, which have hitherto been largely insufficient for commercial applications, are nearing the point that anticipatory characterization research is warranted. In this paper, the optical constants of bulk GaN: Fe (refractive index, absorption coefficient, and off-state dielectric function) were determined by optical reflection/transmission analysis. The results of this analysis are compared with a similar treatment of bulk 4H-SiC as well as possible elements of PCSS housing: Sylgard 184 elastomer, and EFI 20003/50013 electrical potting epoxy. The data presented provide foundational material characterization to enable assessment of the feasibility of GaN: Fe as a practical high voltage PCSS material. Beyond basic materials research, these properties inform design optimization in PCSS construction and implementation.
+ Depth-Based Localization For Robotic Peg-In-Tube Assembly
  A. D. Udai; R. P. Joshi; S. K. Saha
Abstract:  Peg-in-tube assembly stands ahead of a more common benchmark task for industrial assembly, i.e., `pegin-hole'. The robot can easily be deceived to detect the actual hole while performing a `peg-in-tube' task as the tube has a surrounding pocket that cannot support the peg. The paper presents a thorough geometrical analysis of the `peg-in-tube' assembly process, and proposes a novel algorithm based on depth measurements of peg center to perform `peg-in-tube' task. The results are demonstrated on a KUKA KR5 Arc industrial robot with a chamferless cylindrical peg and a tube having a minimum clearance of 0.10 mm.

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+ Development Of Secondary Breakdown Circuit For Dv/Dt Analysis Of Sic Devices
  Schrock, JA; Ray, WB; Bilbao, AV; Kelley, MD; Hirsch, EA; Holt, SL; Bayne, SB
Abstract:  Silicon carbide (4H-SiC) is a leading option for increasing the power density of pulsed power and power electronic systems(1, 2). SiC devices used in high voltage switching applications experience high dV/dt due to fast switching transients. Under high dV/dt conditions the devices can exhibit spurious turn-ON. For SiC devices to achieve widespread acceptance the dV/dt limit must be established. To measure the dV/dt limit, a circuit comprised of four silicon avalanche BJTs operating in secondary breakdown was constructed. This circuit is capable of generating dV/dts well in excess of what SiC unipolar and bipolar devices might be exposed to in typical applications. Two SiC diodes in an OR configuration are used to perform a comprehensive dV/dt analysis as a function of dc bias. Using this experimental setup dV/dts up to 200 V/ns were applied to SiC MOSFETs, and the induced gate to source voltage was measured. Preliminary dV/dt results achieved with the secondary breakdown circuit are shown for a range of dc biases.
+ Di/Dt Evaluation Of A Si N-Type Gto Designed For Pulsed Power Applications
  T. Flack; C. Hettler; S. Bayne
Abstract:  Pulsed power systems which utilize solid state switching devices, rather than spark/gas-type devices, could potentially exhibit increased energy density, repetition rate, operational lifetime, and ruggedness. However, further evaluation of advanced solid state devices, such as thyristor type devices, is required to better understand their operation for pulsed power applications. This paper details experimental evaluation of the dI/dt capabilities of a silicon (Si) n-type, asymmetric-blocking gate turn-off thyristor (GTO) manufactured by Silicon Power. The device under test (DUT) is rated to block up to 4 kV with rated dI/dt of 30 kA/μs. The DUT was designed as a solid state replacement for spark/gas-type switching devices in pulsed power applications. A low inductance test circuit was designed and built to evaluate the dI/dt capabilities of the DUT. Specific care was taken to minimize the parasitic inductance and thereby exploit the achievable dI/dt ratings by the test devices. An external fiber-driven gate driver is used to trigger the device with gate current (IG) of approximately 1.3 A and rate of current change (dIG/dt) of approximately 25.5 A/μs. Experimental dI/dt values greatly exceeded rated values; specifically dI/dt values of approximately 77 kA/μs were readily achieved at 4 kV. No device degradation was observed over the course of evaluation.

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+ Economic Analysis Of Battery Energy Storage System
  W. B. Ray; A. S. Subburaj; J. A. Schrock; S. B. Bayne
Abstract:  Grid-connected battery energy storage systems (BESS) are essential for improving the transient dynamics of the power grid. There is ongoing research about how BESS integration with renewable energy sources can improve renewable energy deployment in the grid. However, the economic feasibility of BESS is a practical limitation of their integration into power systems. BESS costs include both the start-up costs of building the system and the operating costs. Optimizing the operation of the BESS to maximize operating profit would make the BESS more economically feasible to power system operators, and lead to smoother integration of BESS. This manuscript overviews a program tool that analyses grid connected BESS in real world situations and optimizes the operation of the battery system. Through the use of this tool, a better understanding of the economic feasibility of BESS is achieved.

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+ Employing Price-Responsive Pevs In Microgrid: Optimal Operations And Security Management
  Abedi, S; He, M; Fatemi, SM
Abstract:  Penetration of Plug-in Electric Vehicles (PEVs) parking lots into distribution systems and microgrids offers useful decision tools for improving energy management and operations of power systems. In this paper, with an objective to minimize the operation cost while subject to the system, unit and security constraints, a microgrid energy management scheme is proposed, by taking into account PEVs throughout the grid as distributed storage responsive to the nodal prices. The presented method comprises the ex-ante optimal dispatch to minimize the anticipated operation cost, followed by a near real-time dispatch to manage the violation of security constraints regarding any congestion and voltage limit in the microgrid. The second dispatch, as recourse to the ex-ante dispatch, aims to minimize the operation cost and the deviation from the ex-ante dispatch decisions, while any possible binding constraint occurred in the ex-ante dispatch is mitigated. Simulation results on a test microgrid system demonstrate that the presented scheme can effectively ensure secure and economic operations of the microgrid as well as the risk reduction of the ex-ante decisions.
+ Enhancements To The Short Pulse High Intensity Nanosecond X-Radiator (Sphinx) Pulsed Power System
  N. R. Joseph; M. E. Savage; J. C. Stephens; J. A. Lott; B. A. Lewis; R. D. Thomas; M. A. Torres; E. G. Holman
Abstract:  The Sandia National Laboratories SPHINX accelerator is used to study the response of electronics to pulsed x-ray and electron environments. The system consists of a Marx generator and an oil-insulated pulse-forming line with self-closing oil switches. SPHINX has a peak load voltage of 2 MV and an adjustable pulse width ranging from 3 to 10 ns. The previous pulsed-power system had reliability and triggering issues with the Marx generator and subsequent undesired variations in voltage output. SPHINX was upgraded to a new Marx-generator system that has solved many of the voltage-output fluctuation and timing issues. The new Marx generator uses recently developed low-inductance 100-kV capacitors and 200-kV spark-gap switches. This paper provides an overview of SPHINX while capturing in detail the design, characterization, and comparative performance of the new Marx generator.

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+ Evaluation And Comparison Of 1200-V / 285-A Silicon Carbide Half-Bridge Mosfet Modules
  Kelley, MD; Bilbao, AV; Ray, WB; Schrock, JA; Bayne, SB
Abstract:  Silicon Carbide (4H-SiC) is a state-of-the-art solution for increasing the energy density of pulsed power and power electronics. High power SiC MOSFET modules have only recently become commercially available; for widespread acceptance further device characterization and reliability testing is necessary. The purpose of this work is to establish and compare device characteristics for two SiC power modules. Of the two modules tested, one contained Cree die and the other Rohm die. The device characteristics presented for the two modules are switching losses (E-ON & E-OFF) and on-state resistance (R-DS(ON)). E-ON, E-OFF, and R-DS(ON) were measured at 25 degrees C and 125 degrees C. The R-DS(ON) of the two modules was determined to be approximately equal; however, the SiC module containing the Cree die yielded significantly lower turn-on and turn-off switching losses. The measurements presented in this work demonstrate SiC power modules are a leading solution for high energy density applications.
+ Evaluation And Comparison Of 1200-V/285-A Silicon Carbide Half-Bridge Mosfet Modules
  M. D. Kelley; A. V. Bilbao; W. B. Ray; J. A. Schrock; S. B. Bayne
Abstract:  Silicon Carbide (4H-SiC) is a state-of-the-art solution for increasing the energy density of pulsed power and power electronics. High power SiC MOSFET modules have only recently become commercially available; for widespread acceptance further device characterization and reliability testing is necessary. The purpose of this work is to establish and compare device characteristics for two SiC power modules. Of the two modules tested, one contained Cree die and the other Rohm die. The device characteristics presented for the two modules are switching losses (EON & EOFF) and on-state resistance (RDS(ON)). EON, EOFF, and RDS(ON) were measured at 25°C and 125°C. The RDS(ON) of the two modules was determined to be approximately equal; however, the SiC module containing the Cree die yielded significantly lower turn-on and turn-off switching losses. The measurements presented in this work demonstrate SiC power modules are a leading solution for high energy density applications.

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+ Evaluation Of Gan:Fe As A High Voltage Photoconductive Semiconductor Switch For Pulsed Power Applications
  Mauch, D; Dickens, J; Kuryatkov, V; Meyers, V; Ness, R; Nikishin, S; Neuber, A
Abstract:  Semi-insulating Gallium Nitride is evaluated as a candidate material for use as a high voltage photoconductive semiconductor switch (PCSS) for pulsed power applications. The GaN: Fe samples used for this investigation were commercially available, bulk, semi-insulating samples measuring 10 mm x 10 mm x 475 mu m. Their optical and crystallographic properties were determined utilizing cathodoluminesence, photoluminescence, RHEED, as well as microwave reflection techniques for carrier lifetime studies. Experimental results are presented elucidating the potential of GaN: Fe sustaining high potential differences in both lateral and vertical geometry devices. For instance, electric field hold-off exceeding 100 kV/cm was observed in lateral geometry with mm sized gaps. In addition, a process for the homo-epitaxial growth of GaN: Si was developed in order to facilitate the fabrication of high quality ohmic contacts. Lastly, experimental results evaluating the on-state performance and photocurrent efficiency of a GaN: Fe based PCSS are presented.
+ Extraction Of Safe Operating Area And Long Term Reliability Of Experimental Silicon Carbide Super Gate Turn Off Thyristors
  Lacouture, S; Schrock, JA; Ray, WB; Hirsch, EA; Bayne, S; Giesselmann, M; O'Brien, H; Ogunniyi, A; Scozzie, C
Abstract:  While Silicon Carbide (SiC) based power switching elements are starting to appear that are able to perform better than their Si counterparts in terms of voltage hold off, current density and operating temperature, the material is still relatively new in the semiconductor arena, and although new device designs are simulated extensively before being committed to fabrication, there is often a large discrepancy between actual device performance and simulated results. Manufacturers certainly carry out some electrical testing of these quasi experimental components, but there is a dearth of information pertaining to Safe Operating Area (SOA) and device longevity. Texas Tech University's Center for Pulsed Power and Power Electronics, in cooperation with Army Research Lab, has carried out extensive long term, high - energy testing of SiC Super Gate Turn Off Thyristors (SGTOs) produced by Cree Inc. To conduct this extremely high volume testing at high energy levels, an automated test bed was designed that pulses the devices for an arbitrary number of cycles and alternately switches the device to a low energy characterization system, with all waveforms and current - voltage characteristics recorded. Approximately 350,000 high energy cycles on various SGTOs have been recorded. From this large database of results, actual SOA at high cycle count (>> 10,000 pulses) has been extracted for the devices. With each cycle's waveforms recorded, and the devices' characteristics traced at chosen intervals, several distinct changes in these parameters have been found to inevitably herald the imminent failure of a device. The most common change is in the gate - anode junction, where curve traces show a leaking, almost resistive behavior immediately before the junction becomes forward biased. As the system is completely automated, and limits can be set to halt a test sequence upon being broached, several devices have been brought to the brink of failure - an event that is usually catastrophic, physically destroying the device - to be examined by the manufacturer.
+ Fast And Accurate Electro-Thermal Behavioral Model Of A Commercial Sic 1200V, 80 M Omega Power Mosfet
  Pushpakaran, BN; Bayne, SB; Wang, GY; Mookken, J
Abstract:  The superior electro-thermal properties of Silicon Carbide (SiC) as compared to silicon make them a viable candidate for high voltage and high frequency applications. Due to the relatively recent surge in commercially available SiC power MOSFETs, there is an immediate demand for accurate simulations models to predict device behavior and aid circuit design process. This paper discusses the development of an accurate SPICE based model for a commercially available 1200V, 20A SiC power MOSFET manufactured by CREE Inc. based on the Enz - Krummenacher - Vittoz (EKV) MOSFET model. The advantage of using EKV model over the simplified quadratic model is the ability to characterize MOSFET behavior over weak, moderate and strong inversion regions with a single equation. The model was developed using parameters extracted through experimental data conducted at wide temperature range. Package parasitic components have been incorporated into the model to predict device behavior in high frequency switching applications. The model was simulated for its static and transient behavior and compared with actual device results to determine accuracy over a wide operating range.
+ Fast And Accurate Electro-Thermal Behavioral Model Of A Commercial Sic 1200V, 80 Mî© Power Mosfet
  B. N. Pushpakaran; S. B. Bayne; G. Wang; J. Mookken
Abstract:  The superior electro-thermal properties of Silicon Carbide (SiC) as compared to silicon make them a viable candidate for high voltage and high frequency applications. Due to the relatively recent surge in commercially available SiC power MOSFETs, there is an immediate demand for accurate simulations models to predict device behavior and aid circuit design process. This paper discusses the development of an accurate SPICE based model for a commercially available 1200V, 20A SiC power MOSFET manufactured by CREE Inc. based on the Enz - Krummenacher - Vittoz (EKV) MOSFET model. The advantage of using EKV model over the simplified quadratic model is the ability to characterize MOSFET behavior over weak, moderate and strong inversion regions with a single equation. The model was developed using parameters extracted through experimental data conducted at wide temperature range. Package parasitic components have been incorporated into the model to predict device behavior in high frequency switching applications. The model was simulated for its static and transient behavior and compared with actual device results to determine accuracy over a wide operating range.

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+ Gas Selection And Flow Optimization For A 1 Khz Trigatron Spark Gap
  W. H. Cravey; D. V. Reale; R. S. Garcia; J. M. Johnson; A. A. Neuber; J. C. Dickens; J. J. Mankowski
Abstract:  This paper discusses the design of a gas flow system for a 1 kHz repetition rate trigatron based spark gap. The system requires a flow rate high enough to clear the gas from the gap in under 1 ms while also maintaining the required operating pressure. The gap is a trigatron based design with an alumina insulated tungsten trigger pin. A 20 kV positive polarity pulse, with a 20 ns risetime, is applied to trigger the main gap which is charged to -40 kV. A brass guard ring is employed to shield the walls of the containment structure from contaminants in order to achieve a longer operational lifetime. Dry air and Nitrogen gasses are tested at various pressures and flow rates. Design considerations, such as inlet and outlet sizing and gap geometry, are taken into account to ensure a high air flow is achieved between the electrodes.

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+ Implementation Of A Battery Management And Protection System For High Power Pulsed Applications
  Cordero, E; Holt, S; Dickens, J; Neuber, A; Mankowski, J
Abstract:  High power pulsed systems often require high current 3-phase electrical service or large generators to meet prime power requirements, limiting the portability of the systems. A high power battery system offers a useful alternative for mobile applications. Of all battery chemistries, Lithium-ion polymer (LiPo) has become popular in consumer electronics due to its high energy density, low self-discharge rate and lack of memory. Unfortunately, the chemistry still has limitations. Overcharging or overheating of a LiPo cell may result in ignition and over-discharge can destroy the cell. To prevent these hazards, overcharge and undercharge conditions must be monitored at the cell level rather than the battery level because the charge and discharge efficiency varies from cell to cell causing cell voltages within a battery to diverge during normal operation. A battery management system designed to monitor and maintain a large battery designed for pulsed power applications is presented in this poster. The design of this battery management system is presented and its implementation in a multi-cell, high voltage battery capable of high current pulsed operation. A hazard analysis of high power batteries and the implemented safety system is also provided.
+ Initial Testing Of A Reflex Triode Vircator With Adjustable A-K Gap And Cavity Reflector
  Lynn, CF; Parson, JM; Kelly, P; Barnett, DH; Neuber, AA; Dickens, JC; Mankowski, J
Abstract:  Virtual cathode oscillators (vircators) can be easily tuned by altering the current density of the electron beam. This can be accomplished by changing the voltage applied to the a-k gap, or by physically changing the gap separation. Previous results with an adjustable a-k gap vircator achieved discrete tuning at frequencies of 1.5 GHz, 2.1 GHz, 4.1 GHz, 4.6 GHz, and 5.9 GHz. To achieve better tunability an adjustable cavity reflector was incorporated into the vircator design. Initial testing of the new vircator design has shown increased output power, as well as the ability to greatly increase the number of frequencies that can be tuned. Sweeping the A-K gap with the cavity reflector in two positions yielded 10 different frequencies of operation. Also sweeping the cavity reflector with the a-k gap set at 8.0mm yielded another unique frequency. Currently 11 unique frequencies have been identified, and the peak field measured from this vircator increased from similar to 40 kV/m to similar to 69 kV/m (> 70% increase in field). This paper illustrates the design of the vircator and presents some of the microwave data obtained. Additionally, a summary of all of the frequencies obtained and the peak field measured are included.
+ Investigation Of Charge Injection Threshold Field In Epoxy Resin
  He, M; Qiang, DY; Liu, N; Chen, G; Lewin, PL
Abstract:  In this paper, space charge formation in epoxy resin has been measured at different applied electric fields using the pulsed electroacoustic technique to reveal the charge injection threshold field. The influence of electrode material on the charge injection has also been investigated. It has been found that the threshold field value for negative charge injection is much lower than that of positive charges, and electrons are the dominant type of charge carrier in epoxy resin. Compared with aluminium, the sample with gold electrode shows a higher threshold field value and lower amount of charge injection. This observation can be attributed to a higher work function of the gold.
+ Line Transfer Margin-Based Congestion Management With Multi-Correlated Wind Power
  He, M; Abedi, S; Boker, A
Abstract:  Security-constrained unit commitment is studied by taking into account multiple correlated wind sources and the deliverability of operating reserves in a reserve zone. A power transfer margin for each transmission line is incorporated into the unit commitment problem, so as to mitigate possible congestions caused by uncertain and non-dispatchable wind power. Specifically, the power transfer margins of transmission lines are determined by utilizing the probabilistic information of multi-locational wind power generations, and by considering credible line-outage contingencies. The power transfer margins collectively guarantee that congested operating conditions occur with a reduced probability, and thus provide a new approach to the efficient management of intra-zonal congestions. The effectiveness of the proposed approach is verified through case studies on IEEE RTS-96, with comparisons to unit commitment with conventional reserve zone management.
+ Physics Based Electro-Thermal Transient Simulation Of 4H-Sic Jbs Diode Using Silvaco Atlas
  B. N. Pushpakaran; S. B. Bayne; A. A. Ogunniyi
Abstract:  The unique design of Silicon Carbide (SiC) Junction Barrier Schottky (JBS) diode has proved its superiority over silicon in the field of high energy density pulsed power applications. JBS diode design enables the development of high blocking voltage silicon carbide rectifiers with low ON-state voltage drop, low leakage and negligible reverse recovery. In pulsed power applications, devices get driven above their rated current carrying capacity for a transient duration. Under this scenario, it becomes critical to have a thorough understanding of the electro-thermal behavior of the device under pulsed condition. This research focuses on the design and simulation of a 4H-SiC JBS diode structure in Silvaco ATLAS software under steady state and pulsed conditions. Physics based models were incorporated to account for drift diffusion process, mobility, impact ionization and lattice heating. The JBS diode was designed for a blocking voltage of 3.3 kV and an ON-state current density of 100 A/cm2. A schottky barrier height of 1.1 eV was selected for the device. An array of interdigitated P+ regions with optimized separation was designed to shield the schottky interface from the high blocking electric field without affecting the ON state characteristics. The simulation results were used to analyze breakdown electric field distribution, forward current conduction path, switching performance and areas of localized lattice heating. The diode structure was simulated under pulsed condition pertaining to 500 A/cm2 current density and the lattice temperature profile was analyzed to identify the formation of thermal hot spots in the device lattice and possible failure mechanism. The JBS diode structure was simulated for its reverse recovery at varying magnitudes of turn OFF di/dt for an ON-state current density of 100 A/cm2.

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+ Protective Networks For High Voltage Power Supplies For Pulsed Power Loads
  M. G. Giesselmann; A. Bilbao
Abstract:  We are reporting on a comprehensive study on protective de-coupling networks for High Voltage (HV) pulsed power charging supplies. Typically HV power supplies charge large capacitor banks [1, page 3], [2, page 4], which are rapidly discharged into a pulsed power load. Even during a normal discharge, this can put severe stress on the power supply if it is not properly decoupled from the load. A fault at the load capacitor such as a flashover resulting in a ringing discharge with voltage reversal would put even more stress on the power supply, since the load capacitor could discharge through the rectifier diodes in forward direction. In such a case the output rectifier of the power supply could be instantaneously destroyed. Protective networks between the power supply and the load can prevent such damage but may limit the efficiency as well as the available power output and rep-rate of the HV power supply. We are reporting on a number of protective networks including combinations of resistors, inductors, and diodes that can be placed between the output of the power supply and the load. We are also considering the effects of parasitics and the surge I2t action integral [3, Page 20] of the output rectifiers of the power supply to arrive at guidelines for optimal system protection.

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+ Reliability-Constrained Self-Organization And Energy Management Towards A Resilient Microgrid Cluster
  M. He; M. Giesselmann
Abstract:  Microgrids, as individual controllable entities that can operate either islanded from or interconnected to main power grid, have emerged as a promising solution to improving energy efficiency and resilience to disturbance. When linked together in a self-organized manner, a cluster of microgrids can significantly enhance the reliability and power quality for critical load. With this insight, we study the self-organization and decentralized energy management of a microgrid cluster islanded from main grid after a disruptive event. In the self-organization stage, depending on the available generation resources, each microgrid decides on whether to connect to the cluster; and the microgrid energy management systems then "negotiate" on the optimal power exchange with each other in the cluster. Once the power exchange is determined, the generation and storage resources of each microgrid are managed to guarantee the energy reliability of critical loads and overall energy efficiency, through a scheduling procedure followed by a dispatch procedure. The effectiveness of the proposed method is revealed via case studies.

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+ Repetitive Operation Of A Megawatt Class Reflex-Triode Vircator
  J. M. Parson; C. F. Lynn; D. H. Barnett; S. L. Holt; P. M. Kelly; J. C. Dickens; A. A. Neuber; J. J. Mankowski
Abstract:  Repetitive operation of high-power microwave (HPM) sources is primarily restricted by thermal properties of anode and cathode materials. Note that even in single shot operation, vircators generally inject undesired plasma from the anode/cathode surfaces under high current densities, leading to excessive heating of electrode materials, vacuum degradation and impedance collapse that may ultimately lead to cut-off of microwave power. Heating of the anode and cathode materials during repetitive operation intensifies these problems and will cause accelerated erosion and/or permanent damage of the anode and cathode surfaces, especially when metallic electrodes are used. Hence, the vircator herein utilizes a carbon fiber cathode and a pyrolytic graphite anode. This paper elucidates the heating of the anode and cathode, and their spectrally resolved black-body radiation properties during repetitive operation.

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+ Solid State Linear Transformer Driver (Ltd) Development For Hpm Sources
  Collier, L; Walls, MB; Dickens, J; Mankowski, J; Neuber, A
Abstract:  The Marx pulse generator topology has been widely used in pulsed power applications(1,2). Another pulse generator topology, the linear transformer driver (LTD), has been developed3 that may serve as a viable alternative to the Marx generator. LTDs utilize inductively added stages to achieve high voltages and currents. Unlike a Marx generator, each stage in an LTD features multiple bricks, all of which are ground referenced and allow current to be distributed amongst an arbitrary number of switches. This allows for LTDs that utilize solid-state switches, potentially resulting in more compact and reliable pulse generators. A solid-state, >10 kA peak current, multiple-stage LTD is developed. The generator's performance will be analyzed for viability as a replacement for driving a high power microwave generator.
+ Subsynchronous Oscillation Detection Using Phasor Measurements And Synchrosqueezing Transform
  M. He; S. Nimmagadda; S. Bayne; M. Giesselmann
Abstract:  In this paper, a novel scheme for subsynchronous oscillation detection and modal parameter estimation is proposed, by leveraging the rich information contained in high-rate phasor measurements as well as the effectiveness of synchrosqueezing transform for multimodal signal analysis. Specifically, an instantaneous time-frequency representation of a voltage/current signal is first obtained by applying synchrosqueezing transform to the real-time data collected by a phasor measurement unit. The non-zero synchrosqueezing transform coefficients quantify the undamped frequency components of the original voltage/current signal at each time instant. For an unknown number of undamped frequency components, unsupervised clustering is applied to the non-zero synchrosqueezing transform coefficients in the frequency domain, so as to determine how many modes comprise the signal, as well as which mode each non-zero synchrosqueezing transform coefficient belongs to. Then, for each detected mode, the corresponding non-zero synchrosqueezing transform coefficients are utilized to reconstruct a component of the original voltage/current signal. Finally, the magnitude, damping factor and phase angle of each mode are estimated by applying a least square estimation algorithm to the reconstructed component signal. The effectiveness of the proposed approach is revealed through several case studies using IEEE benchmark models. Further, practical issues involving missing data, measurement noise and transform basis functions are also systematically addressed in this study.

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+ Suitability Of N-On Recessed Implanted Gate Vertical-Channel Sic Jfets For Optically Triggered 1200 V Solid-State-Circuit-Breakers
  Veliadis, V; Steiner, B; Lawson, K; Bayne, SB; Urciuoli, D; Ha, HC
Abstract:  A requirement for the commercialization of power SiC transistors is their long term reliable operation under the hard switching conditions and high temperatures encountered in the field. Normally-ON 1200 V vertical-channel implanted-gate SiC JFETs, designed for high-power bidirectional (four quadrant) solid-state-circuit-breaker applications, were repetitively pulse hard switched at 150 degrees C from a 1200 V blocking state to an on-state current of 115 A, which is in excess of 13 times the JFET's 250-W/cm(2) rated current at 150 degrees C. The JFETs were fabricated in seven photolithographic levels with a single masked ion-implantation forming the p+ gates and guard rings, and with no epitaxial regrowth. The pulsed testing was performed using a low inductance RLC circuit. In this circuit, energy initially stored in a capacitor is discharged in a load resistor through the JFET under test. The JFET hard-switch stressing included over 2.4 million 1200-W115-A hard-switch events at 150 degrees C and at a repetition rate of 10 Hz. The peak energies and powers dissipated by the JFET at each hard-switch event were 73.2 mJ and 68.2 kW, respectively. The current rise rate was 166 Alps and the pulse FWHM was 1.8 mu s. After over 2.4 million hard-switch events at 150 degrees C, the JFET blocking voltage characteristics remained unchanged while the on-state conduction slightly improved, which indicate reliable operation. An optically triggered solid-state-circuit-breaker, based on these rugged JFET, is proposed.
+ System Integration Of A Coaxial Ferrimagnetic Nonlinear Transmission Line Array
  R. S. Garcia; D. V. Reale; J. M. Johnson; W. H. Cravey; A. A. Neuber; J. C. Dickens; J. J. Mankowski
Abstract:  This paper describes the system integration of a four element, nonlinear transmission (NLTL) array. The HPM system components include a negative polarity 40 kV capacitor charging supply, a trigatron spark gap, a solid-state trigger generator, four delay lines with biasing coils, four coaxial ferrimagnetic NLTLs with biasing coils, eight dc current supplies, and four TEM horn antennas. A National Instruments cRIO FPGA based controller is used to interface the capacitor charging supply, the biasing coil power supplies and the trigger generator to a laptop based GUI. In order to minimize impact from EMI, all lines were properly shielded and the data acquisition equipment was located a sufficient distance away from the NLTL array. The GUI consists of options for controlling the current output on all 8 power supplies for biasing purposes, as well as pulse options that include repetitive pulsing based on the number of pulses or for a specific length of time. Pulse duration for the capacitor charger, the command charge, and the trigger can also be adjusted. An emergency stop button is included for safe shutdown of the trigger generator and all power supplies. A diagnostics setup is outlined describing the placement of inline coaxial D-Dot probes and a high voltage probe for laboratory testing.

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+ Zero Voltage Switching Multi Resonant Converter Using 0.6µm Technology
  A. Mishra; S. B. Bayne; Changzhi Li
Abstract:  Technology used for high performance DC-DC voltage regulator based Integrated Circuits is evolving. Zero voltage switching buck converter is one such DC-DC regulation schemes integrated in the power conversion circuitry and is designed such that power density is maximized and the switching losses are reduced. This paper discusses the design of AMI06 technology based zero voltage switching buck converter operating at 1 MHz switching frequency. A design example accommodating input voltage range from 5V"“8V DC at a constant DC output voltage of 3V was considered. The simulations were performed on Cadence tool to verify the feasibility of the proposed converter. Finally this zero voltage switching buck converter is compared to the conventional buck converter in terms of switching losses and efficiency.

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Publication Year:  2014
+ 10 Kv, 44 Ns Pulse Generator For 1 Khz Trigatron Reprate Operation Of Nltl
  J. M. Johnson; J. M. Parson; D. V. Reale; A. A. Neuber; J. J. Mankowski; J. C. Dickens
Abstract:  This paper presents a design and implementation of a 1 kHz, 10 kV, positively pulsed trigger generator with an average risetime of 44 ns for use in a coaxial ferrimagnetic Nonlinear Transmission Line (NLTL) High Power Microwave (HPM) system. The pulse trigger generator is based on two stacked 4 kV current-controlled n-type thyristors in a low inductance package capable of driving inductive loads with risetimes less than 200 ns. However, by implementing a magnetic switch this relatively is slow risetime is sharpened to tens of nanoseconds. The stacked boards allow for voltage addition at the output while maintaining the fast riestime.

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+ A Battery Powered 80 Kva Capacitor Charger
  S. Holt; E. Cordero; J. Mankowski; J. Dickens; A. Neuber; M. Scott; S. Calico
Abstract:  The design of a battery powered, rapid capacitor charger is discussed. The charger design is capable of an average output power of 80 kVA, for a burst time of roughly 5 seconds. Cool down time is required between bursts. A Lithium Ion Polymer (LiPo) battery pack with a nominal voltage of 355 V and fully charged open circuit DC voltage of 385 V will be used to power the rapid capacitor charger. The general topology of the charger is as follows. An IGBT H-bridge inverter uses pulse width modulation to create an AC waveform that is stepped up to a maximum of 58kV by a 1:170 ratio transformer. This high voltage output of the transformer is rectified and used to charge the capacitor bank.

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+ A Metamaterial-Inspired Electrically Small Antenna For Operation At 2 To 20 Mhz
  Gatewood, P; Neuber, A; Dickens, J; Mankowski, J
Abstract:  A metamaterial-inspired, efficient, electrically small antenna (ESA) is designed for the 2 to 20 MHz range, intended for use in a mobile Ionospheric Heating (MIH) system. The ESA consists of two main parts: a small semi-loop antenna (SLA), and an outer capacitively loaded loop (CLL). To increase the capacitance of the CLL and reduce the size of the ESA, a high permittivity dielectric is utilized. All designs were simulated in Ansoft HFSS with particular attention on radiation efficiency and bandwidth. The design aims for these ESAs are a high overall efficiency at dimensions much smaller than a wavelength.
+ A Modular High Power Battery System For Pulsed Power Applications
  E. Cordero; S. Holt; J. Dickens; A. Neuber; J. Mankowski; S. Calico; M. Scott
Abstract:  This paper presents the design of a scalable, high power battery system for pulsed power operations. The battery system is modular in design, with each module containing four Lithium Ion Polymer (LiPo) cells and a custom designed cell management board that actively monitors the voltage and temperature of each cell and also provides cell balancing functionality. The system is designed to be scalable by adding up to 25 modules in a series configuration. While the battery management system should be compatible with any lithium ion cells, this implementation uses 8 Ah capacity dual-core LiPo cells, rated for a 150 C discharge rate; allowing for a peak current output of 1,200 A. With 25 modules (96 LiPo cells) the system would have an open circuit voltage of 385 V and be capable of providing up to 1,200 A at 355 V for a peak output power of 420 kW. Special attention has been placed on safety features including overvoltage, undervoltage and temperature monitoring of every cell in the system. The charging/balancing system is capable of automatically shutting down if any of the voltages or temperatures exceeds established limits. The management circuitry is designed to have a low off-state power draw in order to maximize battery life when the system is not in use.

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+ A Wavelet Approach To High Power Microwaves
  Eldridge, K; Fierro, A; Dickens, J; Neuber, A
Abstract:  Wavelet decomposition and reconstruction are utilized to synthesize a high power microwave (HPM) signal at a frequency below the frequency of the employed radiating sources. Employing a larger number (on the order of ten) of smaller sources that produce short radiating pulses combined with appropriate amplitude scaling and shifting of the individual pulses enables the generation of a single waveform of longer duration. We describe the mathematical approach to the wavelet synthesis and give examples. For instance, an array of 10 sources, each producing a 0.5 ns pulse can be adjusted to generate a sinusoidal wave with a period of approximately 2 ns. The results of low power experiments are discussed in detail to demonstrate the practical feasibility of the wavelet approach.
+ Analysis And Review Of Grid Connected Battery In Wind Applications
  A. S. Subburaj; P. Kondur; S. B. Bayne; M. G. Giesselmann; M. A. Harral
Abstract:  This paper provides an overview of battery technologies and the grid-connected battery projects that integrate wind. It also discusses the deployment of a battery system at Reese Technology Center (RTC) in Texas. The research at RTC involves deploying energy storage devices (i.e. Batteries with grid-tie inverters) for application in wind farms to understand the interaction between wind energy, the grid and the grid loads. The research work focus on the modeling of a battery system and wind turbines when it is connected to the grid, with the aim to understand the optimized energy flow between the battery, the wind farm, and the utility grid, energy management for storage, battery performance, energy dispatch and reliability. With the view of modeling the test bed of the grid-connected battery project at Reese, this paper provides the preliminary simulation results using PSCAD on discharge characteristics of a single cell of a battery at various C rates.

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+ Analysis Of Dual Polarization Battery Model For Grid Applications
  A. S. Subburaj; S. B. Bayne
Abstract:  With worldwide growth of battery technologies in renewable energy production, the selection of battery model has become an important factor for a Battery Energy Storage System (BESS) to be deployed in a grid environment. It is essential to understand the battery type and the model, to achieve a coordinated control of the performance of BESS, Renewable Energy Sources (RES) and load management, including battery applications such as ramp control, frequency response, voltage response, emergency backup, transmission and distribution capacity utilization and peak load leveling, when connected to the grid. Recent studies showed that the battery capacity utilization is based on the battery discharge characteristics. In this paper, two types of battery models such as `stacked cell model' and `single cell model' of a 1 MWh Lithium Manganese Oxide (LMO) battery are taken into consideration to study the discharge characteristics. The approach is based on the use of the Dual Polarization Model (one of the Electrical Equivalent Circuit Models also called as Two Time Constant Model) in building the above mentioned battery models. The purpose of this paper is to build and simulate the battery models in Power Systems Computer Aided Design (PSCAD). Also the battery models are compared and analyzed on their performance during faults when connected to the resistive load at 1C discharge rate. The `single cell model' is constructed using the electrical equivalent circuit to build the 1 MWh battery module. In an attempt to simulate the `stacked cell model', initially one cell of the battery rated at 4.12 V, 60 Ah is modeled in PSCAD and then the cells are connected in series and parallel to build the model of 1 MWh battery module. The key results include the modeling of single cell and stacked cell models of the 1 MWh battery. The discharge characteristics of the battery models rated at 960V, 1200 Ah will be analyzed for the faults applied near the resistive load. The models will be tested for node compatibility, compilation issues and the response effectiveness when connected to the resistive load. Thus, the research paper will perform a comparative analysis of the simulation results of the two battery models in terms of discharge characteristics, speed, performance, stability and compatibility.

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+ Analysis Of Equivalent Circuit Of The Battery Connected To The Grid
  A. S. Subburaj; S. B. Bayne; M. G. Giesselmann; M. A. Harral
Abstract:  This paper provides an analysis of the equivalent circuit of the 1 MW battery tied to the grid. It also discusses the installation of a 1 MWh battery system at Reese Technology Center (RTC) in Lubbock, Texas. The research involves deploying energy storage devices for application in wind farms to understand the interaction between wind energy, the grid and the grid loads. A 1 MW/1 MWh battery storage system at the RTC is connected to the South Plains Electric Cooperative (SPEC) grid. The batteries are used for energy storage and for mitigation of transient conditions grid dynamics. In this paper the 1 MW battery is modeled in PSCAD and analyzed for its discharge characteristics when it is tied to the grid.

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+ Carrier Lifetime Measurement Of Silicon Carbide For Photoconductive Switch Applications Using An Ir Probe Laser
  White, C; Mauch, D; Thomas, D; Dickens, J
Abstract:  A system for measuring the recombination lifetime of high purity, semi-insulating (HPSI) 4H-SiC through transient free carrier absorption (FCA) for optimization of SiC photoconductive semiconductor switches (PCSS) is presented. The system measures the transient absorption of a continuous, low-power (<5mW) 1550 nm infrared probe laser. Free carriers were generated with both above and below bandgap illumination from the harmonics of a Nd:YAG laser (532 nm, 355 nm, and 266 nm - 10ns FWHM), and the carrier lifetime was numerically calculated from the absorption transient. High spatial resolution (similar to 10 um) was attained through the use of a high-precision, three-axis stage. The carrier lifetime measurements of various regions of several SiC PCSSs over varying levels of photo-excitation are presented.
+ Characterization Of Mid-Bandgap Defect States In 4H-Sic For Optimization Of Sic Photoconductive Semiconductor Switches
  Thomas, D; Mauch, D; White, C; Neuber, A; Dickens, J
Abstract:  A method of characterizing mid-bandgap defect states in high purity semi-insulating 4H-SiC through leakage current analysis for optimization of SiC photoconductive semiconductor switches, PCSS, is presented. The method utilizes two custom IV curve tracer systems to measure leakage currents through the material under various voltage/current conditions. The first system is used under low current conditions and is capable of measurements from 0 to 45 kV at currents ranging from 0 to 3 mA with pA resolution. While voltage/current measurements in the region >0.1 mA are of primary interest for quantifying defect states near the conduction band, standard IV measurements become difficult due to excessive power dissipation in the PCSS. Hence, a second system operating in transient mode is used for currents higher than 0.1 mA. This system measures the transient discharge of a charged capacitor through the PCSS, allowing for high current measurements while subjecting the material to high power dissipation for only a short period of time (milliseconds). It is the goal to extract from the combined data of these two systems characteristics of the defect states (concentration, energy level).
+ Comparison Study Of The Controllers For Grid Connected Battery System
  A. S. Subburaj; W. B. Ray; S. B. Bayne
Abstract:  This paper performs a comparison study on the performance of operation of a battery connected grid system with bi-directional grid-connected inverter and conventional PQ controller in steady state conditions. The deployment of a 1 MWh battery energy storage system (BESS) at Reese Technology Center (RTC) in Lubbock, Texas is described. The battery energy storage device was installed to further understand the interaction and performance of the battery within the power grid with the existing wind turbines at RTC as well as renewable energy sources and grid loads. The paper shows the simulation results obtained from PSCAD with the design of the different controllers. Compared with conventional PQ controllers, the bi-directional converter controllers greatly enhance the grid-connected converter's performance in the aspects of reduced power oscillations and increased operating stability.

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+ Deadline-Aware Concentration Of Synchrophasor Data: An Optimal Stopping Approach
  He, M; Zhang, JS
Abstract:  Deadline-aware concentration of synchrophasor data from spatially dispersed phasor measurement units (PMUs) is studied, with an objective to find the optimal policy for the wait time of a phasor data concentrator (PDC), such that the deadline-constrained synchrophasor data delivery from PMUs via PDC to control center achieves maximal expected throughput. When the statistical information on the communication latency from PMUs to PDC and from PDC to control center is known, the wait time problem is cast as a continuous-time optimal stopping problem. The optimal stopping policy is then shown to exist, and then obtained by utilizing the infinitesimal look-ahead rule under mild conditions. Further, the scenarios with substation PDCs or super PDCs are also considered. The dynamic wait time policy obtained by using the proposed optimal stopping approach, in comparison with two fixed wait time policies, results in significant improvement, as revealed through simulation studies.
+ Design And Operation Of A Fast-Risetime, 500 Hz, 24 Kv, Optically-Isolated Pulse Trigger Generator
  D. H. Barnett; J. Parson; C. Lynn; P. Kelly; M. Taylor; J. Dickens; A. Neuber; J. Mankowski; S. Calico; M. Scott
Abstract:  This paper presents the design and performance characteristics of an optically isolated, trigger generator for spark gap applications that is capable of operating at over 500 Hz rep rate. The pulsed trigger generator is designed to achieve fast risetimes on the order of 1kV/ns to cause breakdown between the trigatron trigger pin and the opposite electrode. The pulsed trigger generator is designed to trigger a 10-stage, 500 kV, 42 J Marx generator. The system is capable of delivering a 4"“25 kV pulse with a 10/90 risetime of 20 ns. A board was fabricated to control a capacitor charger and high voltage thyristor via fiber optic inputs. The capacitor charger, a 60 W constant current dc-dc power supply with variable voltage control, is capable of charging 1 nF in less than 0.3 ms. The system is battery-powered using a 33 V lithium polymer battery pack for isolated operation in noisy environments. For burst mode operation, a larger 250 nF buffer capacitor, which is initially charged, is connected through a 100 kΩ resistor to the trigger capacitor, which is varied between 1 and 40 nF. The value of the trigger capacitor is adjusted to provide optimum performance for a given transformer and magnetic switch. System modeling results along with experimental data are discussed including the reliability and performance of the overall system including jitter at 500 Hz operation.

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+ Digital Control Of A Rapid Capacitor Charger With Sensor-Less Voltage Feedback
  M. G. Giesselmann; A. Bilbao
Abstract:  We are reporting on a software implemented HV-sensor for a Digitally Controlled Rapid Capacitor Charger. The new contribution of this paper is to replace a physical voltage sensor with an algorithm that executes in real time in the digital controller for the charger. This avoids the cost, bandwidth limitations and insulation challenges of a conventional HV-sensor. The capacitor charger is controlled by a digital signal controller using a peak current mode control algorithm with adaptive slope compensation as reported in [1]. The peak current mode algorithm uses the analog comparator to detect the peak current and the duty cycle of the inverter at the current peak. Through knowledge of the current waveshape, we can deduct the charge that was transferred during each cycle. This information can be used to predict the voltage of the load capacitor during the charging process. To evaluate the feasibility of this approach, we compare the results from the capacitor voltage prediction algorithm to data obtained with a laboratory grade HV probe.

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+ Economic Dispatch Optimization Of Microgrid In Islanded Mode
  S. Ramabhotla; S. Bayne; M. Giesselmann
Abstract:  Microgrid combines with Distributed Energy Resources (DERs), energy storage, and controllable loads. It is connected to the maingrid through the point of common coupling (PCC). Economic dispatch using reduced gradient method is implemented for the optimization of energy in the microgrid using MATLAB. The optimization is obtained by minimizing the cost function of the system while meeting the load demand. The operation & maintenance cost, and investment costs are considered in the cost functions of the microsources. The minimum total cost of the system is obtained by comparing different scenarios of the microsources in the microgrid.

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+ Evaluation Of High-Voltage, High-Power 4H-Sic Insulated-Gate Bipolar Transistors
  M. Hinojosa; A. Ogunniyi; H. O'Brien; S. B. Bayne; C. Scozzie
Abstract:  This paper presents preliminary results on the static and dynamic characterization of 12 kV and 20 kV N-channel silicon carbide Insulated-Gate Bipolar Transistors (IGBTs). These state-of-the-art devices were evaluated for their possible use in pulsed-power and energy conversion applications. The 12 kV IGBTs had a chip area of 0.7 cm2 and were rated for 10 A. Their active area was 0.32 cm2, with a drift region of 140 μm and two different field-stop buffers of 5 μm and 2 μm. The 20 kV IGBTs had a chip area of 1 cm2 and were rated for 12 A. Their active area was 0.37 cm2, with a drift region of 180 μm, and their FSB was 2 μm. The switching and conduction losses were calculated for both devices with short pulses and low-inductance resistive loads. Both types of IGBTs displayed promising results for possible replacement of gas switches and Si IGBTs in high voltage applications.

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+ Field Measurements In The Wake Of A Model Wind Turbine
  Pol, S; Taylor, A; Bilbao, A; Doostalab, A; Novoa, S; Westergaard, C; Hussain, F; Sheng, J; Ren, BB; Giesselmann, M; Glauser, M; Castillo, L
Abstract:  As a first step to study the dynamics of a wind farm, we experimentally explored the flow field behind a single wind turbine of diameter 1.17 m at a hub height of 6.25 m. A 10 m tower upstream of the wind farm characterizes the atmospheric conditions and its influence on the wake evolution. A vertical rake of sonic anemometers is clustered around the hub height on a second tower, 6D downstream of the turbine. We present preliminary observations from a 1-hour block of data recorded in near-neutral atmospheric conditions. The ratio of the standard deviation of power to the inflow velocity is greater than three, revealing adverse effects of inflow turbulence on the power and load fluctuations. Furthermore, the wake defect and Reynolds stress and its gradient are pronounced at 6D. The flux of energy due to Reynolds stresses is similar to that reported in wind tunnel studies. The swirl and mixing produces a constant temperature wake which results in a density jump across the wake interface. Further field measurements will explore the dynamics of a model wind farm, including the effects of atmospheric variability.
+ Frequency Tuning A Reflex Triode Vircator From 1.5 To 5.9 Ghz
  C. F. Lynn; J. Parson; P. Kelly; M. Taylor; D. Barnett; A. Neuber; J. Dickens; J. Mankowski; S. Calico; M. Scott
Abstract:  Vircators (virtual cathode oscillators) are easily frequency tunable by simply altering the electron beam current density through either adjusting the accelerating voltage or varying the anode cathode gap (A-K gap). It is noted that vircators typically exhibit frequency hopping, an often undesired feature. Here we address the frequency hopping problem by introducing a rectangular shaped carbon fiber cathode with the width of the cathode less than one quarter of a wavelength in the direction of microwave propagation. Operating the vircator with the rectangular cathode revealed a match with a resonant condition from back wall reflections, which explains the observed dominant microwave frequency selection. That is, the vircator emitted stably during 50 ns operation at 3.89 GHz or 2.07 GHz with a 3 dB bandwidth of 37.5 MHz or 93.7 MHz, at A-K gap spacing of 8 mm, and 12 mm respectively. To further investigate frequency tuning, the A-K gap was swept from 3 mm to 17 mm while keeping a constant 5.1 cm diameter circular cathode. The resulting frequencies of operation were 1.5 GHz, 2.1 GHz, 4.1 GHz, 4.6 GHz, and 5.9 GHz at A-K gap spacing of 17mm, 14 mm, 7 mm, 5.75 mm, and 3 mm respectively. This demonstrates that a tuning range of 4.4 GHz should be achievable for a practical vircator system.

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+ Large Chip Area Sic Pin Diodes Demonstrated For Thyristor Protection In A Pulsed System
  H. K. O'Brien; W. Shaheen; A. Ogunniyi; C. Scozzie; L. Cheng; M. Hinojosa; K. Lawson; S. Lacouture; S. Bayne
Abstract:  Asymmetric thyristors require protection from voltage and current reversals in high-inductance capacitor discharge systems. Silicon carbide (SiC) PiN diodes capable of blocking up to 16 kV were demonstrated to have the high-current capability to transmit forward pulse current in a series configuration with a thyristor, and to clamp reverse current in an anti-parallel configuration. In series with a thyristor, diodes were switched 1000 pulses at a single-shot rate at 2000 A peak current (3.8 kA/cm2 over anode area and 2100 A2s per pulse) without any notable increases in forward voltage or reverse leakage current. In the reverse clamp configuration, a parallel pair of PiN diodes was demonstrated to block 12 kV charge on the capacitor bank, then clamp a total of 4200 A current reversal with good parallel current sharing. These evaluations demonstrate that for high current density pulsing above 10 kV, individual 16 kV PiN diodes yield lower on-state voltage loss (16 V at 2000 A) than series-stacked assemblies of 9 kV SiC PiN diodes or 6 kV Si diodes.

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+ Measurement And Simulation Of Pulsed Plasma Development At Medium Pressure In A Non-Uniform Field
  A. Fierro; J. Dickens; A. Neuber
Abstract:  The development of plasma in a medium pressure (50 torr) environment in nitrogen was studied by simulation and measurement under the influence of non-uniform, pulsed electric fields. A GPU-accelerated, 3-dimensional particle-in-cell (PIC)/Monte Carlo Collision (MCC) simulation code was written utilizing the CUDA platform to simulate pulsed plasma development in a nitrogen environment and uncover the transient plasma characteristics in detail. The simulation provides significant speed-up over the CPU equivalent implementations. Experimentally, a needle-protrusion (1.5 mm in length, 200 μm tip radius) opposite a brass ground plane with the distance between needle-tip and wall held at 1.5 mm provided a non-homogeneous field. Excitation of the needle-plane gap was achieved with a ~100 ns rise-time high-voltage pulser with a peak voltage of 30 kV. Diagnostics included time-resolved nanosecond gated imaging for light intensity measurements and high speed electrical probes for timing. A time series of the plasma formation captured with a 5 ns camera gate revealed a mostly uniform expanding plasma cloud from the needle tip.

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+ Modular Marx Generator For Dv/Dt Testing Of Power Semiconductor Devices
  W. B. Ray; J. A. Schrock; K. Lawson; S. B. Bayne
Abstract:  A solid-state modular Marx Generator was designed for the purpose of testing the dV/dt capability of Power Semiconductor devices. The Marx Generator is capable of producing up to 1 kV voltage transients with rise times on the order of 10-nanoseconds. This capability to do variable voltage amplitude leads to customizable dV/dt tests. The solid-state modular design will be covered in detail within the paper. The solid-state construction allows for this adjustable dV/dt rating through the utilization of multiple modular stages of Power MOSFETs. These Power MOSFETs have a lower voltage blocking ability, but faster switch closing times. The different modules are controlled through the use of fiber-optic links. These links signal the floating Gate Driver circuitry to synchronize their switch closing time. The floating Gate Driver utilizes isolated switch-mode DC-DC converters to supply the power needed to charge the MOSFET gates, from one ground-referenced power source. The Marx Generator uses high voltage Silicon Carbide Schottky Diodes for the voltage blocking elements when the individual modular stages trigger. The lack of reverse recovery for these high voltage SiC Diodes enables the fast voltage transients that are requisite for dV/dt ranges needed to test Power Semiconductor devices.

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+ Operation Of A 500 Kv, 4 Ka Marx Generator At 500 Hz Rep-Rate
  Taylor, MB; Kelly, PM; Parson, JM; Lynn, C; Dickens, JC; Neuber, AA; Mankowski, JJ; Bragg, JWB; Calico, S; Scott, M
Abstract:  A 42 J, 10-stage pulse forming network (PFN) Marx generator capable of producing a 500 kV, 50 ns full-width-half-max (FWHM), similar to 5 ns rise time pulse into an open load at a rep-rate of 500 Hz has been designed for use as a pulsed power source for a reflex triode virtual cathode oscillator (vircator). Rayleigh PFNs are used in place of discrete capacitors for each stage of the 10-stage Marx generator. Effort was taken to minimize parasitic inductance such that the quality of the pulse shape is maintained as much as possible. In order to rep-rate the Marx generator, a trigatron-based triggering scheme is used to initiate erection of the Marx generator. A 20 ns risetime, 24 kV solid-state pulse trigger generator capable of operating at high repetition rates is used to drive the trigatron. The required charge rate for a 500 Hz pulse repetition frequency (PRF) for the Marx generator is 24 kW. Repetitive operation requires additional design considerations that would be irrelevant to single pulse firing. Pressurized air is jetted across the spark gaps by means of built-in gas manifolds to remove remaining ionized gas between each pulse and prevent premature erection during the subsequent charging cycle. The built-in gas manifolds were designed using a hydrodynamic simulation to ensure equal flow rate across each of the spark gaps and equal pressure along the length of the tube chamber.
+ Overview Of High Voltage 4H-Sic Photoconductive Semiconductor Switch Efforts At Texas Tech University
  D. Mauch; C. White; D. Thomas; A. Neuber; J. Dickens
Abstract:  Recent advances and the current state-of-the-art for high speed 4H-SiC photoconductive semiconductor switches (PCSS) developed at Texas Tech University are summarized. A performance comparison of multiple generations of switch designs is also presented. These devices have experimentally demonstrated the capability of blocking DC electric fields up to 705 kV/cm (<;0.1 mA leakage current), rise times of 0.63 ns (20/80), and switching 20 kV at 250 A with a di/dt of 75 kA/us at a burst repetition frequency of 65 MHz. Findings and optimizations pertaining to device geometry, sub-contact doping, contact thickness, triggering wavelength, and electron irradiation are presented. Device modeling and experimental results investigating current issues with device lifetime are presented as well.

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+ Performance Of St707 Getter Material In A Rep-Rated High Power Microwave Sealed-Tube Vircator Under Uhv Conditions
  Kelly, PM; Parson, JM; Lynn, C; Taylor, M; Dickens, JC; Neuber, A; Mankowski, J; Calico, S; Scott, M
Abstract:  This study focuses on the use of St707 non-evaporable getter (NEG) material in a high power microwave (HPM) sealed-tube virtual cathode oscillator (vircator) operated at repetition rates up to 200 Hz. High-current pulsed operation releases gases trapped within the bulk materials and gas monolayers on material surfaces, leading to localized plasma production between the A-K gap. This potentially leads to gap closure, shortens the duration of microwave production, and spoils low vacuum levels. A single current pulse may increase the chamber pressure to the low 10(-6) Torr range from an initial background pressure in the low 10(-9) Torr range, desorbing approximately 10(14) particles. For single pulse operation, it is sufficient to maintain this background pressure (10(-9) Torr) with a small ion pump rated at 20 L/s. However, at 200 Hz operation, a pumping speed of 1,000 L/s is needed to evacuate 10(14) particles from the vircator volume between pulses. Rather than adding a bulky pump system with the required high pump speed, St707 getter material (70% Zr, 24.6% V, 5.4% Fe) has been used to maintain ultra-high vacuum (UHV) conditions during rep-rate operation. Characteristics of the St707 NEG pump in a repetitive, high-current pulse environment are presented. Diagnostic results obtained with an inverted magnetron cold cathode gauge for absolute pressure are utilized to analyze NEG performance in detail.
+ Pmqc: A Privacy-Preserving Multi-Quality Charging Scheme In V2G Network
  He, M; Zhang, K; Shen, XM
Abstract:  Multi-quality charging, which provides the electric vehicles (EVs) with multiple levels of charging services, including quality-guaranteed service (QGS) and best effort service (BES), can guarantee the charging service quality for the qualified EVs in vehicle-to-grid (V2G) network. To perform the multi-quality charging, the evaluation on the EV's attributes is necessary to determine which level of charging service can be offered to this EV. However, the EV owner's privacy such as real identity, lifestyle, location, and sensitive information in the attributes may be disclosed during the evaluation and authentication. In this paper, we propose a privacy-preserving multi-quality charging (PMQC) scheme in V2G network to evaluate the EV's attributes, authenticate its service eligibility and generate its bill without revealing the EV's private information. Specifically, we propose an evaluation mechanism on the EV's attributes to determine its charging service quality. With attribute based encryption, PMQC can prevent the EV's attributes from being disclosed to other entities during the evaluation. In addition, PMQC can authenticate the EV without revealing its real identity. Security analysis demonstrates that the EV's privacy mentioned above can be preserved by PMQC. Performance evaluation results show that PMQC can achieve higher efficiency in authentication compared with other schemes in terms of computation overhead.
+ Radiation From Sic Pcss Driven Gyromagnetic Nonlinear Transmission Line High Power Microwave Source
  D. V. Reale; D. Mauch; J. M. Johnson; A. A. Neuber; J. C. Dickens; J. J. Mankowski
Abstract:  An all solid-state high power microwave (HPM) source is constructed using a photoconductive semiconductor switch (PCSS) based HV pulse generator to drive a sulfur hexaflouride (SF6) insulated coaxial ferrimagnetic nonlinear transmission line (NLTL) which feeds a TEM horn antenna. The PCSS was fabricated from high purity semi-insulating (HPSI) 4H-SiC and is illuminated with 2 mJ from a frequency tripled Nd:YAG laser at 355 nm with a 7 ns FWHM. Fixed fiber optic delay lines are utilized to generate a burst of four optical pulses from a single solid-state laser source for rep-rate operation. The input to the NLTL is an adjustable pulse from 3 kV to 6 kV with sub-ns rise time and the resulting output of the NLTL is radiation in the L-band to S-band regime with RF power from 100"“200 kW depending on charge voltage. A Rexolite® insulated zipper transition, in which the inner conductor of the coax is gradually exposed, is used at the output of the NLTL to transition from a coaxial structure to parallel plate structure in order to feed a free space TEM horn. The zipper transition and feed section of the TEM horn are potted using Sylgard® 184 silicone elastomer to prevent breakdown at the antenna feed and maintain a homogenous dielectric constant for the transition region. Radiated waveforms are presented for several charge voltages and bias conditions.

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+ Reduction Of High Power Microwave Breakdown Delay Times Using Multiple Passes Through A Te111 Resonator
  S. Beeson; J. Dickens; A. Neuber; S. Lin
Abstract:  Summary form only given. The delay time between the rising edge of a high power microwave (HPM) pulse and plasma formation in a gas at close to atmospheric pressure is studied for a multi-pass geometry. A fundamental lower limit of the breakdown delay time is the formative delay time, defined as the time it takes for the exponentially rising electron density to reach the critical electron density for which the EM wave begins to reflect and attenuate; which is on the order of 10's to 100's of nanoseconds for the conditions of interest. The goal of this research was to surpass this limit by making two passes through the generated plasma with the HPM pulse. That is, an external structure is utilized to time delay the HPM pulse on itself for a second pass through a gas cell.

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+ Rep-Rate Operation Of A ~200 Kv Sealed-Tube Reflex-Triode Vircator At ~200 A/Cm2
  J. M. Parson; J. -W. B. Bragg; M. Taylor; D. Barnett; P. Kelly; C. F. Lynn; S. Holt; J. C. Dickens; A. A. Neuber; J. J. Mankowski
Abstract:  Thermal limitations of anode and cathode materials have shown to negatively impact operation of cold-cathode high-power microwave (HPM) sources. High pulse-repetition-frequency (PRF) operation of these devices exacerbates the problems already experienced in single shot mode where cold-cathode devices, specifically carbon fiber cathodes, are plagued by plasma formation on the anode and cathode followed by plasma/gas expansion that causes impedance collapse of the anode-cathode (A-K) gap. Hence, for frequency stable, repetitive operation, cold-cathode HPM devices require the use of thermally robust electrode materials and ultra-clean surfaces, leading to repeatable tube operation. This study focuses on burst-mode operation of an HPM sealed tube reflex-triode virtual-cathode-oscillator (vircator) for PRFs greater than 100 Hz. The vircator is driven by a 54 J, ~200 kV Marx generator with an approximate pulse width of 50 ns FWHM, and the vircator chamber has an empty volume of approximately 5 L with background pressures in the low 10-9 Torr. The anode materials studied include grade-1 titanium (TiG1), nickel 201L (Ni201L), and stainless steel 316L (SS316L); all in combination with a carbon fiber cathode. Empirically observed outgassing characteristics in conjunction with anode thermal modeling are presented under single-shot and rep-rate conditions. In addition, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) techniques were employed to investigate anode and cathode surface integrities before and after vircator operation.

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+ Rep-Rate Operation Of A 300 Kv, High-Power Microwave Sealed-Tube Vircator
  J. M. Parson; C. F. Lynn; J. -W. B. Bragg; P. Kelly; M. Taylor; D. Barnett; S. Holt; J. C. Dickens; A. A. Neuber; J. J. Mankowski; M. C. Scott; S. E. Calico
Abstract:  Thermal limitations of anode materials are known to impose limits on rep-rate operation of cold-cathode high-power microwave (HPM) sources. This study focuses on performance of pyrolytic graphite (PG) anodes at a 500 Hz burst-mode operation in a reflex-triode virtual-cathode-oscillator (vircator). In most experiments, a 42 J, 300 kV pulse forming network (PFN) based Marx generator with an approximate pulse width of 50 ns full-width-half-max (FWHM), was utilized to drive the vircator. Rep-rated operation of the vircator exacerbates the problems already experienced in single-pulsed mode where vircators are plagued by plasma formation on the anode and cathode followed by plasma/gas expansion that causes degradation of anode materials. Hence, for frequency-stable, repetitive operation, vircators require the use of thermally robust electrode materials and ultra-clean vacuum surfaces, leading to repeatable diode operation. This contribution presents thermal modeling of anode heating and experimental electrical behavior of vircator rep-rate operation.

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+ Ruggedness Evaluation Of 56Mm(2), 180 A Sic Dmosfets As A Function Of Pulse Repetition Rate For High Power Applications
  Lawson, K; Schrock, J; Ray, W; Bayne, S; Cheng, L; Palmour, J; Allen, S
Abstract:  Modern power electronics systems try to maximize power density and efficiency. As such, the active switch is required to safely handle very stressful transient conditions. A 56 mm(2), 180 A, SiC DMOSFET manufactured by Cree Inc. is evaluated by electrically stressing the device in a RLC ringdown test system capable of producing peak current in excess of 600 A (> 3X rated current) and di/dt's as high as 860 A/mu s. The device was hard-switched 5,000 times at repetition rates of 1, 2, 5, and 10 Hz for a total of 20,000 switching events. The device characteristics were monitored every 1,000 shots on a high power curve tracer to determine device degradation. The devices showed no changes in blocking characteristics and minimal changes in on-state characteristics due to shifts in the threshold voltage after 20,000 hard switching events. The threshold voltage shifts over the test period are minimal with a +/- 93 mV deviation from the average of 4.39 V. With the stability of the threshold voltage, on-state characteristics, and blocking characteristics; this shows that this device would perform reliably within commercial applications that include stressful switching conditions.
+ Smart Watch Rssi Localization And Refinement For Behavioral Classification Using Laser-Slam For Mapping And Fingerprinting
  J. D. Carlson; M. Mittek; S. A. Parkison; P. Sathler; D. Bayne; E. T. Psota; L. C. Pérez; S. J. Bonasera
Abstract:  As a first step toward building a smart home behavioral monitoring system capable of classifying a wide variety of human behavior, a wireless sensor network (WSN) system is presented for RSSI localization. The low-cost, non-intrusive system uses a smart watch worn by the user to broadcast data to the WSN, where the strength of the radio signal is evaluated at each WSN node to localize the user. A method is presented that uses simultaneous localization and mapping (SLAM) for system calibration, providing automated fingerprinting associating the radio signal strength patterns to the user's location within the living space. To improve the accuracy of localization, a novel refinement technique is introduced that takes into account typical movement patterns of people within their homes. Experimental results demonstrate that the system is capable of providing accurate localization results in a typical living space.

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+ Stochastic Optimization Based Economic Dispatch And Interruptible Load Management With Distributional Forecast Of Wind Farm Generation
  Yang, L; He, M; Vittal, V; Zhang, JS
Abstract:  We study stochastic optimization of economic dispatch (ED) and interruptible load management using short-term distributional forecast of wind farm generation. Specifically, we develop a Markov-chain-based distributional forecast model for wind farm generation based on spatial and temporal characteristics of the wind turbine power output in a wind farm. Built on the distributional forecast model, the joint optimization of ED and interruptible load management is cast as a stochastic optimization problem. The proposed stochastic ED problem is compared with the deterministic ED problem using the persistence wind generation forecast model, and also with the scenario-based ED formulation which uses all possible wind generation states. Numerical studies, using a modified IEEE RTS 24-bus system and realistic wind measurement data from an actual wind farm, demonstrate the significant benefits obtained by leveraging the Markov-chain-based distributional forecast and the interruptible load management.
+ Thermal Analysis Of 4H-Sic Dmosfet Structure Under Resistive Switching
  B. N. Pushpakaran; S. B. Bayne; A. A. Ogunniyi
Abstract:  This research investigates the electro-thermal switching characteristics and lattice temperature profile of a two dimensional (2D) silicon carbide (4H-SiC polytype) Metal Oxide Semiconductor Field Effect Transistor (MOSFET) cell under resistive switching using Silvaco ATLAS Technology Computer Aided Design (TCAD) physics based simulation software. Physics based models were included to account for recombination effects, bandgap narrowing, low field and high field mobility and lattice heating. The electro-thermal simulation was performed at an ambient lattice temperature of 300K. The device was simulated for 100 A/cm2 and 1000 A/cm2 drain current densities using a 1 kHz 50% duty cycle gate signal consisting of two cycles and 1.6 kHz 80% duty cycle signal consisting of three cycles. The analysis of lattice temperature profile revealed the formation of thermal hot spots in the vicinity of the (Junction Field Effect Transistor) JFET region in the DMOSFET structure during the switching phase and at the edge of the channel during the conduction phase. The magnitude of temperature rise was dependent on the drain current density used during the simulation.

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+ University-Industry Partnership In Semiconductor Engineering
  Dallas, T; Karp, T; Nutter, BS; Lie, YCD; Gale, RO; Cox, R; Bayne, SB
Abstract:  We describe a long-standing and successful university-industry partnership in semiconductor device engineering with a primary focus on product and test engineering. The partnership, now (2013) in its 15(th) year, relies on a symbiotic relationship that has evolved over the years to reflect semiconductor industry trends and advancing university capabilities. The success of the partnership is due to a multifaceted approach with an emphasis on frequent interactions between company personnel and university faculty and students. These interactions feed the core component of the program, student internships. These internships, for which students can obtain course credit, are done at both the undergraduate and graduate level and provide a nearly seamless pathway from school to full-time employment.
Publication Year:  2013
+ 100 Kv High Frequency Transformer/Rectifier Package With Bipolar Voltage Output
  M. Giesselmann; T. Vollmer; W. Carey
Abstract:  A 100kV high frequency transformer / rectifier package was designed and tested which is capable of dual polarity operation. The primary of the transformer is driven by an H-Bridge at a frequency of 20 kHz. The transformer has two HV-coax output cables with a grounded shield on each cable. One of the HV output cables is designated as the positive output terminal whereas the other output cable is designated as the negative output terminal. The shields of both output cables are always grounded. In addition, the core of the transformer is grounded. To obtain either positive or negative output voltage, either of the HV center conductors of the output coax cables is grounded. If the center conductor of the coax cable designated as negative output is grounded, positive voltage is obtained from the coax cable designated as positive output is obtained and vice versa.

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+ A High-Power Transient Coaxial Power Combiner For Nonlinear Transmission Lines
  D. Reale; J. -. B. Bragg; N. Gonsalves; W. Sullivan; A. Neuber; S. Holt; J. Mankowski; J. Dickens
Abstract:  Summary form only given. Recent work on Coaxial Ferrimagnetic Nonlinear Transmissions Lines (NLTL) has been focused on developing an array of NLTLs for use as a solid-state High Power Microwave (HPM) source. The pulsed output of an NLTL requires a combiner that enables combining transient signals at voltage levels up to 50 kV. Existing combiner designs found in literature require resonant structures to achieve efficient power combination, an approach that fails for the short pulse transient signals generated by the NLTL. The novel coaxial combiner is an in-plane structure designed to combine two 50 Ω NLTLs into a single 25 Ω coaxial output which then uses a linear taper to transition back to 50 Ω. The combiner design was simulated using a transient Finite Element Method (FEM) model in COMSOL Multiphysics® and experimental results are compared with simulation. A four-way radial combiner based on the in-plane two-way design is simulated and the field stresses are examined to determine possible operational voltage levels for the four-way design.

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+ Bias Field Controlled Phasing Of Ferrimagnetic Coaxial Nonlinear Transmission Lines
  D. Reale; J. -. B. Bragg; S. Holt; A. Neuber; J. Mankowski; J. Dickens
Abstract:  Coaxial Ferrimagnetic Nonlinear Transmission Lines (NLTL) are utilized as all solid state High Power Microwave (HPM) sources with virtually fixed phase relationship between input voltage pulse and output rf wave. Since the output power of a single NLTL at a given frequency, and of a given size, is limited by the effect of line dimensions as well as charge voltage on operating frequency, we employ an NLTL array to achieve higher power levels. To operate in microwave generation mode the ferrite domains are aligned along the axial direction of the NLTL using a biasing magnetic field generated by a dc current driven solenoid. This biasing method also provides a means of controlling the line delay by adjusting the magnetization of the ferrites using an auxiliary delay coil. By utilizing the delay coil and the primary biasing coil together on an NLTL, the operating frequency can be locked at a given frequency while the delay of the line can be independently adjusted. The relationship between the delay coil field and the corresponding temporal delay is investigated, and two NLTLs fed by identical voltage pulse shapes are combined using the phase control method described.

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+ Current Capabilities Of A Low Inductance Marx Generator For Driving A High Power Microwave Source
  P. Kelly; C. Lynn; J. Parson; M. Taylor; J. Mankowski; A. Neuber; J. Dickens
Abstract:  The electrical characteristics and current capabilities of a low inductance Marx generator used to drive a high power microwave (HPM) source are described. The operating frequency of many HPM sources is dependent upon various characteristics of the input voltage pulse from the pulsed power generator. Texas Tech University has developed an 8 stage, 80 J Marx generator used to drive HPM sources at repetition rates up to 500 Hz. The Marx generator is constructed using pulse forming networks rather than discrete capacitors. Experimental efforts have shown stable frequency operation of a virtual cathode oscillator (Vircator) source using a low energy, PFN Marx. Efforts were taken to reduce parasitic inductance of the PFN Marx resulting in a voltage pulse with a risetime less than 25ns with 50ns FWHM. Additionally, efforts were taken to improve impedance matching between the PFN Marx and the vircator load. This article presents experimental results of an 80 J Marx at voltages ranging from 150 kV to 250 kV operating in burst mode. Voltage and current waveforms from the Marx are shown as well as some typical results of compact sealed tube vircator operation.

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+ Design Of An Advanced Modular Automated Evaluation System For Experimental High Power Sgtos
  S. Lacouture; K. Lawson; S. Bayne; M. Giesselmann; H. O'Brien; A. Ogunniyi; C. J. Scozzie
Abstract:  An advanced evaluation system for experimental high power Super Gate Turn Off Thyristors (SGTOs) with built - in custom data acquisition and characterization electronics was designed and built in a cooperative agreement between engineers at Texas Tech University's Center for Pulsed Power and Power electronics (P3 E) laboratory and research scientists at Army Research Lab (ARL). The system consist of a Pulse Forming Network (PFN) energized by a rapid capacitor charger, a data acquisition system which records chosen waveforms for each test cycle and a curve tracing module which the test devices are mechanically switched into to record current and voltage characteristics at arbitrary intervals between high power cycles. Testing is completely automated, with all test parameters including charge level, repetition rate, volume, etc. set within a windows based GUI. The evaluation system has successfully recorded changing I - V characteristics before actual physical failure in several devices. Extremely high volume testing has also been carried out with one device having been cycled over 42,000 times at moderate (2.5 kA) conduction levels.

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+ Design Of An Advanced Modular Automated Evaluation System For Experimental High Power Si And Sic Sgtos
  K. Lawson; S. Lacouture; S. Bayne; M. Giesselmann; H. O'Brien; A. Ogunniyi; C. J. Scozzie
Abstract:  An advanced evaluation system for experimental high power silicon (Si) and silicon carbide (SiC) Super Gate Turn Off Thyristors (SGTOs) with custom data acquisition and characterization electronics was designed and built in a cooperative agreement between engineers at Texas Tech University's (TTU) Center for Pulsed Power and Power Electronics (P3E) laboratory and research scientists at the U.S. Army Research Lab (ARL). The system consists of a 4.4 kJ Pulse Forming Network (PFN) energized by a 10 kW rapid capacitor charger developed at TTU, a data acquisition system which records chosen waveforms for each test cycle and a curve tracing module which the test devices are mechanically switched into to record current and voltage characteristics at arbitrary intervals between high power cycles. Testing is completely automated, with all test parameters including charge level, repetition rate, volume, etc. set within a custom windows based GUI. The evaluation system has successfully recorded changing I-V characteristics before actual physical failure in several devices. Extremely high volume testing has also been carried out with one device having been cycled over 30,000 times at moderate (2.5 kA) conduction levels. This paper expands on work presented at the 2012 Power Modulator Conference and presents newly acquired data and modifications.

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+ Electro-Thermal Transient Simulation Of Silicon Carbide Power Mosfet
  B. N. Pushpakaran; S. B. Bayne; A. A. Ogunniyi
Abstract:  This research illustrates the transient performance of N-channel silicon carbide (4H-SiC) power MOSFET rated for a blocking voltage of 1200V and drain current density of 100A/cm2. The simulation of vertical D-MOSFET half cell structure was performed at room temperature of 300K. The 2D device model was created and simulated using Silvaco© ATLAS Technology Computer-Aided Design (TCAD) physics based simulation software. Physics based models were used to accurately model electrical device parameters including carrier mobility, recombination effects, bandgap narrowing, impact ionization and lattice heating.

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+ Frequency Tunable Sealed Tube Reflex Triode Vircator
  M. Taylor; P. Kelly; C. Lynn; J. Parson; J. Mankowski; A. Neuber; J. Dickens; M. Kristiansen
Abstract:  Summary form only given. A virtual cathode oscillator (vircator) is a high power microwave device that exhibits frequency tunability which is inherent to its principle of operation. Two types of electron motion within the vircator generate microwaves (virtual cathode oscillation and reflexing electron motion). Although it is difficult to precisely predict the dominant microwave frequency of a vircator design prior to experimental observation, the oscillation frequency of the virtual cathode is approximately proportional to the plasma frequency of the electron beam as it enters the virtual cathode. Additionally, the reflexing electrons oscillate at a frequency which is inversely proportional to approximately four times the transit time of an electron through the anode-cathode gap (A-K gap). As a result, assuming space charge limited diode operation, the virtual cathode and reflexing electron oscillation frequencies, though different, are proportional to V1/2/d, where d is the gap separation of the A-K gap and V is the accelerating voltage applied to the gap. Thus vircators are tunable via adjusting the A-K gap and varying the applied accelerating voltage. Texas Tech University has developed a sealed tube vircator which radiates approximately 100 MW with an operational frequency of 4GHz. Operating at 4GHz the diode has an A-K gap of 8mm, an accelerating voltage of ~200 k V, and electron beam current of ~3.5kA. Here we present an experimental investigation of the tunability of a reflex triode vircator by varying the A-K gap from 4 mm to 10 mm and accelerating voltages ranging from 150 kV to 250 kV.

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+ High Performance, Large-Area, 1600 V / 150 A, 4H-Sic Dmosfet For Robust High-Power And High-Temperature Applications
  L. Cheng; A. K. Agarwal; M. Schupbach; D. A. Gajewski; D. J. Lichtenwalner; V. Pala; S. -H. Ryu; J. Richmond; J. W. Palmour; W. Ray; J. Schrock; A. Bilbao; S. Bayne; A. Lelis; C. Scozzie
Abstract:  In this paper, we report our recently developed 2nd Generation, large-area (56 mm2 with an active conducting area of 40 mm2) 4H-SiC DMOSFET, which can reliably block 1600 V with very low leakage current under a gate-bias (VG) of 0 V at temperatures up to 200°C. The device also exhibits a low on-resistance (RON) of 12.4 mΩ at 150 A and VG of 20 V. DC and dynamic switching characteristics of the SiC DMOSFET have also been compared with a commercially available 1200 V/ 200 A rated Si trench gate IGBT. The switching energy of the SiC DMOSFET at 600 V input voltage bus is > 4X lower than that of the Si IGBT at room-temperature and > 7X lower at 150°C. A comprehensive study on intrinsic reliability of this 2nd generation SiC MOSFET has been performed to build consumer confidence and to achieve broad market adoption of this disruptive power switch technology.

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+ High Voltage Solid Dielectric Coaxial Ferrimagnetic Nonlinear Transmission Line
  D. Reale; J. -. B. Bragg; R. Solarski; A. Neuber; S. Holt; J. Mankowski; J. Dickens
Abstract:  Previously developed coaxial ferromagnetic Nonlinear Transmission Lines (NLTL) relied solely on pressurized Sulfur Hexaflouride (SF6) as high-voltage insulating dielectric medium [1]. While the use of SF6 provides the necessary electric insulation, there are drawbacks including gas storage and pressure fittings that increase system size and add to the design complexity of the NLTLs themselves. We evaluate solid dielectric materials as an alternative. Initial attempts used a standard high voltage (HV) epoxy to pot the NLTL assembly. This method was effective at producing magnetic precession in the NLTL; however, there was a reduction in output power due to the high loss tangent of the epoxy. Sylgard 184, commonly used in solar cells, has been widely used as an HV potting material and has an order of magnitude lower loss tangent than standard HV epoxy at 1 kHz. Samples of HV epoxy and Sylgard 184 are tested in a microwave cavity resonator at 3 GHz to determine their loss tangents. The performance of an NLTL potted with Sylgard 184 is compared to that of the HV epoxy NLTL and the current SF6 insulated NLTL.

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+ Microwave Radiation From A Sic Pcss Driven Gyromagnetic Nltl
  J. -. B. Bragg; W. W. Sullivan; D. V. Reale; D. L. Mauch; S. Holt; A. A. Neuber; J. Mankowski; J. C. Dickens
Abstract:  An all solid-state high power microwave system comprised of a photoconductive semiconductor switch (PCSS) and nonlinear transmission line (NLTL) is presented. A single 50 kV 4H-Silicon Carbide (SiC) PCSS switches 7 ns (FWHM) pulses with 2 ns risetime into the gyromagnetic NLTL. The PCSS achieves sub-ohm resistance when illuminated by approximately 3 mJ of laser energy emitted from a tripled Nd:YAG laser (355 nm). Utilizing a fiber optic based optical triggering system enabled generating a train of laser pulses, and burst-mode operation with 65 MHz pulse repetition frequency was achieved. The NLTL sharpens the fast rising pulse from the PCSS and produces MW-class rf power levels at 2-4 GHz. Microwave generation is achieved through stimulation of damped gyromagnetic precession when the static and pulsed external magnetic fields interact with the magnetic moments of the nonlinear ferromagnetic material. The acting nonlinear material is a NiZn composite with dimensions 3 mm × 6 mm (ID × OD). The system is terminated with a wideband antenna consisting of a coaxial to parallel-plate conversion balun which is then immediately flared to provide a linearly-flared TEM horn antenna. The entire length of the compact HPM system measures 1.15 m. Radiation results for single shot and burst-mode operation are presented as well as demonstration of operational frequency control.

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+ Multiple Cell Ac/Dc Smart Battery Design
  T. J. Rosson; S. Bayne; R. Gale
Abstract:  Traditional multi-cell battery packs use a fixed configuration to connect multiple individual battery cells in fixed configurations to achieve pre-determined voltage and current. Even with modern advances in battery chemistry and greater power density, this fixed configuration results in low reliability, low fault tolerance, and non-optimal energy conversion efficiency. This system of manufacture is hindering advances in battery performance. This paper proposes a novel scheme to manufacture batteries by individualizing cells. By changing the packaging and adding low cost circuitry, a single cell in a battery pack will be able to control its orientation with other cells in a system. The idea has potential to revolutionize the way in which battery systems are developed and controlled. By using Texas Instruments value line MSP430 microcontrollers, the cost of the system can be minimized. The use of these low cost microcontrollers makes it possible to monitor voltage and temperature levels on individual cells. Also, by utilizing the same microcontroller, the individual cell is capable of shifting individual battery cells from off state, to a positive or negative polarity. The ability to switch single cells will make it possible to create a multi-level DC output. This independent switching scheme will also make it possible to create a modified sine wave AC output. The possibilities of switching to negative polarity will double the peak-to-peak voltage of the AC waveform. The battery will also be capable of identifying and implementing only the cells that are in optimal condition. Using cells at optimal temperature and state of charge will prolong the life of each cell. A battery system that individualizes each cell into a replaceable package makes replacement of "dead cells" possible. These are the cells that currently cause traditional battery packs to be replaced. With such systems available, not only will efficiency of large multi-cell battery systems increase, but with replaceable cells the cost of ownership of a complete battery pack will decrease over the lifetime of the system.

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+ Performance And Characterization Of A 20 Kv, Contact Face Illuminated, Silicon Carbide Photoconductive Semiconductor Switch For Pulsed Power Applications
  D. L. Mauch; W. W. Sullivan; A. B. Bullick; A. A. Neuber; J. C. Dickens
Abstract:  A 20 kV, lateral geometry, contact face illuminated, silicon carbide (SiC) photoconductive semiconductor switch (PCSS) is presented. The SiC PCSS was fabricated from high purity semi-insulating, bulk 4H-SiC (12.7 mm × 12.7 mm × 0.35 mm), in a lateral geometry, (0.6 mm gap) with both the anode and cathode contacts located on the same face of the device. The device was illuminated with light from a tripled Nd:YAG laser (355 nm-7 ns FWHM) entering from the contact face. The device demonstrated sub-ohm on-state resistance for laser pulse energies in the mJ range, and micro-amp leakage currents at 20 kVdc in the off-state. Voltage hold-off and low leakage currents in the off state were achieved through high energy electron beam irradiation of the bulk material. The switch's geometry and packaging are discussed, along with experimental switching and blocking characteristics.

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+ Performance Of Neg Getter Materialin A Sealed Reflex-Triode Vircator At 225 A/Cm2
  P. Kelly; J. M. Parson; C. F. Lynn; J. J. Mankowski; J. C. Dickens; A. A. Neuber
Abstract:  Summary form only given. This study focuses on the use of non-evaporable getter (NEG) materials in a high power microwave (HPM) virtual-cathode oscillator (vircator). The vircator has a background pressure in the low 10-9 torr range with a vacuum volume of 5 L backed by a small 20 L/s ion pump. Presently, the source is driven by an 80 J, 300 kV Marx generator with a current density of 225 A/cm2 and pulse width of 100 ns. Initial current pulses increases the chamber pressure to the low 10-6 torr range desorbing approximately 1014 particles1,2. Reduction in the number of particles desorbed decreases an order of magnitude after approximately 2,000 current pulses, with no further noticeable decrease after 10,000 pulses3. The HPM system will eventually be modified to operate at 500 Hz with a pulse width between 10-20 ns. In first order approximations, a pumping speed of 2500 L/s will be needed to pump 1014 particles within 2 ms from a 5 L volume. This corresponds to a surface area of approximately 2400 cm2 for a zirconium-vanadium-iron (ZrVFe) getter material. An introduction of NEG materials into the vacuum chamber will aid in achieving repetitive operation; and preliminary results on the use of the NEG material in the vacuum environment will be presented. A residual gas analyzer (RGA) and an inverted-magnetron cold cathode vacuum sensor are used for the gas diagnostics and are rated to survive the 300°C, 72 hour vircator bake out process.

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+ Post Pulse Recovery Of Hpm Generated Plasma At Close To Atmospheric Pressure
  S. R. Beeson; J. C. Dickens; A. A. Neuber
Abstract:  Summary form only given. We study the recovery of the low temperature plasma generated by a microsecond high power microwave, HPM, pulse in different gases at pressures approaching one atmosphere. The experiment mimics the electrical breakdown at the interface between the vacuum HPM-source environment and the radiating environment (generally held at atmospheric pressure). This low temperature plasma is generated along the surface on the atmospheric side where the high Eeff/p, or reduced effective electric field with pressure, causes high levels of ionization leading to the formation of a highly conductive plasma within the duration of the microsecond pulse. With the maximum HPM pulse repetition rate being highly dependent on the relaxation of this plasma, it is the goal of this study to determine the kinematics and chemistry of this low temperature plasma as it pertains to ion, electron, and excited species densities. For this study, a 2.85 GHz magnetron operating in the TE10 mode of a WR-284 standard waveguide is used to generate a 3 MW, 3 microsecond pulse with a rise time of less than 50 ns that is incident on the dielectric window separating the two environments. The atmospheric side is enclosed in a structure that mimics an open radiation pattern similar to that of current HPM systems. To understand the post-pulse features, two custom multi-standard waveguide couplers were designed to implement and extract a low power 10 GHz CW source into the main waveguide structure while keeping a low insertion loss for the HPM pulse. The results of this power signal (max attenuation values range -10 to -40 dB) along with a 1D plane wave excited plasma model is used to infer the temporal average electron density (specifically the longitudinal integral of the surface plasma density) at a range of pressures and different gases, typically 10-400 torr for air, N2, Ar, and He. The peak electron density and loss rates are then correlated with diffusion lengths, recombination and attachment rates given in literature to ascertain the dominant plasma relaxation path and species along with a means to extrapolate the time required to relax to a nominal background electron density. For instance, the dominant electron loss process in 90 torr air is attachment with a frequency of 121 kHz and peak electron density of ~1013 cm-3 resulting in relaxation times of a few hundred microseconds while in N2, the dominant process soon after the pulse is determined to be 2-body dissociative recombination.

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+ Pulsed Power Switching Of 4H-Sic Vertical D-Mosfet And Device Characterization
  A. Bilbao; W. B. Ray; J. A. Schrock; K. Lawson; S. B. Bayne; L. Cheng; A. K. Agarwal; C. Scozzie
Abstract:  The purpose of this research is to characterize and compare CREE's new N-Channel Silicon Carbide (4H-SiC) vertical power D-MOSFET with CREE's previous generation of N-Channel Silicon Carbide (4H-SiC) vertical power D-MOSFET. Changes made to the newest MOSFET design lead to a 400% increase in pulsed current handling capability over the previous generation device with the same active area.

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+ Rapid Capacitor Charger And Battery System For Portable Pulsed Power Applications
  S. L. Holt; J. C. Dickens; J. J. Mankowski; G. Rodriquez
Abstract:  The design of a scalable, burst-mode rapid capacitor charger and a high power battery system will be discussed. The design is scalable up to 40 kW output power and operates at 50 k V. The system is powered by a Lithium Ion Polymer (LiPo) battery pack and includes a battery management system. The topology is derived from a 5 kV, 3 kJ/s battery power capacitor charger that was previously demonstrated. This smaller charger occupied a volume of 1.5 L including batteries and demonstrated a 2 kW/L average power density over a 1 s burst. This power density is five to ten times higher than commercially available systems. The performance of this previous design was limited by strict form factor restrictions (1.5 L, 6" diameter). The new design is intended to match or exceed the power density of the previous design due to reduced form factor restrictions. Electrical and mechanical design, component selection, and circuit simulations will be presented.

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+ Reliable Operation Of Sic Junction-Field-Effect-Transistor Subjected To Over 2 Million 600-V Hard Switch Stressing Events
  Steiner, B; Bayne, SB; Veliadis, V; Ha, HC; Urciuoli, D; El-Hinnawy, N; Borodulin, P; Scozzie, C
Abstract:  A necessity for the successful commercialization of SiC power devices is their long term reliability under the switching conditions encountered in the field. Normally-ON 1200 V SiC JFETs were stressed in repetitive hard-switching conditions to determine their fault handling capabilities. The switching pulses were generated from an RLC circuit, where energy initially stored in capacitors discharges through the JFET into a resistive load. The hard-switching included one million repetitive pulsed hard-switching events at 25 degrees C from a drain blocking-voltage of 600 V to an on-state current of 67 A, and an additional one million 600-V/63-A pulsed hard-switching events at 150 degrees C. The JFET conduction and blocking-voltage characteristics are virtually unchanged after over two million hard switching events proving the devices are reliable for handling high surge-current faults like those encountered in bidirectional circuit breaker applications.
+ Spatio-Temporal Analysis For Smart Grids With Wind Generation Integration
  He, M; Yang, L; Zhang, JS; Vittal, V
Abstract:  In this paper, we propose a spatio-temporal analysis approach for short-term forecasting of wind farm generation. Specifically, using extensive measurement data from an actual wind farm, the probability distribution and the level crossing rate (LCR) of wind farm generation are characterized by using tools from graphical learning and time-series analysis. Based on these spatial and temporal characterizations, finite state Markov chain models for wind farm generation are developed. Point-forecast of wind farm generation is derived using the Markov chains and integrated into power system economic dispatch. Numerical study on economic dispatch using the IEEE 30-bus test system demonstrates the significant improvement compared with conventional wind-speed-based forecasting methods.
+ Study Of Low-Temperature Plasma Development Utilizing A Gpu-Implemented 3D Pic/Mcc Simulation
  A. S. Fierro; G. R. Laity; S. R. Beeson; J. C. Dickens; A. A. Neuber
Abstract:  Summary form only given. A GPU-accelerated 3-dimensional PIC/MCC simulation code was developed using the CUDA environment to study the physical processes involved in the development of a low-temperature plasma. The simulation results aid in quantifying transient plasma development as it is often inaccessible experimentally in detail even with modern noninvasive techniques such as non-linear laser spectroscopy or high-speed electrical diagnostics. Hence, computational methods, such as Particle-in-Cell (PIC) and Monte Carlo Collision (MCC), provide a complementary approach to determining the mechanisms leading to plasma development. However, fully modeling the physics of the plasma development is made difficult by the number of plasma processes that must be tracked simultaneously, and only recently have computing resources provided the capability to track tens of millions of particle interactions. Furthermore, the introduction of graphics processing unit (GPU) computing provides an attractive means for economical and efficient parallelization of scientific codes through a framework such as NVIDIA CUDA. As such, a GPU-accelerated 3-dimensional PIC/MCC simulation was developed using the CUDA environment to provide characteristics during the initial stage of plasma development in atmospheric pressure nitrogen. The simulation was run on a NVIDIA GTX 580 with 3 GB of memory and 512 CUDA cores. The simulated geometry consists of two paraboloid electrodes with a gap distance of 5 millimeters with Dirichlet boundary conditions, and 22 unique electron interactions with molecular nitrogen are considered. The electrodes are excited with a step voltage pulse of several thousand volts also assuming a uniformly distributed initial electron density of 104 cm-3 in the volume. For instance, results from a 5 nanosecond simulation reveal the development of positive ion space charge channels near the anode and cathode regions. These channels appear consistent with high-speed streamer photographs captured during plasma formation. The electron energy distribution function (EEDF) indicates a non-Maxwellian velocity distribution during the application of the high electric field. Furthermore, a typical electron density near the cathode is on the order of 7 × 108 cm-3. The results from numerical simulation will be compared in detail to experimentally accessible parameters such as electron temperature and dissociation degree.

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+ Study On The Relationships Between Development Of Sports Industry And Economic Environment
  He, M
Abstract:  With the increase of people's income and the improvement of their living standards, the need for sports and fitness, recreation and entertainment is also undergoing substantial increase. It is of great importance to meet these growing needs, which provides a broad market for the sports industry. It is an inevitable trend to develop the sports industry market on a large scale. It has positive effect on sports quality improving, sports level promoting and sports development accelerating so as to promote the development of sports economy. From the perspective of economy environment, this paper describes the necessity of develop sports industry on a scale and problems need to be concerned. From the development perspective, the economic environment analysis and research of sports industry market scale offer managers and relevant decision makers meaningful reference. By using the methods of documentation, questionnaire, interview and investigation, mathematical statistics and logical analysis, the author,in two aspects of theories and demonstration, studied the relationships between development in scale of sports industry and economic environment.
Publication Year:  2012
+ A Heterogeneous Modules Interconnection Architecture For Fpga-Based Partial Dynamic Reconfiguration
  He, M; Cui, YZ; Mahoor, MH; Voyles, RM
Abstract:  This paper proposes and analyzes a novel FPGA-based System-on-Chip (SoC) module interconnection architecture called the Morphing Crossbar, which enables time-efficient partial dynamic reconfiguration of embedded systems built with programmable logic. By combining local Crossbar and its companion peripheral interconnection bus, the Morphing Bus, compact embedded systems can be developed with both static and dynamic reconfigurability. The Morphing Crossbar decreases the overhead of interconnection and remapping by allowing the system components to be modularized into relocatable modules. This method increases the flexibility of dynamic partial reconfigurable system. The Morphing Crossbar, which allows adding, removing, or swapping module blocks inside the system on the fly, was implemented on the Xilinx Virtex-5 architecture. Our experimental results demonstrate that by using Morphing Crossbar, adding, removing, and swapping modules can be performed 3.6 times faster compared to architectures without Morphing Crossbar.
+ A Self-Adaptation Framework For Resource Constrained Miniature Search And Rescue Robots
  Cui, YZ; Voyles, RM; He, M; Jiang, GY; Mahoor, MH
Abstract:  The size of miniature urban search and rescue robots forces constraints on critical resources such as power, space, and computational ability. To alleviate the effect of resource constraints, it is prudent to let robots adapt themselves autonomously in reaction to unforeseen conditions in disaster area. Software adaptation has been the goal of many researchers, but hardware adaptation is an important aspect, too. In this paper, we present a self-adaptation framework for heterogeneous multi-robot collectives, which consists of partial dynamic reconfiguration for hardware adaptation, module migration for software adaptation, and task performance evaluation to enable autonomous adaptation. These things taken together represent an Embedded Virtual Machine for hardware/software task migration. Our Morphing Crossbar structure, which interconnects reusable hardware modules, is presented to increase the partial dynamic reconfiguration performance. Combined with the run-time downloading and installation of reusable software modules based on the port-based object framework in our PBO/RT real-time operating system, high-performance, heterogeneous, run-time adaptation of hardware/software real-time computational systems is achieved. The adaptation evaluators provide the ability of robotic systems to self-diagnose and self-adapt with an appropriate, distributed configuration monitor. We have implemented this self-adaptation framework in our RecoNode CPU node. By using RecoNode-based CRAWLER and HexRotor robots, an application scenario is presented in order to show the feasibility of this framework.
+ A Simulation Of Breakdown Parameters Of High Power Microwave Induced Plasma In Atmospheric Gases
  P. J. Ford; J. Krile; H. Krompholz; A. Neuber
Abstract:  Surface flashover induced by a High Power Microwave fast rise-time pulse causes a significant drop in transmitted power, along with reflections that can damage the source. Momentum transfer collision rates in the range of 100s of GHz (for pressures exceeding 5 kPa) lead to low plasma conductivity, corresponding to absorption levels of up to 60 % of the incident power. A simulation algorithm was developed using the finite-difference time-domain (FDTD) method in order to model the growth and transport of the electron density near a dielectric surface, and the resulting interaction with the microwave pulse. The time-dependent plasma parameters are governed by empirical and simulated scaling laws for ionization and collision rates, along with diffusion coefficients; the resulting frequency-dependent plasma permittivity is transformed to a discrete algorithm to describe the spatially resolved plasma in the FDTD algorithm. A plasma thickness of up to 2 mm is simulated that compares with side-on ICCD imaging of surface flashover. Breakdown parameters, such as delay times and breakdown electric fields, in nitrogen, air and argon, are compared with experimental data on surface flashover across a polycarbonate window at atmospheric pressures; the simulated results correlate well with measured, and the model exhibits low computational complexity when simulating a pulse on the order of microseconds, making it a good alternative to standard particle-in-cell codes. The source is a S-band magnetron that produces a 2.5 MW peak power, 50 ns rise-time pulse with 3 μs duration at 2.85 GHz center frequency.

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+ Alpha Schottky Junction Energy Source
  Litz, MS; Fan, ZY; Carroll, JJ; Bayne, S
Abstract:  Isotope batteries offer solutions for long-lived low-power sensor requirements. Alpha emitting isotopes have energy per decay 103 times that of beta emitters. Alpha particles are absorbed within 20 mu m of most materials reducing shielding mitigation. However, damage to materials from the alphas limits their practical use. A Schottky Barrier Diode (SBD) geometry is considered with an alpha emitting contact-layer on a diamond-like crystal semiconductor region. The radiation tolerance of diamond, the safety of alpha particles, combined with the internal field of the SBD is expected to generate current useful for low-power electronic devices over decades. Device design parameters and calculations of the expected current are described.
+ Analysis And Comparison Between Two Wind Farms Consisting Of 500Kw Midsize Turbines And 1.5Mw Turbines
  S. R. Pappu; S. Nimmagadda; S. B. Bayne
Abstract:  This paper compares the characteristics of two wind farms of same power capacity having two different size generators. The research compares the performance of mid-size turbines to large turbines. The systems were modeled in MATLAB-Simulink. With rapid development in wind power generation it's necessary to study the different characteristics of wind farms having different generator configurations. A 9MW wind farm consisting of eighteen Fixed Speed Induction Generators (FSIG) with STATCOM at the terminals of the wind farm is compared to a 9MW wind farm consisting of six Doubly Fed Induction Generators (DFIG) interfaced with Power Electronics on the rotor. The models of FSIG wind power generation system and DFIG wind power generation system connected to the grid are built. An analysis on total power available for transmission, reactive power consumption at different wind speeds (cut in, rated, cut off), power loss due to loss of turbines.

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+ Anode Material Outgassing At 250 A/Cm2 Current Density Under Uhv Conditions
  J. M. Parson; J. C. Dickens; A. Neuber; J. Walter; M. Kristiansen
Abstract:  Summary form only given. This presentation describes a study on gas evolution of plasma expansion in a reflex-triode virtual cathode oscillator (vircator) at ultra-high vacuum (UHV). Research has shown that explosive electron emission (EEE) processes at the cathode and ion / electron bombardment at the anode cause material erosion that produces regions of localized plasma. This plasma expansion has shown to lower gap impedance, cut off microwave performance and spoil low vacuum levels over time1. The goal of the study is to identify the gas species and their sources to better understand and limit the negative effects of plasma expansion in sealed tubes. The vacuum tube under investigation is a triode-geometry vircator with 20 cm2 cathode surface, driven by a 80 J Marx Generator with an approximate peak voltage and current, and pulse width of 200 kV and 5 kA, and 200 ns, respectively.

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+ Avalanche Breakdown Energy In Silicon Carbide Junction Field Effect Transistors
  Hinojosa, M; Bayne, S; Veliadis, V; Urciuoli, D
Abstract:  The energy dissipation capabilities of a 4H-SiC, 1200 V, 0.1 cm(2) JFET operating in blocking mode were investigated. These devices, which are used in bidirectional solid-state circuit breaker applications, can conduct a current of 13 A in forward-conduction mode, and typically block a voltage up to 1200 V in reverse bias mode. In this document, the blocking limits of the device were pushed slightly to the point where avalanche breakdown occurs. A high voltage, short-pulse generator was designed and constructed to drive the JFET into this state and to monitor the dissipated energy. The devices were able to handle up to 18.14 mJ.
+ Characterization Of Annealed Hpsi 4H-Sic For Photoconductive Semiconductor Switches
  Hettler, C; Sullivan, WW; Dickens, J
Abstract:  Annealing of high purity semi-insulating (HPSI) 4H-SiC is investigated as a method to improve bulk photoconductive semiconductor switches through recombination lifetime modification. Five samples of HPSI 4H-SiC were annealed at 1810 degrees C for lengths of time ranging from 3 to 300 minutes. The recombination lifetime of the unannealed and annealed samples was measured using a contactless microwave photoconductivity decay (MPCD) system. The MPCD system consists of a 35 GHz continuous microwave probe and a tripled Nd:YAG pulsed laser. The recombination lifetime was increased from 6 ns, as received, up to 185 ns by annealing for 300 minutes. To experimentally verify switch improvements, identical switches from unannealed and annealed material were fabricated and tested at low voltage. The unannealed device generated a 15 ns pulse with a 2 ns rise-time. The annealed device conducted for upwards of 300 ns with a comparable 2 ns rise-time. The increased recombination lifetime resulted in lower on-state resistance and increased energy transfer.
+ Comparison Of Csi Coated Carbon Velvet And Aluminum Cathodes Operated At Current Density On The Order Of 300 A/Cm2
  C. Lynn; J. Walter; A. Neuber; J. Dickens; M. Kristiansen
Abstract:  Many high power microwave devices use explosive or flashover electron emission cathodes in order to generate the electron beam and thus drive the device. These diodes are simple to operate, requiring no heater or other external systems, and are capable of generating beam currents of several kA at accelerating voltages on the order of 100s of kV. However, they generally suffer from non-uniform emission, anode heating, out-gassing, and pulse shortening due to anode and cathode plasma expansion. The ability to rep-rate such a diode is generally limited by anode heating and out-gassing which are both affected by beam uniformity. Two diodes are compared in this work. One uses a machined aluminum cathode, which is made from solid aluminum with grooves milled onto the surface. The other diode utilizes a carbon velvet cathode which is CVD coated with CsI. Time integrated scintillator images of the electron beam at the anode were taken for both the carbon velvet and aluminum cathodes. Additionally, time resolved images of the emission centers were taken for the carbon velvet cathodes. Data sets of over 1000 shots were taken with each cathode and shot to shot variation in the peak "turn-on" electric field are compared. The lifetime of the aluminum cathode was exceeded before 1000 shots, whereas the carbon velvet cathode showed no degradation in operation.

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+ Design Of An Automated Test Bed For Experimental Si And Sic Sgto Devices
  K. Lawson; S. Lacouture; S. B. Bayne; M. Giesselmann; T. Vollmer; H. O'Brien; C. Scozzie; A. Ogunniyi
Abstract:  In a collaborative effort between Army Research Lab (ARL) and Texas Tech University's center for Pulsed Power and Power Electronics (P3E) lab, a high power, high energy test bed meant to characterize experimental Si and SiC Super Gate Turn Off (SGTO) devices was designed and built. The system was engineered to run the devices through an arbitrary number of test cycles while recording all pertinent data automatically. Test parameters are set through a windows GUI which communicates with a microprocessor - based control system that orchestrates timing and settings of each subsystem as well as acquiring voltage and current waveforms with high speed ADCs operating simultaneously in parallel. The test waveform itself is generated by a Pulse Forming Network (PFN) which accurately controls rise time, fall time and pulse width. The PFN is charged by a Rapid Capacitor Charger (RCC) system designed at the P3E lab that is capable of 10 kW and allows precise charge voltage levels to be set. Waveforms are acquired through isolated probes specifically designed to capture desired signals even in the presence of a large bias voltages.

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+ Electron Density Evolution Of Post-Pulse High Power Microwave Plasma
  S. Beeson; A. Neuber
Abstract:  Plasma generation along the dielectric interface between the vacuum medium of the source and the atmospheric environment of the antenna is one of the limiting factors in power thresholds of high power microwave, HPM, systems. The maximum repetition rate for HPM platforms are ultimately determined by the relaxation times of this low-temperature surface plasma. While the microwave scattering parameters can be determined during the HPM pulse from the transmitted and reflected pulse itself, additional diagnostics effort has to be expended to capture post-pulse plasma relaxation and microwave scattering parameters. For this, a Bethe hole-type multi-standard waveguide coupler was designed and fabricated to inject a continuous low power signal into the main waveguide structure that carries the main 3 MW, 3 µs pulse at 2.85 GHz in an S-band waveguide structure. To facilitate flashover the waveguide is terminated by a Lexan window into a controlled atmospheric chamber with absorbing walls that mimic radiation into free space. The coupler injects 1W of continuous power at 10 GHz to measure the scattering parameters many microseconds after the pulse extinguishes. Using a model developed from a 1D plane wave excitation, the plasma's electron density can be inferred from these power measurements. Then, from the temporal analysis of the electron density, the kinematic and chemical behavior of the plasma in relation to the recombination and attachment properties of the gas are inferred. Tested conditions include three gas types: N2, air, Ar, ranging in pressure from 10 to 155 torr. The transmission coefficients range from -40 to -10 dB corresponding to an electron density of ~1014 to ~1011 cm-3 for these pressures, respectively. The decay of this plasma has been experimentally determined to be on the order of tens of microseconds with the density falling off proportional to t-1, t-2, exponential, or a linear combination thereof, depending on the dominant electron loss path. Reported here, are the design parameters of the waveguide coupler along with the post-pulse evolution of the electron density and recombination physics that it entails.

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+ Evaluation Of High Power Experimental Sic Sgto Devices For Pulsed Power Applications
  Lacouture, S; Lawson, K; Bayne, S; Giesselmann, M; O'Brien, H; Scozzie, CJ
Abstract:  The development of new semiconductor designs requires that extensive testing be completed in order to fully understand the device's characteristics and performance capabilities. This paper describes the evaluation of experimental Silicon Carbide high power Super Gate Turn Off Thyristors (SiC SGTOs) in a unique test bed that is capable of stressing the devices with very high energy/power levels while at the same time mimicking a realistic, real world application for such devices.
+ Evaluation Of Hub Concept For Wind Turbines
  S. R. Pappu; S. B. Bayne
Abstract:  This paper simulates the transient response of three wind farms interconnected, rated 9MW each. Each wind farm consists of six Doubly Fed Induction Generator (DFIG) turbines rated at 1.5MW each, interfaced with power electronics on the rotor side. The three wind farms connected to the grid are built and modelled in MATLAB-Simulink. With the rapid development in Generation Interconnect Requests and development of the Hub concept, it is necessary to model the interconnection of wind farms to study the transient characteristics. The three wind farms are interconnected at a single point on the transmission line to increase efficiency and reliability. Analysis on voltage stability of wind farms due to faults on the neighbouring wind farm was done. A STATCOM was installed at the terminals of each wind farm to provide additional voltage stability and reactive power capabilities.

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+ Evolution Of Plasma Density Generated By High Power Microwaves
  S. Beeson; A. Neuber
Abstract:  The relaxation time of pulsed rf-generated plasma is investigated. A 3 MW, 3 μs width, 50 ns risetime HPM pulse is transmitted through a dielectric window that terminates a WR-284 waveguide filled with insulating gas. The investigated plasma is formed across the dielectric window on the atmospheric side. This produces electron densities on the order of 1013 to 1012 cm-3 for 60 to 145 torr in air, respectively. In the same pressure range, initial attenuation (~ 0.5 dB) of the microwaves is observed after tens to hundreds of nanoseconds with final attenuation values approaching -40 to -10 dB, respectively. To determine plasma relaxation times after the HPM pulse terminates a multi-standard waveguide coupler (X/S-band) was designed to inject a low power 10 GHz signal used for probing the surface plasma. The coupler was designed to have high coupling coefficients (> -5 dB) for the specific narrowband around 10 GHz (BW ~ 10 MHz) along with negligible insertion loss of the HPM propagation. From the measured attenuation and reflection of the 10 GHz probe signal, the evolution of the electron density is inferred. Furthermore, in an air environment, the density falls exponentially implying attachment as the dominate electron loss mechanism.

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+ Experimentation And Simulation Of High Current Density Surface Coated Electro-Explosive Fuses
  J. C. Stephens; A. A. Neuber; J. C. Dickens; M. Kristiansen
Abstract:  The primary objective of the research discussed in this paper is to develop a compact electro-explosive fuse (EEF) for a flux compression generator (FCG) power conditioning system, capable of rapidly obtaining and maintaining high impedance. It was observed that significant gains in EEF performance are introduced with the application of an insulating coating to the surface of the EEF wire. A 2 kA small scale test bed has been designed to provide a single wire EEF with similar current density (~107 A/cm2), voltage gradient (~7 kV/cm), and timescale (~8 μs) as to what is seen by and EEF utilized in a HPM generating FCG system. With the small scale test bed EEF performance data was rapidly obtained at a significantly lower cost than equivalent full scale FCG experiments. A one-dimensional finite difference model coupled with the Los Alamos National Laboratory SESAME Equation-of-State database was utilized to simulate the resistive behavior of the single wire EEFs. Further, a large scale test bed, designed to provide a similar current action as to what is provided by a FCG is used to test 18 wire EEF arrays at the 40 kA level.

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+ Fiber Optic System For High Frequency Burst Operation Of A Silicon Carbide Photoconductive Semiconductor Switch
  Mauch, D; Hettler, C; Sullivan, WW; Dickens, J
Abstract:  A fiber optic system was constructed to demonstrate high frequency operation of a silicon carbide (SiC) photoconductive semiconductor switch (PCSS). The goal was to transform a single high-energy laser pulse into a train of pulses by adding static delays into a multimode fiber bundle. The individual optical fibers comprising the fiber bundle incrementally add an additional amount of flight time to the light pulse. The end result is a train of pulses with a fixed delay between each pulse. A frequency-tripled Nd:YAG laser (10 ns FWHM) generating up to 300 mJ of light energy at 355 nm is coupled from free space into the optical fibers comprising the fiber light guide. Experimental results examining the collection and transmission efficiency, and the temporal output are presented.
+ Flywheel Energy Storage Systems For Wind Turbine Grid Frequency Stability - A Review
  Durukan, I; Ekwaro-Osire, S; Bayne, SB
Abstract:  Most recent grid codes require wind turbines to contribute to the recovery of frequency drops in the grid. More of the recently build wind turbines use variable speed generators. Unlike fixed speed generators, these generators do not naturally contribute to the recovery of the frequency drop since the rotor rpm is decoupled from the grid frequency. This decoupling is achieved by controller and power conditioning units. The studies reviewed in this paper focused on the design of such a controller so that the wind turbine could react to frequency drops. Another approach to responding to frequency drops is to connect an energy storage system to the DC bus of variable speed generator. Flywheels have been used as energy storage systems to fill energy gaps in several applications and can be used for frequency recovery application for wind turbines as well. The objective of this study was to demonstrate the improvement of frequency stability of wind turbines connected to electrical grids in the presence of flywheel energy storage systems (FESS). Studies reviewed show that FESS can enhance the power quality and frequency stability of wind turbines connected to an electrical grid.
+ Frequency Agility Of A Ferrite-Loaded, Nonlinear Transmission Line
  C. Simmons; J. -. B. Bragg; J. Dickens; A. Neuber
Abstract:  A nonlinear transmission line (NLTL) provides a solidstate means of generating high power, microwave pulses. The NLTLs in this study are coaxial transmission lines whose center conductor is encapsulated by ferrite beads. Operational frequency can be controlled by varying the dimensions of the ferromagnetic material, which affects azimuthal magnetic fields and material losses, or by varying the biasing field strength. This research demonstrates frequency agility of an NLTL by documenting the design, construction, and testing of three NLTLs. The NLTL will be one meter long, and to test for frequency agility, three different sizes of ferrites will be loaded onto NLTL with various biasing fields applied. Azimuthal field strengths due to an incident high voltage pulse range from 10-36 kA/m with magnetic biasing fields between 0 kA/m and 50 kA/m.

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+ Gas Evolution Of Nickel, Stainless Steel 316 And Titanium Anodes In Vacuum Sealed Tubes
  J. Parson; J. Dickens; J. Walter; A. Neuber; M. Kristiansen
Abstract:  This paper presents a study on gas evolution of three different anode materials in vacuum sealed tubes under UHV conditions. The experimental apparatus consists of a high-power microwave (HPM) virtual-cathode oscillator (vircator) driven by a 200 ns, 80 J, 225 kV low-impedance Marx Generator. Plasma expansion due to explosive electron field emission has shown to lower gap impedance, spoil consistent low vacuum levels, and cut-off microwave radiation. The anode materials compared are nickel 201L (Ni201L), stainless steel 316L (SS316L) and grade-1 titanium (TiG1); with the cathode material being aluminum. The anodes were cleaned by the following method: rough polishing followed by electro-polishing, a ten minute microwave argon / 10% oxygen plasma cleaning process (ArO2) and finally, a 72 hour in situ bake-out at 300°C. Outgassing characteristics of each anode material are presented and compared.

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+ Investigation Of Vacuum Uv Absorption During Low-Temperature Plasma Formation In N2/H2 Mixtures At Atmospheric Pressure
  G. Laity; A. Neuber; A. Fierro; L. Hatfield; J. Dickens; K. Frank
Abstract:  This paper describes recent advances in the study of self-generated emission of vacuum ultraviolet (VUV) radiation which is produced during the early time period leading to high voltage breakdown at atmospheric pressure. Previous studies of air breakdown showed the presence of 121.5 nm radiation which is spontaneously emitted by excited hydrogen atoms, HI. Since this Lyman-α line is self-absorbed, it enabled inferring various plasma parameters from recording emission spectra from 115-135 nm for species of HI and NI. For instance, measurements in H2/N2 mixtures have revealed that the highest amount of absorption via HI atoms occurs in the high field region near the anode, implying that significant H2 dissociation for radiation-trapping is occurring in this zone. Selective spatial measurements further showed that the apparent VUV emission centers (i.e. streamer heads) move away from the anode and the mechanisms leading to line broadening (i.e. Stark effect from space charge) are a function of streamer position. The presented self-absorption mechanisms are essential in quantitatively understanding the role of VUV radiation transport via absorption for photo-ionization during streamer breakdown, in which re-absorption of high energy photons is inherently a requirement.

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+ Multiple Resource Expansion Planning In Smart Grids With High Penetration Of Renewable Generation
  Cao, Y; He, M; Wang, ZQ; Jiang, T; Zhang, JS
Abstract:  We study joint expansion planning of conventional generation capacity, wind generation capacity and tie line capacity in a multi-area smart grid system. Specifically, we formulate the expansion planning problem as a two-stage stochastic programming problem: 1) in the first stage, resource expansion plans are made to minimize the expected overall cost throughout the entire planning horizon; 2) in the second stage, given the realization of load and wind generation in hourly scheduling slots, optimal scheduling decisions of power flows are found by minimizing the cost incurred by conventional generation and/or loss of load, which is used to compute the expected operation cost and/or loss of load cost as part of the cost in the first stage. In particular, the optimal solution to the resource expansion planning problem is obtained using the L-shaped algorithm. The simulation results of several case studies indicate that the optimal expansion plans for a multi-area smart grid indeed depend on the uncertainty level of prospective wind generation, the existing generation capacity and the transmission capacity.
+ Performance And Optimization Of A 50 Kv Silicon Carbide Photoconductive Semiconductor Switch For Pulsed Power Applications
  C. Hettler; W. W. Sullivan; J. Dickens; A. Neuber
Abstract:  A 50 kV silicon carbide photoconductive semiconductor switch (PCSS) is presented. The SiC PCSS device is fabricated from semi-insulating 4H-SiC in a newly-proposed rear-illuminated, radial switch structure. The improved structure reduces the peak electric field within the switch, extending the blocking voltage to over 50 kVdc. Electrostatic field simulations of the PCSS are presented along with experimental blocking curves. The PCSS demonstrated low on-state resistance, delivering over 27 MW of peak power into a 31 Ω load. Device modeling was performed to further optimize the switch for peak efficiency when illuminated with 355 nm light, a common laser wavelength. The switch structure was modified for peak operation at 355 nm and the experimental and theoretical results are compared.

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+ Power Quality Analysis Of A Sensitive Load Using A Phasor Measurement Unit
  S. Pappu; A. Rahnama; M. Tovar; S. Bayne; B. Little; S. Friend; M. Borhani
Abstract:  This paper discusses the set up and analyses of Power Quality using a Phasor Measurement Unit (PMU) located at a Semiconductor Foundry Fabrication Facility (sensitive load). The paper demonstrates the setting up of an SEL 421 PMU at the Facility (software and hardware), data archiving and real time waveform capture of voltages, currents and frequency. A code was developed for filtering the data collected from the PMU in MATLAB. A GUI was developed in MATLAB. The GUI analyses the data from the PMU and highlights aberrations in the values of Voltages and Frequency from the Power Quality limits for sensitive loads. The paper evaluates a unique method for analysis of Power Quality before the installation of a wind turbine directly feeding the Facility so as to set a standard after the wind turbine is installed.

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+ Pspice Modeling Of Silicon Carbide Mosfets And Device Parameter Extraction
  A. Bilbao; S. Bayne
Abstract:  The goal of this research is to develop device models for Silicon Carbide (SiC) MOSFETs. Parameters are extracted and used to create PSPICE models that can be utilized for circuit simulation. Two silicon carbide power MOSFETs made available by CREE Semiconductor are considered. The first silicon carbide power MOSFET tested is the CMF20120A64410. This MOSFET features a 1200V drain-to-source breakdown voltage and 30A continuous current capacity. The second device tested is an experimental MOSFET that is still not available in the market as of the date of this paper. The experimental MOSFET features a 1200V drain-to-source breakdown voltage and 80A continuous current capability. Custom made circuits are developed for extracting some of the parameters. In some cases where the tests only require low drain current, a HP B1505A curve tracer is used to aid the development of the model. The effect of temperature over the gate threshold voltage is also investigated. By externally increasing and monitoring the die temperature of the SiC MOSFETs, new device parameters can be extracted and modeled. Once the parameters are extracted they are converted into a PSPICE model. The model is tested and compared to the real device to verify accuracy. This is achieved using custom switching circuits with both inductive and resistive loads and software suites like MATLAB.

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+ Rapid Capacitor Charging Power Supply For An 1800J Pfn
  T. T. Vollmer; M. G. Giesselmann
Abstract:  The RCC (rapid capacitor charger) previously developed at the P3E Center [1] has been adapted to charge an 1800 J PFN (pulse forming network) for rep-rated operation. The entire automated system to test and evaluate SGTOs (Super Gate turn-off Thyristors) runs at a 1 Hertz repetition rate; thus requiring a power supply to charge the PFN within 500 ms and have a 3.6 kJ/s average power capability to allow for data acquisition and storage between shots. The hard-switching H-bridge topology with 10 kW burst mode handling capability is very well suited for this compact table top system design. The control of the RCC has been shifted to a PIC controller responsible for PFN charging. Charging parameters include: an adjustable charging time from 50 to 500 ms, high voltage monitoring with adjustable voltage level, and RCC Go/shut-off. All charging parameters are determined by the main CPU handling the automation process and are sent to the PIC controller before each PFN charging event. With the addition of forced air cooled heat-sink for the IGBT modules, enough heat can be removed to allow continuous automated operation.

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+ Reliable Operation Of 1200-V Sic Vertical Junction-Field-Effect-Transistor Subjected To 16,000-Pulse Hard Switching Stressing
  Lawson, K; Alvarez, G; Bayne, SB; Veliadis, V; Ha, HC; Urciuoli, D; Scozzie, C
Abstract:  A necessity for the successful commercialization of SiC power devices is their long term reliability under the switching conditions encountered in application. Normally-ON 1200 V SiC JFETs were stressed in hard-switching conditions to determine their fault handling capabilities. The hard-switching included single shot tests ranging from drain voltages of 100 V to 500 V and repetition rate tests at 1 Hz, 5 Hz, 10 Hz, and 100 Hz with peak currents exceeding 100 A (8 times the rated current at 250 W/cm(2)). The JFET conduction and blocking-voltage characteristics are unchanged after 16,000 pulsed and numerous single shot hard switching events proving the devices are reliable for handling high surge-current faults.
+ Serial Arrangement Of Ferrimagnetic Nonlinear Transmission Lines
  J. -. B. Bragg; C. Simmons; J. C. Dickens; A. A. Neuber
Abstract:  Nonlinear transmission lines (NLTLs) utilizing ferrimagnetic materials for microwave generation have been realized as a possible solid-state replacement to traditional high power microwave (HPM) sources. The nonlinearities present in the material, along with interaction between pulsed, azimuthal magnetic fields and static, axial-biasing magnetic fields provide microwave (mesoband) generation with peak powers exceeding 30 MW at 2-4 GHz center frequency with 25 kV incident pulse magnitude. Additionally, an incident pulse of several nanoseconds is sharpened to hundreds of picoseconds. This study focuses on a serial arrangement of two NLTLs with 5 ns electrical length separation. Tests with 25 kV incident voltage are performed with varying bias schemes for each NLTL structure. The lines are terminated into a 50 Ω matched load. Measurements taken before and after each NLTL provide insight to the behavior of the traveling pulse. Results regarding peak power, frequency of operation, and system delay are discussed.

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+ Shallow Incorporation Of Nitrogen In Hpsi 4H-Sic Through The Laser Enhanced Diffusion Process
  Sullivan, W; Hettler, C; Dickens, J
Abstract:  This paper investigates n-type doping of point-defect compensated high purity semi-insulating (HPSI) 4H-SiC using a pulsed laser (10 ns FWHM @ 260 nm) for the introduction of nitrogen to shallow depths. A thermal model is presented using COMSOL Multiphysics featuring nonlinear temperature dependent material properties and a volumetric heat source term that takes into account the laser absorption depth for common ultraviolet irradiating wavelengths. The temperature distribution in the material and the amount of time that the surface and near-surface regions are at high temperature determines how many laser pulses are required to dope to the desired depth, and simulation results are presented and fit to measured data. The simulations and measured data show that for shallow doping a short wavelength ultraviolet laser should be used to localize the heat at the surface so the dopant can't diffuse deep into the material. The laser enhanced diffusion process has been used to incorporate nitrogen into HPSI 4H-SiC with a measured surface concentration greater than 10(20) cm(-3) and a nonlinear thermal model was built.
+ Simulation Of An Exploding Wire Opening Switch
  J. C. Stephens; A. A. Neuber; M. Kristiansen
Abstract:  An exploding wire model that accounts for the electric field enhanced conductivity of dense metal plasma is applied to simulate an exploding wire opening switch. In contrast to many z-pinch experiments, operated in vacuum, the experiments here discuss wires vaporized in a high pressure gas environment. In addition to this, these experiments are primarily concerned with sub-eV temperatures, with a specific emphasis on the liquid-vapor phase transition, where significant decreases in conductivity provide the opening switch behavior. It is common that fuses operating within this regime are analyzed using 0-dimensional models, where the resistance is taken to be an experimentally determined function of energy or action. A more accurate 1-dimensional model with added field enhanced conductivity has been developed to better model the fuse dynamics throughout a significantly larger parameter range. The model applies the LANL SESAME database for the equation-of-state, and the conductivity data developed with the Lee-More-Desjarlais (LMD) algorithm. Using conductivity based on conditions of thermal equilibrium accurately predicts fuse opening as well as current re-emergence after a few microseconds dwell time for the case of small electric fields, however, this simple approach fails to capture early fuse restrike if the differential voltage across the wire becomes too large (~few kV/cm for the investigated conditions). It is demonstrated that adding an electric field driven conductivity term to the model will accurately capture the fuse dynamics for the low field as well as the high field case.

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+ Spatially-Resolved Spectral Observations Of Pulsed Surface Flashover In A Nitrogen Environment
  A. Fierro; G. Laity; A. Neuber; L. Hatfield; J. Dickens
Abstract:  The development of streamers during the initial stage of a pulsed atmospheric discharge, which carries a high content of vacuum UV (VUV) emission, is investigated. Due to the high spectral absorptivity of atmospheric air in the VUV regime, few experiments have been conducted that observe the wavelength range shorter than 180 nm. However, direct photoionization is believed to play an important role in streamer formation during this phase of breakdown. VUV radiation (hν > 7 eV) is energetic enough to promote step-ionization and directly ionize background gas mixtures. Utilizing a VUV-sensitive experimental apparatus, spatially-resolved photomultiplier tube (PMT) measurements were recorded showing that initial VUV emission is dependent on the inhomogeneous field distribution near the electrodes. It was revealed that further into the developing streamer the position of instantaneous VUV emission is propagating from anode to cathode away from the initial VUV emissions. From these observations, the low temperature plasma is capable of producing high energy photons during the streamer phase as well as after voltage collapse.

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+ Susceptibility Of Electro-Explosive Devices To High Pulsed Electric Fields
  D. V. Reale; J. Mankowski; J. Dickens
Abstract:  Commercially available Electro-Explosive Devices (EEDs), such as blasting caps, use electrical current to initiate a primary charge. Various detonators including bridge wire, match-type, exploding bridge wire, and slapper. The basic operating principle of the match-type device is to heat the ignition element to the ignition temperature of the primary explosive. The normal operation current profiles, both constant current and pulsed excitation, are well known, as is the ignition temperature. However, as safety and reliability are of great concern, both in the operation and storage of EEDs, the susceptibility of these devices to transient or spurious fields is of interest. The susceptibility of match-type EEDs to high pulsed electric fields is examined. A Finite Element Method (FEM) simulation is performed using COMSOL to determine the induced current in the bridgewire due to applied electric fields and the resulting Joule heating of the wire. Several situations are investigated including the EED in conductive and non-conductive media and leads open or terminated representing operational and storage conditions.

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+ The Effects Of Sub-Contact Nitrogen Doping On Silicon Carbide Photoconductive Semiconductor Switches
  Sullivan, W; Hettler, C; Dickens, J
Abstract:  Forming non-rectifying (ohmic) contacts to wide band gap semiconductors such as silicon carbide (SiC) requires a heavily doped subsurface layer to reduce the Schottky barrier height and allow efficient electron injection. Nitrogen, a common n-type dopant in SiC, was incorporated into a SiC sample using a laser enhanced diffusion process in which an impurity is incorporated into the semiconductor to very high surface concentrations (> 10(20) cm(-3)) and very shallow depths (< 200 nm) with the use of a pulsed 266 nm laser. This paper evaluates the effects of nitrogen introduced through laser enhanced diffusion on the contact formation and the efficiency of silicon carbide photoconductive switches at low and high injection levels under different biasing conditions. Nine lateral switches were fabricated on a high-purity semi-insulating 4H-SiC sample; three with no sub-contact doping, three with sub-contact doping on only one contact, and three with sub-contact doping on both contacts. Results are presented for tests under pulsed laser illumination with sub-contact doping on only the anode, only the cathode, neither, and on both of the contacts.
Publication Year:  2011
+ A New Similarity Measure Based Robust Possibilistic C-Means Clustering Algorithm
  Jia, KX; He, M; Cheng, T
Abstract:  In this paper, we focus on the development of a new similarity measure based robust possibilistic c-means clustering (RPCM) algorithm which is not sensitive to the selection of initial parameters, robust to noise and outliers, and able to automatically determine the number of clusters. The proposed algorithm is based on an objective function of PCM which can be regarded as special case of similarity based robust clustering algorithms. Several simulations, including artificial and benchmark data sets, are conducted to demonstrate the effectiveness of the proposed algorithm.
+ Adaptive Combination Of Subband Adaptive Filters With Selective Partial Updates
  Liu, C; He, M; Xia, W
Abstract:  Combining the concepts of adaptive combination and selective partial updates (SPU) in the normalized subband adaptive filter (NSAF), an adaptive combination of two NSAFs with SPU (SPU-CNSAF) is presented. The proposed scheme not only reduces the computational complexity but also provides a good convergence performance. Simulation results show the efficiency of the proposed scheme. In addition, the SPU concept can also be extended to some other combination schemes such as the combination of normalized least mean square (NLMS) filters, recursive least squares (RLS) filters and affine projection (AP) filters.
+ Bioheat Model Evaluations Of Laser Effects On Tissues: Role Of Water Evaporation And Diffusion
  Nagulapally, D; Joshi, RP; Thomas, RJ
Abstract:  A two-dimensional, time-dependent bioheat model is applied to evaluate changes in temperature and water content in tissues subjected to laser irradiation. Our approach takes account of liquid-to-vapor phase changes and a simple diffusive flow of water within the biotissue. An energy balance equation considers blood perfusion, metabolic heat generation, laser absorption, and water evaporation. The model also accounts for the water dependence of tissue properties (both thermal and optical), and variations in blood perfusion rates based on local tissue injury. Our calculations show that water diffusion would reduce the local temperature increases and hot spots in comparison to simple models that ignore the role of water in the overall thermal and mass transport. Also, the reduced suppression of perfusion rates due to tissue heating and damage with water diffusion affect the necrotic depth. Two-dimensional results for the dynamic temperature, water content, and damage distributions will be presented for skin simulations. It is argued that reduction in temperature gradients due to water diffusion would mitigate local refractive index variations, and hence influence the phenomenon of thermal lensing. Finally, simple quantitative evaluations of pressure increases within the tissue due to laser absorption are presented.
+ Compact Electro-Explosive Fuse Optimization For A Helical Flux Compression Generator
  J. C. Stephens; A. A. Neuber; J. C. Dickens; M. Kristiansen
Abstract:  This paper presents the optimization of a compact electro-explosive fuse designed for the power conditioning system to be driven by a helical flux compression generator (HFCG). An electro-explosive fuse interrupts the current flow from the HFCG through a storage inductor on a 50 to 100 ns timescale inducing a voltage large enough to close a peaking gap, which commutates the energy in the storage inductor into a 20 Ohm load at voltage levels above 200 kV. Experimental data has revealed that electro-explosive fuses with wires in closer proximity to one another have consistently produced lower pulsed voltages than fuses with larger wire spacings. This paper addresses possible factors that might contribute to this drop in performance. An electro-magnetic field solver is used to model the current redistribution in the fuse wires. The experimentally observed performance of compact fuses with varying wire spacings is presented.

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+ Comsed 2 - Recent Advances To An Explosively Driven High Power Microwave Pulsed Power System
  M. A. Elsayed; A. A. Neuber; J. W. Walter; A. J. Young; C. S. Anderson; S. L. Holt; J. Dickens; M. Kristiansen; L. L. Altgilbers
Abstract:  Continued efforts at the Center for Pulsed Power and Power Electronics at Texas Tech University have led to improvements to the design, testing, and performance of a high power microwave (HPM) system, which is sourced by Lithium-ion Polymer batteries, a polypropylene capacitor, and high energetics. An indirectly seeded two-stage helical flux compression generator (HFCG) produces electrical energies in the kilo-Joule regime into a low impedance inductive load, varying from 2 μH to 3 μH. This high current output of the explosively driven generator is conditioned with a pure silver-wire-based electro-explosive opening switch, which reaches voltage levels in excess of 300 kV into a 18 Ohm load. Upon reaching levels high enough to close an integrated peaking switch, this high voltage is sufficient to drive a reflex triode virtual cathode oscillator, also known as a Vircator, into radiation. The Vircator employed in the system has reached microwave radiation levels well over 100 Megawatts from a cavity volume of less than 5 Liters at a microwave frequency of a few GHz. The complete system is governed through a microcontroller that regulates seed and detonator charging levels as well as discharge times using built-in feedback diagnostics. The complete system aforementioned is constrained to 15 centimeter diameter and measures 183 centimeter in length with an overall volume of less than 34 Liters. No external power or vacuum pumping for the HPM tube is required. This report will discuss recent design advancements and improvements on the HPM system and its sub-components that include the compact seed source, HFCG, and the power conditioning system. Improved safety features implemented as well as novel diagnostic integration will be discussed as well.

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+ Evaluation Of Experimental Silicon Sgto Devices For Pulsed Power Applications
  S. Lacouture; S. B. Bayne; M. G. Giesselmann; K. Lawson; H. O'Brien; C. J. Scozzie
Abstract:  The development of new semiconductor devices requires that extensive testing be completed in order to fully understand the device characteristics and performance capabilities. This paper describes the evaluation of experimental Silicon high power Super Gate Turn Off Thyristors (Si SGTOs) in a unique testing environment. The SGTOs are capable of blocking in the forward direction up to 5kV and are also capable of handling several kA when pulsed. The device structure is asymmetric so the reverse blocking of these devices is only a couple hundred volts. Since these devices are SGTOs special consideration had to be given to the gate trigger circuit so that noise would be minimized on the gate therefore preventing false triggering of the devices.

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+ False Alarm Probability Of The Digital Channelized Receiver Based Ca-Cfar Detector
  He, M; Jia, KX; Cheng, T
Abstract:  This paper studies the effect of the correlated noise responses on the false alarm probability of the digital channelized receiver based CA-CFAR detector. The statistic characteristics of the digital channelized receiver are firstly discussed in additive white Gaussian noise. Two different expressions are then derived for the false alarm probability of the CA-CFAR detector when the noise responses are correlative and assumed independent, respectively. Finally, the above expressions are compared by simulation. The simulation experiments show that the detection performance of the CA-CFAR detector in assumed conditions is very similar to the one in practical conditions. Hence, the assumption that the noise responses are statistically independent is reasonable in practical engineering.
+ Modeling And Control Of Directly Connected And Inverter Interfaced Sources In A Microgrid
  M. Chamana; S. B. Bayne
Abstract:  There has been a keen interest on Distributed Generation (DG) due to their restricted goals of meeting local loads and improving reliability of the overall system. Microgrids (MGs) are connected to the main grid through a Point of Common Coupling which separates the former from the latter. At the time of an intentional islanding or fault at the grid level, a microgrid is able to disconnect itself from the rest of the grid and operate by itself. A microgrid may contain both directly connected and inverter interfaced sources with different control configurations. When disconnected or islanded from the main grid there are various approaches to share the load, one of them being master-slave control where a storage device may become the reference DG to set the nominal voltage and frequency. When the main grid is brought back to normal operation, the microgrid is able to resynchronize itself to the main grid only when it meets certain conditions so as to avoid transients. All the microsources, power electronics and their control with power management were developed in Matlab/Simulink.

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+ Modeling, Control And Power Management Of Inverter Interfaced Sources In A Microgrid
  M. Chamana; S. B. Bayne
Abstract:  Microgrid is a combination of Distributed Energy Resources (DERs) and loads that are connected within a locality. Microgrids are connected to the main grid through a Point of Common Coupling (PCC) which separates the former from the latter. In grid connected mode all the Distributed Generators (DGs) are PQ controlled with pre-defined set-points and the power imbalance is imported from or exported to the main grid. At the time of an intentional islanding or fault at the main grid level, a microgrid is able to disconnect itself from the rest of the grid and operate by itself. A microgrid may contain both directly connected and inverter interfaced sources with different control configurations. When disconnected or islanded from the main grid there are various approaches to share the load, one of them being the master-slave control where a storage device (battery) becomes the reference DG to set the nominal voltage and frequency for the entire microgrid. The State Of Charge of the battery is considered for the battery dynamics when in islanded mode for bi-directional flow. All the microsources, power electronics and their control with power management were developed in Matlab/Simulink.

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+ Multiple Timescale Dispatch And Scheduling For Stochastic Reliability In Smart Grids With Wind Generation Integration
  He, M; Murugesan, S; Zhang, JS
Abstract:  Integrating volatile renewable energy resources into the bulk power grid is challenging, due to the reliability requirement that the load and generation in the system remain balanced all the time. In this study, we tackle this challenge for smart grid with integrated wind generation, by leveraging multi-timescale dispatch and scheduling. Specifically, we consider smart grids with two classes of energy users - traditional energy users and opportunistic energy users (e.g., smart meters or smart appliances), and investigate pricing and dispatch at two timescales, via day-ahead scheduling and real-time scheduling. In day-ahead scheduling, with the statistical information on wind generation and energy demands, we characterize the optimal procurement of the energy supply and the day-ahead retail price for the traditional energy users; in real-time scheduling, with the realization of wind generation and the load of traditional energy users, we optimize real-time prices to manage the opportunistic energy users so as to achieve system-wide reliability. More specifically, when the opportunistic users are non-persistent, we obtain closed-form solutions to the two-level scheduling problem. For the persistent case, we treat the scheduling problem as a multi-timescale Markov decision process. We show that it can be recast, explicitly, as a classic Markov decision process with continuous state and action spaces, the solution to which can be found via standard techniques.
+ New Asic Architecture Development For Energy Harvesting
  D. Reddy; N. S. Beniwal; S. B. Bayne
Abstract:  This paper presents the design of an ultra-low power energy scavenging system capable of collecting and managing energy from ambient vibrations and RF electromagnetic waves. Firstly, low power and broadband equiangular spiral antenna which is able to receive and rectify ambient RF radiation is designed and simulated. The energy transducers, commercial piezoelectric generators with a wide frequency range of 26 "“ 205Hz and the designed spiral antenna are evaluated and characterized to maximize the efficiency. Secondly, the power electronic circuits involved in the energy harvesting are designed in 0.6um CMOS technology and the simulation results are presented. Charge pumps, rectifier and Low drop-out regulator (LDO) were optimized to operate with low voltage ranges since the energy produced by the piezoelectric generator and the equiangular spiral antenna is found to be in microwatts and less from the test results. The AC output from the piezoelectric generator is rectified and boosted to required output level using an AC-DC charge pump. Rectifier and DC-DC charge pump are adopted for the efficient conversion of voltage from the broadband antenna. A back-up battery is provided for the start-up of DC-DC charge pump at low input conditions. An LDO with a drop-out voltage of less than 400mV is designed to provide regulated output of 4.1V to the battery. Finally, the collected energy is stored in a 50uAh capacity thin film battery which is intended for low-voltage and low-power applications.

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+ Rep-Rated Operation Of A Modular, Compact Hv-Capacitor Charger
  T. T. Vollmer; M. G. Giesselmann
Abstract:  We are reporting results on a compact high voltage capacitor charger with modular topology for rep-rated operation. This modular topology utilizes synchronized hard-switching H-Bridge inverters. Each current-mode controlled inverter is fed into the highly coupled primaries of a high frequency transformer with a nano-crystalline core. This charging system with two synchronized H-Bridges has reached voltages of over 20 kV with power outputs in excess of 10 kW. Rep-rated operation along with system efficiency has been explored with this modular topology system. Burst mode operation has achieved rep rates close to 20 Hz. Overall system efficiencies have been measured at nearly 80%.

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+ The Effects Of Insulation Material And Methods Of Fabrication On The Performance Of Compact Helical Flux Compression Generators
  C. S. Anderson; A. A. Neuber; A. J. Young; J. T. Krile; M. A. Elsayed; M. Kristiansen
Abstract:  Helical Flux Compression Generators, HFCGs, are powerful high current sources for pulsed power applications. Due to the single shot nature of HFCGs, electrical output reproducibility is of great importance. One factor known to contribute to unpredictable performance is mechanical inconsistencies introduced during manufacturing of the stator. In an attempt to minimize these deviations during productions, two different winding forms for stator coils, designed to ensure repeatable generator dimensions, turn and coil pitch, were investigated. The differences between the methods were quantified by comparison of measurements made of the physical parameters of the coil (i.e. radius, inductance, etc.), as well as analysis of experiments conducted with the HFCGs fired into a 3 μH load inductor. With any particular fabrication method, the stator insulation material has a distinct impact on generator operation. Quad-built Polyimide coated magnet wire as stator insulation material and Teflon Fluorinated Ethylene Propylene (FEP) as field coil insulation material were investigate to improve HFCG performance. Insulation testing was carried out by firing HFCGs into the inductive load mentioned above. Experimental data and analysis, as well as conclusions on insulation material, will be presented along with a brief discussion of the optimum fabrication method.

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+ Unique High Energy Test Bed For Experimental Thyristor Devices
  S. Lacouture; S. B. Bayne; M. G. Giesselmann; K. Lawson; H. O'Brien; C. J. Scozzie
Abstract:  This paper details the design of a test platform for experimental silicon and silicon carbide Super Gate Turn Off devices (SGTOs) capable of stressing the devices with very high energy/power levels while at the same time mimicking a realistic, real world application. To this end an aircraft ground power Motor - Generator set was acquired consisting of a high frequency synchronous generator, a D.C. powered brushless exciter machine, and a 100 HP induction motor. The Si SGTO devices were then placed in a three phase controlled rectifier circuit connected between the generator output and a low impedance high power purely resistive load.

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Publication Year:  2010
+ An Investigation Of Pulsed High Power Microwave Surface Flashover Initiation In Atmospheric Conditions
  J. Foster; M. Thomas; J. Krile; H. Krompholz; A. Neuber
Abstract:  The production of high power microwaves (HPM) in a vacuum environment for the purpose of radiating into atmosphere requires the use of a dielectric interface to separate the vacuum and atmospheric sides of the radiating structure. For high power to pressure ratios the interface will exhibit surface flashover on the atmospheric side, thus limiting the transmission of microwave power. An experimental setup that utilizes a magnetron operating at 2.85 GHz to produce a 4.5 MW, 3μs pulse propagating in the TE10 mode along with an atmospheric test chamber enables investigating HPM surface flashover phenomena in the presence of various atmospheric conditions. One of the principle parameters measured is the delay time between application of the microwave pulse (50 ns rise time) and the sharp drop in transmitted power due to the flashover plasma formation. Several methods of delay time reduction have been employed to gain a better understanding of the source of breakdown initiatory electrons. For an environment composed of air at, for instance, 155 torr a delay time of 600 ns is observed. Illuminating the dielectric surface with continuous UV radiation reduces the average delay to about 380 ns. An even more distinct reduction in delay time was observed when electric field enhancement was introduced to the window surface via vapor deposition of sub-mm metallic points on the dielectric. These metallic points have proven to reduce the delay time to ~150 ns while increasing the global effective electric field by a factor of ~1.5. This presentation will include an overview of a variety of methods for investigating flashover initiation, including UV radiation and the application of an external DC electric field, as well as the introduction of field enhancing metallic points on the dielectric surface. An analysis of flashover behavior at atmospheric pressures (60-155 torr) in air, argon, and nitrogen will also be given along with an estimation of field enhancement factors for various geometries.

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+ Characterization Of A 50 J Linear Transformer Driver
  D. Matia; H. Krompholz; T. Vollmer; A. Neuber; M. Giesselmann; M. Kristiansen
Abstract:  A detailed characterization of a 50 J linear transformer driver (LTD) stage is presented. The specific goal of the design is to achieve energy densities superior to typical Marx generators, such as a 500 J compact Marx generator previously designed and built at Texas Tech's Pulsed Power lab. Experimental and analytical techniques for determining circuit elements and especially parasitic elements were used, yielding the magnetizing, primary and secondary leakage inductances associated with the transformer, core saturation effects, parasitic capacitances, the inductance of the pulse discharge circuit, and losses in both copper and the deltamax core. The investigations into these characteristics were carried out using both sinusoidal excitation from 1 kHz to 20 Mhz, and pulsed excitation with rise times down to 5 ns. Pulse amplitudes were varied to cover both the linear and saturation regimes of the core. Distributed parasitic capacitances and the inductance of the pulse discharge circuit were estimated analytically and compared with experimental results. This work was carried out to seek an ideal arrangement of the capacitors and switches on the LTD stage and gain a better basic understanding of fast rise time pulse transformers. Adjustments to the 50 J stage are proposed based on this characterization in order to optimize a future ten stage, 500 J assembly.

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+ Fault Detection And Localization In Smart Grid: A Probabilistic Dependence Graph Approach
  He, M; Zhang, JS
Abstract:  Fault localization in the nation's power grid networks is known to be challenging, due to the massive scale and inherent complexity. In this study, we model the phasor angles across the buses as a Gaussian Markov random field (GMRF), where the partial correlation coefficients of GMRF are quantified in terms of the physical parameters of power systems. We then take the GMRF-based approach for fault diagnosis, through change detection and localization in the partial correlation matrix of GMRF. Specifically, we take advantage of the topological hierarchy of power systems, and devise a multi-resolution inference algorithm for fault localization, in a distributed manner. Simulation results are used to demonstrate the effectiveness of the proposed approach.
+ Hardware-In-The-Loop Testing Of Gm Two-Mode Hybrid Electric Vehicle
  T. Maxwell; K. Patil; S. Bayne; R. Gale
Abstract:  This paper presents Hardware-in loop (HIL) testing for GM two-mode hybrid. First Modeling and simulation of GM two-mode hybrid using model based design (MBD) process is performed. HIL testing is performed using dSpace MicroAutoBox (MABX) and National Instruments PXI. The control strategy compiled code is uploaded to MABX using ControlDesk software and the corresponding plant model is transferred to PXI using NI Veristand software. This work is part of EcoCAR competition by the Texas Tech University. EcoCAR: The Next Challenge is a vehicle engineering competition organized by the US Department of Energy (DOE) and General Motors (GM).

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+ Modular, Compact Hv-Capacitor Charger
  M. G. Giesselmann; T. T. Vollmer; L. Altgilbers
Abstract:  We are reporting on a new compact high power capacitor charger with modular topology for rep. rated High Power Microwave generators and other Pulsed Power Applications. The charger is capable of using a number of synchronized H-Bridge inverters feeding into a common transformer. The common transformer uses litz wire windings and a nano-crystalline core to reduce losses and AC impedance. The H-Bridge inverter modules are individually controlled using peak current mode control which assures proper current sharing and protects the H-Bridge modules from overload while achieving the maximum current handling capacity. To assure stability of the current loops for peak current mode control, slope compensation is used. Major advancements over previous designs are the ability to use multiple H-Bridge inverters with proper synchronization, improved efficiency through advanced transformer design and improved current mode control.

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+ Reducing Semiconductor Process Tool Resource Usage "“ Pilot Project Results
  P. Hawkins; A. Neuber; K. Vepa
Abstract:  Applied Materials is working with customers to assess new ways to identify opportunities to reduce resources usage (energy, process chemicals/gasses) by existing semiconductor process tools. Through six customer pilot projects we have identified potential average savings of $22.5K per year, for the CMP and CVD process tool examined, by using a consultative service approach to business and financial analysis that pinpoints opportunities for process resource reduction without diverting critical engineering personnel from their core responsibilities.

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+ Transient Analysis Of Silicon Carbide Mosfet Switches
  K. Lawson; S. B. Bayne
Abstract:  This research was conducted to determine the transient performance of Silicon Carbide MOSFET devices. The device under test for these results is a CREE CMF20120D D-MOSFET rated for a blocking voltage of 1200 V and a forward conduction current of 20 A. The first test involves testing the limit of voltage rise time, or the dV/dt of these devices to determine when the device turns itself on. The second test studies the effects of large current pulses, 10x the rated current, on these devices to determine how well these devices are able to handle over current situations. For both of these tests a test bed had to be designed and built.

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+ Vehicle Development Process For Ecocar: The Next Challenge Competition
  K. Patil; T. Maxwell; S. Bayne; R. Gale
Abstract:  Present work investigates development of the vehicle design in the Texas Tech University EcoCAR program with industry standard vehicle development process (VDP). The three different architectures considered are fuel cell, GM two-mode hybrid and belt alternator/starter system (BAS+). The design process started from the architecture selection with the use of PSAT software. Based on results, best choice of vehicle architecture among the three considered is two-mode hybrid. With Matlab/Simulink environment vehicle model is developed. The plant model and controller model is tested with software-in-loop (SIL) and hardware-in-loop (HIL) simulations. The testing of this stage is done with NI PXI and dSPACE MicroAutoBox.

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Publication Year:  2009
+ A 15 Ka Linear Transformer Driver
  D. Matia; H. Krompholz; M. Giesselmann; A. Neuber; M. Kristiansen
Abstract:  The design of a 15 kA linear transformer driver (LTD) is presented. The specific goal of this LTD was improved energy density over the 500 J compact Marx generator previously designed and built at Texas Tech's Pulsed Power lab. The design of an individual 50 joule, 30 kV stage is discussed. For successful operation of the LTD, multiple spark gaps have to be fired with low jitter. Possible approaches for the design of a compact, low jitter triggering circuit will be presented as well.

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+ A Compact 5Kv Battery-Capacitor Seed Source With Rapid Capacitor Charger
  Holt, SL; Dickens, JC; McKinney, JL; Kristiansen, M
Abstract:  Many pulsed power applications have demanding system requirements. Power systems for these applications are expected to provide high energy, high pulsed power and long standby times without recharge, all in a very compact package. The different properties of batteries and capacitors make them most suitable for different uses. When selecting a prime power source for compact pulsed power systems a hybrid system often provides the optimal solution, utilizing a battery for prime energy storage during standby and a capacitor for intermediate energy storage before and between operations. This system takes advantage of the best characteristics of both sources to fulfill the system requirements. The design and testing of such a compact system is discussed. The system utilizes a solid-state converter to charge a 50 mu F polypropylene capacitor to 5 kV in under 500 ms from lithium-ion polymer (LiPo) batteries. Battery selection and testing is also covered. The battery and charger assembly occupies 1.25 L while the capacitor occupies an additional 1.4 L.
+ Design Of A Compact Power Conditioning Unit For Use With An Explosively Driven High Power Microwave System
  Korn, J; Neuber, A; Young, A; Davis, C; Kristiansen, M; Altgilbers, LL
Abstract:  The generation of high power microwaves using explosively driven pulsed power is of particular interest to the defense community. The high energy density of explosives provides the opportunity to design pulsed power systems which occupy significantly less volume, yet provide the same output power, as traditional methods of High Power Microwave (HPM) production. Utilizing a Flux Compression Generator (FCG) as explosive driver necessitates introducing an intermediate Power Conditioning System (PCS) that addresses the typical impedance mismatch between FCG and HPM source. The presented PCS is composed of an energy storage inductor, an opening fuse switch and a self-break peaking gap all of which needed to fit within an envelope of 15 cm diameter. Currents in the tens of kilo-amperes and voltages in the hundreds of kilo-volts have to be handled by the PCS. The design of the system, which takes up less than 11 liters of volume, as well its performance into a 20 Omega resistive load (used to approximate the operating impedance of certain HPM sources) is presented. Approximately 6 GW of electrical peak power was delivered to the load.
+ Development Of A 40-Stage Distributed Energy Railgun
  R. Karhi; M. Giesselmann; D. Wetz; J. Diehl
Abstract:  The development process pertaining to the design, fabrication, and testing of a 40-stage free-running arc synchronous distributed energy railgun is presented. Investigation of this type of system will determine the effectiveness of a distributed energy scheme to suppress the plasma restrike phenomenon and increase plasma armature railgun performance. Determined by a computer simulation, the proposed system will have a 1.0 cm ? 1.0 cm square bore cross section and a stage length of 15.24 cm producing a total rail length of 6 meters for 40 stages. A free-arc is utilized to relieve the financial burden of a large stored energy facility. A velocity of 8 km/s is desired to emulate conditions during a high altitude microsatellite launch. To achieve this velocity, pulsed power in conjunction with a low pressure (~ 10 Torr) air environment is required. The pulsed power supplies 15 kJ of energy to provide an armature current (~ 50 kA) for 1 millisecond. A real-time feedback control system will accurately release the stage energy upon arc arrival. Experimental data collected from a 7-stage prototype distributed system is discussed which will mimic the design and operation of the first 7 stages associated with the 40-stage railgun. The copper rail length is 1.2 m long with a 1 cm ? 1 cm square bore cross section and a 15.24 cm stage length. Each distributed energy stage contains a 750 ?F capacitor bank, a thyristor with an anti-parallel diode, and a driver board for triggering. The armature is formed using a plasma injector that is powered by a 40 kV Marx generator. Diagnostics for this examination include rail B-dot probes as well as independent Rogowski coils for each stage. Data collected from the rail B-dot probes will be used to measure the armature position and velocity as a function of time. There is no target velocity for this prototype; repeatable energy module operation, accurate stage triggering, and arc propagation toward the muzzle are the main areas focus. Outcomes of these initial experimental results will aid the development of the 40-stage system.

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+ Electrical Conduction In Select Polymers Under Shock Loading
  Lynn, C; Neuber, A; Krile, J; Dickens, J; Kristiansen, M
Abstract:  It is known that polymers become conductive under shock loading, which can be critical to the operation of explosive driven high current/voltage devices. Hence, the propensity of several select polymers to conduct under shock loading was investigated. Four polymers, Nylon, Teflon, Polypropylene, and High Density Polyethylene, were tested under shock pressures up to similar to 22 GPa. Shock waves were generated with high explosives, and CTH, a hydrodynamic code developed at Sandia National Laboratories, was utilized to calculate pressure and temporal resolution of the shock waves. Time of arrival measurements of the shock waves were taken to correlate the hydrodynamic calculations with experimental results. A notable delay between shock front arrival and the onset of conduction is exhibited by each polymer. The delay tends to decrease with increasing pressure down to approximately 500 ns for HDPE at similar to 22 GPa under electric field strength of similar to 6.3 kV/cm. The data shows that some polymers exhibit more delay than others, thereby indicating better insulating properties under shock loading. Additionally, experiments revealed that the polymers conducted for a finite time on the microsecond time scale before recovering back to an insulating state. This recovery from a shock wave induced conducting state back to insulating state was investigated for a possible opening switch application
+ Energy Deposition Assessment And Electromagnetic Evaluation Of Electroexplosive Devices In A Pulsed Power Environment
  Parson, J; Dickens, J; Walter, J; Neuber, A
Abstract:  This paper assesses critical activation limits of electroexplosive devices (EED), such as blasting caps, which have recently found more usage in pulsed power environments with high EMI background. These devices, EEDs, can be very sensitive to low levels of energy (7-8 mJ) which make them dangerous to unintended radiation produced by compact pulsed generators. Safe operation and use of these devices are paramount when in use near devices that produce pulsed electromagnetic interference. The scope of this paper is to provide an evaluation of activation characteristics for EEDs that include energy sensitivity tests, thermodynamic modeling, and electromagnetic compatibility from pulsed electromagnetic interference. Two methods of energy deposition into the bridgewire of the EED are used in the sensitivity tests. These methods include single and periodic pulses of current that represent the adiabatic and non-adiabatic heating of the bridgewire. The heating of the bridgewire is modeled by a solution to the heat equation using COMSOL (TM) with physical geometries of the EED provided by the manufacturer.
+ High Electric Field Packaging Of Silicon Carbide Photoconductive Switches
  Hettler, C; James, C; Dickens, J
Abstract:  Photoconductive semiconductor switches (PCSS) made from semi-insulating (SI) silicon carbide (SiC) are promising candidates for high frequency, high voltage, and low jitter switching. However, existing switches fail at electric fields considerably lower than the intrinsic dielectric strength of SiC (3 MV/cm) because of the field enhancements near the electrode-semiconductor interfaces. Various geometries were identified which could reduce the electric field near the contact regions. The switches were simulated with various parameters and compared. In all cases, it was determined that a high dielectric constant (high-k) encapsulant is a crucial requirement that reduces high fields within the bulk material while inhibiting surface flashover. Assorted high-k encapsulants were evaluated and a portion was subsequently tested in the lab. The observed dielectric strength and relative permittivity of the encapsulants are presented. Pseudo switches, employing sapphire substrates, were constructed and biased to electrical breakdown. The dielectric strength of the interface between the semiconductor and the encapsulant was tested and improvements were discussed.
+ High Voltage Photoconductive Switches Using Semi-Insulating, Vanadium Doped 6H-Sic
  James, C; Hettler, C; Dickens, J
Abstract:  SiC manufacturers are continually improving the purity of their wafers, however, interband impurities, while detrimental in many applications, can be useful in the operation of photoconductive switches. Compact, high-voltage photoconductive switches were fabricated using c-plane; vanadium doped 6H-SiC obtained from II-VI, Inc. This material incorporates a large amount of interband impurities that are compensated by the vanadium amphoteric, but at present is only available as c-plane wafers. In order to avoid micropipe defects, lateral switches were fabricated to allow validation of material simulations. Low resistivity contacts were formed on the semi-insulating material and a high-voltage encapsulant increases the surface flashover potential of the switch. Material characteristics were determined and switch parameters were simulated with comparisons made to experimental data.
+ High-Power Compact Capacitor Charger
  M. G. Giesselmann; T. T. Vollmer
Abstract:  We are reporting on a new design for a compact high power Capacitor charger with a power output that far exceeds the peak power of previously reported designs. For this purpose we are evaluating parallel modular designs with separate inverters, transformers, & rectifiers and compare them with designs with a larger module size. For larger power implementations with a single inverter, transformer, & rectifier, the main challenge is the design of the inverter using parallel connected IGBT transistors and their current sharing. We are demonstrating an implementation were we are combining 2 H-Bridge inverters in parallel to feed the primary of a 100 kVA compact step-up transformer. Each H-Bridge is using current mode control to enforce current sharing. The oscillators in the current mode control IC's for each H-Bridge are synchronized for this parallel mode of operation. This topology could be expanded to more H-Bridges. In order to reduce the high-frequency impedance and the windings losses of the step-up transformer, litz wire is used for both the primary winding and the secondary windings.

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+ Integration Of A Self-Contained Compact Seed Source And Trigger Set For Flux Compression Generators
  M. A. Elsayed; A. A. Neuber; M. Kristiansen; A. Stults; L. Altgilbers
Abstract:  Two integral components that accompany an FCG in an explosively driven system is the prime power source and the trigger set. The objective of the prime power source or seed source is to provide the initial seed current/energy into the primary stage of an FCG. Another integral component in an FCG based pulsed power system is the trigger set. The trigger set is used to detonate an exploding bridge wire (EBW) which triggers the high explosives (HE's) in an FCG. This paper will discuss a recent design of a stand-alone apparatus that implements a self-contained (battery powered with full charge time less than 40 sec), single-use Compact Seed Source (CSS) using solid state components for the switching scheme along with a single-use Compact Trigger Set (CTS) that also implements a similar switching technique. The CSS and CTS stand-alone apparatus developed is a system (0.005-m3 volume and weighing 3.9 kg) capable of delivering over 360-J (~12 kA) into a 5.20-¿H FCG load and approximately 2-mJ (~600 A) into the EBW. Both the CSS and CTS have trigger energies of micro-Joules at the TTL triggering level.

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+ Low Jitter Triggered Spark Gap With High Pressure Gas Mixtures And Kr85
  Y. Chen; J. C. Dickens; J. W. Walter; M. Kristiansen
Abstract:  Summary form only given. A recent research effort at Texas Tech University on impulse antenna phased arrays has necessitated the need to develop a reliable high voltage, high repetition rate switch that will operate with ultra low jitter. An ideal jitter of a small fraction of the risetime is required to accurately synchronize the array to steer and preserve the risetime of the radiated pulse. A 50 Omega, 1 nF pulse forming line is charged to 50 kV and provides the low inductance voltage source to test the different gases. Triggering is provided by a solid state opening switch voltage source that supplies ~80 kV, 10 ns risetime pulses at a rep rate up to 100 Hz in burst mode. A hermetically sealed spark gap with a Kel-F lining is used to house the switch and high pressure gas. Previously, the system was successfully tested with 50 kV, 100 Hz switch operations. Gases tested include, dry air, H2, N2, and SF6, as well as H2-N2, and N2-SF6 gas mixtures. A discussion on switch operation time and switch gas temperature vs. jitter will be included in this paper. This paper will also discuss in detail the effects on switch jitter when different concentrations of Kr85 gas are introduced.

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+ Optimizing Power Conditioning Components For A Flux Compression Generator Using A Non-Explosive Testing System
  Davis, C; Neuber, A; Young, A; Walter, J; Dickens, J; Kristiansen, M
Abstract:  This paper discusses a non-explosive pulsed power device used to reproduce the output waveforms of a Flux Compression Generator (FCG) driving a High Power Microwave (HPM) source. This system optimizes the power conditioning components of a HPM source while reducing the time and resources inherent to explosively driven FCG schemes. An energy storage inductor, fuse opening switch, and a peaking gap make up the power conditioning system. This system couples large voltage pulses (similar to 300 kV), suited for HPM sources, to the load by disrupting the energy storage inductor current (similar to 40 kA). This paper will show that an optimal fuse length was experimentally searched for by varying the calculated fuse wire base length by 5, 10, and 15%. Various geometric fuse designs were examined to achieve a 45% reduction in the physical fuse length at constant wire length with acceptable performance losses. This paper will also show that the distance between the electrodes of a peaking gap can be optimized to more efficiently switch in the load. Finally results will be shown that depict the amount of microwave power produced by a vircator before fuse and peaking gap optimization.
+ Performance Of A Compact Triode Vircator And Marx Generator System
  Walter, J; Dickens, J; Kristiansen, M
Abstract:  Vircator high power microwave sources are simple, robust, and require no external magnetic field, making them desirable for use in practical compact high power microwave systems. A vircator can be driven directly from the output of a low-impedance Marx generator, eliminating the need for bulky intermediate energy storage components. A compact high power microwave system has been constructed and tested at Texas Tech University utilizing a triode geometry vircator and a compact Marx Generator. The size and performance of this system is compared to a similar system previously developed at Texas Tech. The current triode vircator is housed within a six inch diameter tube which is eleven inches in length. The Marx is contained in an oil tank that is 36 inches long x 12 inches wide x 18 inches tall. Diode voltage and current, and radiated microwave waveforms are presented.
+ Prediction Of Compact Explosively-Driven Ferroelectric Generator Performance
  Bolyard, D; Neuber, A; Krile, J; Dickens, J; Kristiansen, M
Abstract:  Explosively-driven ferroelectric generators are attractive as potential prime energy sources for one-time use pulsed power systems. While the output voltages of small ferroelectric discs have been shown to be on the order of the theoretical maximum values, scaling the ferroelectric to larger thicknesses has proven less successful. The primary limiting factor is how much of the ferroelectric material is compressed simultaneously. This is difficult to control for thicker ferroelectric discs or stacks of discs due to pressure pulse attenuation in the material and rarefaction waves shortening the pressure pulse. A hydrodynamic code system is utilized to calculate the temporally and spatially resolved pressure. The calculated pressure values are converted into voltage produced by the ferroelectric through an algorithm based on an empirical polarization-pressure hysteresis curve. The validity of the algorithm has been verified for PZT EC-64 with experimental data from a flyer-plate experiment reported in literature and our own experiments with the shock wave from the explosives more directly applied to the ferroelectric. Both calculations and experiments produced normalized output voltages, ranging from 1.4 to 3.4 kV/mm for 2.54 cm diameter discs. We will discuss how this pressure to voltage algorithm along with pressure simulations aided in the scaling of the amount of ferroelectric material in a generator, as well as in the design of new driver elements with the goal to increase the peak output voltage of a generator while keeping the generator compact. The calculated voltage output results are compared with experimental data of explosively-driven ferroelectric generators.
+ Stand-Alone, Fcg-Driven High Power Microwave System
  Young, A; Neuber, A; Elsayed, M; Walter, J; Dickens, J; Kristiansen, M; Altgilbers, LL
Abstract:  An explosively driven High Power Microwave (RPM) source has been developed that is based on the use of a Flux Compression Generator (FCG) as the primary driver. Four main components comprise the HPM system, and include a capacitor-based seed energy source, a dual-staged FCG, a power conditioning unit and an RPM diode (reflex-triode vircator). Volume constraints dictate that the entire system must fit within a tube having a 15 cm diameter, and a length no longer than 1.5 m. Additional design restrictions call for the entire system to be stand-alone (free from any external power sources). Presented here are the details of RPM system, with a description of each subcomponent and its role in the generation of RPM. Waveforms will be shown which illustrate the development of power as it commutates through each stage of the system, as well as power radiated from the diode. Analysis and comparisons will be offered that will demonstrate the advantages of an explosively driven HPM system over more conventional pulsed power devices.
+ Vuv Emission From Dielectric Surface Flashover At Atmospheric Pressure
  Rogers, G; Neuber, A; Laity, G; Dickens, J; Frank, K; Schramm, T
Abstract:  Spectroscopic measurements in the vacuum ultraviolet (VUV) regime are difficult to make due to extremely large absorption of VUV radiation in most materials. This paper describes an experimental setup designed for studying the optical emission during pulsed surface flashover for the wavelength range between 115 nm to 180 nm at atmospheric pressures with a focus on the scheme used to excite the spark gap. The surface flashover of interest occurred on an MgF2 window (front side of window in air, backside in vacuum) imaged onto the entrance slit of a 1 m vacuum spectrograph. Emission spectra were recorded with an Andor DH740 series ICCD camera. All data was taken at atmospheric pressure with a flashover spark length of about 8 mm created by a pulser designed for a 500 ns pulse, max 50 kV output. The centerpiece of this pulser is the CCSTA14N40 thyristor by Solidtron / Silicon Power which features a rate of change current of maximum 30 kA/mu s and a hold-off voltage of up to 4 kV. A pulse transformer with Metglas (R) core was used to elevate the voltage to 50 kV with a rise time of 180 ns and a peak current of 500 A. The pulser was designed for a repetition rate of 10 Hz and is triggered by TTL pulses. Discussed in this paper, along with the measured spectra and their relation to the physics of surface flashover at atmospheric pressure, will be the design of the pulser.
Publication Year:  2008
+ A 50 Kv, 100 Hz Low Jitter Triggered Spark Gap With High Pressure Gas Mixtures
  Y. Chen; J. J. Mankowski; J. C. Dickens; J. Walter; M. Kristiansen
Abstract:  Recent research efforts at Texas Tech University on impulse antenna phased array has necessitated the need to develop a reliable high voltage, high repetition rate switch that will operate with ultra low jitter. An ideal jitter of a small fraction of the risetime is required to accurately synchronize the array to steer and preserve the risetime of the radiated pulse. In (Y. Chen et al., 2007), we showed the initial test system with sub-ns results for operations in different gases and gas mixtures. This paper presents the impact gases and gas mixtures have on switch performance which includes recovery rate and in particular jitter. A 50 Omega, 1 nF pulse forming line is charged to 50 kV and provides the low inductance voltage source to test the different gases. Triggering is provided by a solid state opening switch voltage source that supplies ~150 kV, 10 ns risetime pulses at a rep rate up to 100 Hz in burst mode. A hermetically sealed spark gap with a Kel-F lining is used to house the switch and high pressure gas. This paper discusses in detail 50 k, 100 Hz switch operations with different gases. Gases tested include, dry Air, H2, N2, and SF6, as well as H2-N2, and N2-SF6 gas mixtures. Switch jitter as a result of triggering conditions is discussed, also including a comprehensive evaluation of jitter as a function of formative delay in the various gases.

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+ A Compact, Self-Contained High Power Microwave Source Based On A Reflex-Triode Vircator And Explosively Driven Pulsed Power
  Young, A; Holt, T; Elsayed, M; Walter, J; Dickens, J; Neuber, A; Kristiansen, M; Altgilbers, LL; Stults, AH
Abstract:  Single-shot High Power Microwave (HPM) systems are of particular interest in the defense industry for applications such as electronic warfare. Virtual Cathode Oscillators (vircators) are manufactured from relatively simple and inexpensive components, which make them ideal candidates in single-shot systems. The Flux Compression Generator (FCG) is an attractive driver for these systems due to its potential for high energy amplification and inherent single-shot nature. A self-contained (battery operated prime power), compact (0.038 m(3)), FCG-based power delivery system has been developed that is capable of delivering gigawatts of power to a vircator. Experiments were conducted with the delivery system connected to a resistive dummy load and then to a reflex-triode vircator. In order to optimize the performance of the vircator when driven by the power delivery system, a second experimental setup was constructed using a Marx-generator based system operating at similar voltages and rise-times. Performance measures of the delivery system when discharged into a resistive load will be presented, as well as vircator output power levels and waveforms from both experimental setups.
+ Analysis Of Distributed Energy Railguns To Suppress Secondary Arc Formation
  R. W. Karhi; J. J. Mankowski; M. Kristiansen
Abstract:  An investigation into arc splitting at distributed energy feed locations is presented. Distributed energy scheme experiments conducted at Texas Tech University reveal secondary arc formation by arc splitting at distributed current feeds. At these locations, dynamic magnetic pressure regions are believed to perturb the plasma and lead to its division into two separate current carrying bodies. Continuing research into this hypothesis and viable methods of prevention are discussed. A two stage distributed energy railgun is utilized for this analysis. Diagnostics including armature B-dots and a photodiode array facilitate an understanding of the plasma dynamics in the complex multi-stage railgun environment. The length of the free- running plasma arc allegedly is believed to be a contributing parameter into the arc splitting phenomenon. These luminosity data collected from the photodiodes provides an arc length measurement of the light emitting particles within the plasma body. This length is observed to expand and contract in accordance with the corresponding magnetic pressure present within the railgun bore.

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+ Analysis Of Mesoband Single Element Pulsed Ring-Down Antennas For Implementation In Phased Array Systems
  Belt, D; Mankowski, J; Walter, J; Dickens, J; Kristiansen, M
Abstract:  In recent years, the pulsed ring-down antenna has become of great interest due to its compact size and high power on target potential. Since these systems are fairly new in study, it is often difficult to predict the overall performance without experimental evaluation. A pulsed ring-down antenna operates by charging the single element antenna with a high potential source and then dosing a switch to develop transient wave reflections on the antenna, typical CW case analysis does not apply. For this reason, we have constructed a simulation model that allows us to predict the transient behavior of the structure. By utilizing the Comsol RF module transient analysis functions, we are able to characterize various parameters of different antennas, beginning with a dipole pulsed ring-down antenna operating around the 100 MHz range. After examining the simulated results against the experimental results for accuracy, we then moved to more complicated mesoband antenna structures. The simulation model developed within the COMSOL RF module allows us to examine various influential factors such as material losses, transient switching effects, structure capacitance, switch capacitance, and initial charging losses. With this, we are able to examine methods to improve the results in the far field such as capacitive spark gap loading and other capacitive storage methods. Utilizing the pulsed ring-down antenna model, we are able to give a better characterization of mesoband pulsed ring-down structures for implementation into a specific or multi-purpose phased array system.
+ Capacitor Evaluation For Compact Hv Pulse Generation
  Matthews, EJ; Neuber, AA; Kristiansen, M
Abstract:  The size of compact pulsed power generators capable of producing pulses with similar to 100 ns duration at Gigawatt power levels is primarily determined by the specific energy density of the utilized energy storage medium Capacitors capable of delivering large pulsed currents at several 10 kV voltage levels have been most frequently used as the energy storage medium for portable pulse generators. To increase the specific energy density of the pulsed power generator, the capacitors are often voltage overstressed at the cost of capacitor life. However, rapid charging (milliseconds) of the capacitor immediately followed by discharging alleviates somewhat of the lifetime problem. For repetitive operation of the pulsed power generator, the charging/discharging energy loss is the more important parameter. The energy, W-C, needed to charge a capacitor to a set voltage is measured along with the energy released, W-R, by the capacitor under conditions corresponding to a compact Marx generator operating with similar to 10 Hz rep-rate into a similar to 20 Ohm load. For the tested capacitors with Mica as dielectric, the capacitor efficiency, eta, i.e. the ratio between W-R and W-C, is roughly equal to 97% and largely independent of the charging time. Also tested ceramic capacitors revealed an efficiency of similar to 90% for fast charging and an efficiency of similar to 94% for slower charging (from similar to 2 to 35 mu s time constant).
+ Compact Hv-Capacitor Charger
  M. Giesselmann; T. Vollmer; M. Lara; J. Mayes
Abstract:  We are reporting on a compact high power charger which is integrated into compact Marx generators for rep. rated high power microwave generators and other pulsed power applications. The charger uses rectified AC mains input voltages of 120 V single phase or 208 V three phase and produces output voltages of up to ten's of kV with HV output power levels of 10 kW. The rep. rate capability is up to 100 Hz. Major advancements over previous designs are current mode control of the main inverter and improved voltage feedback control.

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+ Compact Hv-Dc Power Supply
  M. Giesselmann; T. Vollmer; R. Edwards; T. Roettger; M. Walavalkar
Abstract:  We are reporting on a compact high voltage (HV) power supply that can be used in the mobile or airborne generation of high power microwave generators. The charger uses rectified AC mains input voltages of 480 V three phase and produces output voltages of more than 55 kV with HV output power levels of 100's of kW continuously. Major advancements over a previous design are the design of the secondary winding of the HV nano-crystalline transformer, the control of the primary inverter and the thermal management and diagnostic of the HV-DC rectifier.

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+ Compact Silicon Carbide Switch For High Voltage Operation
  James, C; Hettler, C; Dickens, J; Neuber, A
Abstract:  Vanadium compensated, 6H silicon carbide (SiC) is investigated as a compact, high-power, linear-mode photoconductive semiconductor switch (PCSS) material. SiC is an attractive material due to its high resistivity, high electrical breakdown strength, and long recombination times compared to other photoconductive materials. The PCSS is designed for fast-rise time, low-jitter (sub-nanosecond) operation in a matched 50 Omega test bed. Ohmic contacts were applied by physical vapor deposition and initial tests utilized an external Nd:YAG laser trigger source. Analysis of the optical properties of Va-compensated SiC and of switch conduction resistance are presented and performance of contact material is discussed.
+ Energy Deposition And Electromagnetic Compatibility Assessment Of Electroexplosive Devices
  Parson, J; Dickens, J; Walter, J; Neuber, A
Abstract:  This paper assesses the critical activation energy required to set off electroexplosive devices (EED) at constant joule heating and rates of joule heating. Safe operation and use of these devices are of great concern in and around pulsed electromagnetic interference. Sensitivity characterization of EEDs include firing sensitivity plots, thermodynamic modeling and electromagnetic interference. Activation energy evaluation of single and periodic rectangular pulses are included to represent adiabatic and non-adiabatic bridge wire heating of the EED. The scope of this paper is to provide a short overview of sensitivity, thermodynamic, and electromagnetic compatibility of EEDs. The results provide crucial information in evaluating energy induced by pulsed electromagnetic fields of compact pulse generators.
+ High-Current Compact Fcg Seed Source Implementing Solid State Switching
  Elsayed, M; Holt, T; Young, A; Neuber, A; Dickens, J; Kristiansen, M; Altgilbers, LL; Stults, AH
Abstract:  Flux Compression Generators (FCGs) are some of the most attractive sources of single-use compact pulsed power available today due to their high energy density output and mobility. Driving FCGs requires some seed energy, which is typically provided by applying a high seed current, usually in the kilo-Ampere range for mid-sized helical FCGs. This initial current is supplied by a high-current seed source that is capable of driving an inductive load. High-current seed sources. have typically been comprised of discharging large capacitors using spark-gaps and over-voltage triggering mechanisms to provide the prime power for FCGs. This paper will discuss a recent design of a self-contained (battery powered with full charge time less than 35 sec), single-use Compact Seed Source (CSS) using solid state components for the switching scheme developed at the Center for Pulsed Power and Power Electronics at Texas Tech University. The CSS developed is a system (0.007-m(3) volume and weighing 13 lbs) capable of delivering over 250-J (similar to 10 kA) into a 6-mu H load with a trigger energy of micro-Joules at the TTL triggering level. The newly designed solid-state switching scheme of the CSS incorporates off-the-shelf high-voltage semiconductor components that minimize system cost and size as necessary for a single-use application. An in-depth and detailed evaluation of the CSS is presented primarily focusing on the switching mechanics and experimental characterization of the solid state components used in the system.
+ Jitter And Recovery Rate Of A 50 Kv, 100 Hz Triggered Spark Gap With High Pressure Gas Mixtures
  Yeong-Jer Chen; J. J. Mankowski; J. W. Walter; J. C. Dickens
Abstract:  Summary form only given.Recent attention to impulse antenna phased array has necessitated the need to develop a reliable high voltage, high repetition rate switch that will operate with ultra low jitter. An ideal jitter of a small fraction of the rise time is required to accurately synchronize the array to steer and preserve the rise time of the radiated pulse. This paper presents the impact gases and gas mixtures have on switch performance which includes recovery rate and in particular, jitter. A 50 Omega, 1 nF pulse forming line is charged to 50 kV and provides the low inductance voltage source. Triggering is provided by an SOS voltage source that supplies >100 kV, 10 ns rise-time pulses at a rep rate up to 1 kHz in burst mode. A hermetically sealed spark gap with a Kel-F lining is used to house the switch and high pressure gas. The system includes a gas mixing chamber that can mix various gases up to 2000 psi. Gases tested include dry air, H2, N2, and SF6. Initial testing with 30 kV, 10 Hz switch operations have shown reliable sub-ns jitter times with pure gases including dry air, H2, N2, and with H2-N2, and N2-SF6 gas mixtures. The system was then modified for 50 kV, 100 Hz operations with no recovery issues. Jitter data for pure gases, H2-N2, N2-SF6, and various Kr85 gas mixtures at the 50 kV, 100 Hz operation is also documented and compared in this paper.

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+ Opening Switch Utilizing Stress Induced Conduction In Polymethylmethacrylate
  Lynn, C; Krile, J; Neuber, A; Dickens, J
Abstract:  It is known that polymethylmethacrylate, PNUqA, becomes conductive under shock loading. To develop an opening switch utilizing shock induced conduction, the reversibility of this process must be studied. It is suggested in literature that changes in electrical properties begin at pressures as low a similar to 2 GPa. Applying the minimum pressure necessary for conduction is desirable in order to maximize the reversibility by limiting compression heating of the material. CTH, a hydrodynamic code written at Sandia National Laboratory, was used to design various drivers that deliver pressures in the range of similar to 2 GPa to 4 GPa to the PMMA. By utilizing the switch to trigger an RC discharge, the resistance and on-time of the switch was characterized. Experiments have shown conduction durations on the order of similar to 4 mu s. The switch was then placed into a capacitive driven inductive energy storage circuit, IES, to determine the polymer's ability to recover. This paper will present experimental data, CTH simulation results, and discuss the attained switching characteristics under varying shock pressure profiles.
+ Particle Simulation Of Ultrafast Closing Switch At Sub-Atmospheric Pressures
  J. Chaparro; H. Krompholz; A. Neuber; L. Hatfield
Abstract:  Previous research at Texas Tech University has been conducted on the physics governing highly over-voltaged gas breakdown resulting from ultrafast applied voltage pulses with risetimes less than 200 ps and durations less than 400 ps. Experimental results have shown that the breakdown characteristics of such events significantly differ from those observed in standard gas breakdown and a complete understanding of the physics behind ultrafast discharges is far from being clear. As a companion to experimental work, a numerical model is an attractive means of discerning more about the underlying physics behind such events. In this paper, a relativistic, Particle in cell model utilizing Monte-Carlo calculations is discussed as a way to directly simulate the experimental conditions, with similar geometry, background gas, and pulse characteristics. Diagnostic output from the simulation includes space-charge development over time, field and particle energy distributions, and particle number growth rates and spatial distributions. An overview of the structure and formulation behind the simulation code is given followed by a comparison of output data to experimental results. Specific points of interest for comparison include formative and statistical delay times, examination of inhomogeneous ionization regions in the discharge, and the behavior of high-energy particles in the runaway state.

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+ Scaling And Improvement Of Compact Explosively-Driven Ferroelectric Generators
  Bolyard, D; Neuber, A; Krile, J; Walter, J; Dickens, J; Kristiansen, M
Abstract:  Explosively-driven ferroelectric generators are capable of producing single-shot voltage pulses of more than 100 W, while requiring no seed electrical source, being very compact, and shelf stable. Problems with ferroelectric generators are the low energy output, high dielectric constant of the ferroelectric material, low surface flashover voltage, inconsistent ferroelectric material quality, and uneven or excessive shockwave compression. Initial generator voltage waveforms show that breakdown occurred towards the end of the generator operation time. Several designs and methods have been tested and implemented to prevent surface flashover with varying results. The ferroelectric discs used for the generators were 0.4 inch thick, 1 inch diameter EC-64 PZT ceramic discs. Several six-disc generators were built and tested with resulting open-circuit voltage pulses of 80-140 kV with a FWHM of 2-4 mu s. Further improvements to the generators have been designed to prevent surface flashover, improve the explosive driver element and propagating shockwave, as well as increasing the number of discs per generator. Measured output waveforms into varying loads including direct driven antennas will be shown and discussed.
+ Shock Wave Simulation Of Ferrite-Filled Coaxial Nonlinear Transmission Lines
  Sullivan, W; Dickens, J; Kristiansen, M
Abstract:  Ferrite-filled coaxial shock lines have recently been used to significantly decrease the rise time of a high voltage pulse. This decrease can be enhanced by initially axially biasing the ferrite material with an applied external magnetic field, allowing for a faster transition from the unsaturated to the saturated state. The simulation of the ferrite material's operation, including saturation, is discussed as well as the simulation of coaxial nonlinear transmission lines. The project explores the rise time changes with variations of magnetic bias, ferrite geometry, input signal characteristics, and transmission line characteristics. Simulated waveforms are discussed for a nickel-zinc ferrite-filled coaxial line. The pulse steepening effect observed in electromagnetic shock lines occurs primarily because of an increase in phase velocity for points higher on the waveform due to the saturation of the ferrite material [1]. An incident pulse of high enough amplitude will drive the ferrite material into saturation, decreasing the relative permeability to one. This saturation front propagates through the ferrite material in the direction of the incident wave until the entire material is saturated, producing a sub-nanosecond rise time pulse. The shock line is designed for a saturated impedance of 50 Ohms to couple easily into existing systems. Pulsed operation of up to low kilohertz repetition is desired and being explored. Applications of electromagnetic shock lines include laser triggering and ultra-wideband radar generation, as well as others.
+ Short Rise Time High Power Microwave Induced Surface Flashover At Atmospheric Pressures
  J. Foster; G. Edmiston; J. Krile; H. Krompholz; A. Neuber
Abstract:  High power microwave transmission is ultimately limited by window flashover at the vacuum-air dielectric boundary. While surface flashover in the presence of a vacuum has been studied in some detail, the mechanisms associated with flashover in an atmospheric environment need further investigation. For an aircraft based high power microwave system, atmospheric pressures ranging from 760 torr (sea level) to 90 torr (50,000 ft.) are of principal concern. The experimental setup uses a 2.85 GHz, 3 mus microwave pulse with a 10 to 90% rise time of approximately 600 ns from a magnetron capable of producing 5 MW. The slow rise time of the microwave pulse is sharply reduced by using a waveguide spark gap switch used for fast microwave reflection and a high power four port circulator [6]. This reflected pulse has a reduced rise time on the order of 50 ns. The shorter rise time produces a more ideal step waveform that can be more easily compared with theoretical perfect square pulse excitation. Past investigations showed that the delay time for breakdown in air increases with pressure as is expected from the right hand side of the Paschen curve as long as the electron collision frequency is much larger than the microwave frequency. Surface flashover experiments have produced similar results. At a pressure of 155 torr, for instance, the breakdown electric field strength is 6 kV/cm (power density 0.08 MW/cm2) and the overall delay time from HPM pulse application to reaching critical breakdown plasma density is 600 ns. An overview of the experimental setup is given along with a discussion of breakdown delay times as a function of pressure as well as an investigation of surface flashover in the presence of external UV (ultraviolet) illumination.

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+ Statistical And Formative Delay Times For Sub-Nanosecond Breakdown At Sub-Atmospheric Pressure
  J. Chaparro; L. Hatfield; H. Krompholz; A. Neuber
Abstract:  For subnanosecond switching, physical phenomena as well as basic breakdown data, such as delay times and breakdown voltages, are of interest. With a RADAN Pulser as source for voltage pulses with up to 180 kV amplitude and risetimes at a test gap of 180 ps, we investigate statistical and formative delays for argon and dry air at sub-atmospheric pressure, for gap widths of 1 and 11 mm. Formative times have minima between 50 and 200 torr, and range from 70 ps at 1.5 MV/cm to 200 ps at 50 kV/cm. For this range of electric fields, this dependence on pressure and applied field can be explained by the behavior of ionization coefficient and electron drift velocity for homogeneous discharges. For higher fields exhibiting a narrow ionization zone in cathode vicinity with pronounced electron runaway conditions, the experimental data agree with results of Monte-Carlo simulations. Statistical delays are about the same as formative delays at fields of 50 kV/cm, and are reduced with increasing field amplitude to less than 50 ps at 1.5 MV/cm. It appears that field emission is the major source for starting electrons, influencing the statistical delay time near the field emission threshold only.

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+ Window Flashover Initiation Under Pulsed Microwave Excitation
  Krile, J; Edmiston, G; Dickens, J; Krompholz, H; Neuber, A
Abstract:  Surface flashover development at the output window of high power microwave (HPM) systems presents a major limitation to the power densities and pulse lengths transmitted through these interfaces. As a result, developing a physical model accurate in predicting surface flashover initiation is of prime interest A Monte-Carlo type electron motion simulation has been developed to estimate the delay time from initial electron to flashover. Although this approach has shown reasonable agreement with experimental results, the process yielding the initial seed electron(s) was neglected in the model, primarily due to the lack of quantitative and qualitative information on seed electron production. For instance, computational efforts investigating seed electron production via collisional detachment from negative oxygen ions have shown that while effective at DC, the collisional detachment model cannot remain a likely contributor of electrons at high frequencies (> similar to 5 GHz). The key parameters impacting high power microwave surface flashover will be discussed and presented along with continued investigation into the statistics of possible seed electron sources, including trace contaminates present in the gas or on the dielectric surface.
Publication Year:  2007
+ A Synchronous Free-Running Arc Distributed Energy Railgun
  R. W. Karhi; J. J. Mankowski; J. C. Dickens
Abstract:  Summary form only given. Experimental results utilizing a distributed energy scheme and free-running arc are presented. Analysis and observations of the issues associated with distributed energy switching of a plasma armature in the railgun will be explored. The use of a free running arc allows experiments to emulate a plasma armature railgun at high speeds (> 5 km/s) without the requirement of a large amount of stored energy. Diagnostics for this examination include rail and plasma current probes as well as independent Rogowski coils for each stage. The distributed system is comprised of four stages spaced uniformly along the rail length. Each stage contains a high voltage capacitor, an inductor, a phase controlled SCR, and a driver board for triggering. The high voltage capacitors used are capable of storing 50 kJ, but are typically charged to store less than 20 kJ. Fiber optic lines are integrated into the system to prevent misfire in the noisy EMI environment. Optimal switch timing is predicted by a computer simulation and tested for accuracy. The assembled railgun is 2.4 m long with a 1.7 cm times 1.7 cm bore cross section. The rails are made of machined UNS C11000 ETP copper. G-10 insulation contains the current probes and separates the Aluminum 6061-T6 outer support structure from the rails. Alumina ceramic inserts are secured by the G-10 and function to reduce in-bore ablation. A PVC chamber encloses the railgun and allows experiments to be conducted within the desired 1-10 torr environment. A plasma source at the breech reliably supplies plasma for each experimental test. The plasma injector is powered by a Marx generator to supply a 40 kV voltage and pulse length of 10 s. The coaxial injector is comprised of a tungsten rod, ceramic insulator, and stainless steel outer casing. Numerous experimental tests were conducted to investigate the dynamics of plasma armatures within a distributed energy source railgun. Variations of switch timing, bore pressure, current amplitude, and current pulse length within each stage have been tested. This data is analyzed to determine the effectiveness of a distributed energy system to suppress the plasma restrike phenomenon and increase plasma armature railgun performance.

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+ An Asynchronous Free-Running Arc, Distributed Energy Railgun
  Karhi, R; Mankowski, J; Dickens, J; Kristiansen, M
Abstract:  Experimental results comparing a breech-fed scheme and a distributed energy scheme for a free-running arc are presented. Analysis and observations of the issues associated with distributed energy switching of a plasma armature in the railgun will be explored. The use of a free running arc allows experiments to emulate a plasma armature railgun at high speeds (>5km/s) without the requirement of a large amount of stored energy. Numerous experimental tests were conducted to investigate the dynamics of plasma armatures within a distributed energy source railgun. Variations of switch timing, bore pressure, current amplitude, and current pulse length within each stage have been tested. These data are analyzed to determine the effectiveness of a distributed energy system to suppress the plasma restrike phenomenon and increase plasma armature railgun performance(1).
+ Characterization Of A High Power Nanocrystalline Transformer
  R. C. Edwards; M. G. Giesselmann
Abstract:  Summary form only given. Nano-crystalline ferro-magnetic core material has very favorable magnetic properties for high frequency power applications. This paper investigates the properties of a nanocrystalline transformer with multiple secondary windings through experimental evaluation over a range of frequencies. Design considerations are addressed with special attention focused on scaling with respect to frequency, leakage inductance, and effective AC resistance of the windings. The data derived from the experimental evaluation yields scaling factors to help determine a transformer design for optimal power density.

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+ Compact Hv-Capcitor Charger
  M. G. Giesselmann; R. C. Edwards; M. Lara; J. Mayes
Abstract:  Summary form given only. We are reporting on a compact high power charger which is integrated into compact Marx Generators for rep. rated High Power Microwave generators and other Pulsed Power Applications. The charger uses rectified AC mains input voltages of 120V single Phase or 208V three phase and produces output voltages of up to 50 kV with HV output power levels of 10 kW. The rep. rate capability is up to 100 Hz. Major advancements over previous designs are current mode control of the main inverter, improved efficiency through advanced transformer design and improved feedback control.

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+ Continuum Models For Electrical Breakdown In Photoconductive Semiconductor Switches
  Hjalmarson, HP; Kambour, K; Myles, CW; Joshi, RP
Abstract:  In this paper, continuum models for electrical breakdown are described. These models are based on calculations of the carrier distribution function as a function of electric field and carrier density. In these continuum models, the impact ionization rate is approximated in the extremes of low and high carrier density. These continuum models are used for calculations of electrical breakdown in GaAs. In particular, these models are applied to the operation of photoconductive semiconductor switch (PCSS) devices. This comparison with data suggests that a new physics mechanism is required to explain the PCSS data, a new mechanism is hypothesized.
+ Development Of An Ultra-Compact Explosively Driven Magnetic Flux Compression Generator System
  Krile, J; Holt, S; Hemmert, D; Walter, J; Dickens, J; Altgilbers, L; Stults, A
Abstract:  Explosively driven magnetic flux compression generators (MFCG) are effective high current, compact, disposable pulsed power supplies [1]. A common type of MFCG in use is a helical generator, HFCG, because it can provide very high current gain in a compact form. Successful implementation of a HFCG as a pulsed power source requires several peripheral systems including a seed current source and a high current switching mechanism. Additionally, for driving higher impedance loads, a power conditioning system is required to convert the high current, low voltage HFCG output into a more suitable voltage. HEM Technologies' currently developed system utilizes an ultra compact, seed source previously developed by HEM Technologies [2]. An explosively driven closing switch provides both the switching action and acts as a delay generator to allow for the current rise in the HFCG. The output of the HFCG is conditioned via an exploding fuse wire and spark gap pair to convert the high current output to high voltage. HEM Technologies has performed extensive modification and testing of the end-to-end system. The current and energy conversion will be presented along with typical output voltages using different fusing techniques.
+ Effects Of Uv Illumination On Surface Flashover Under Pulsed Unipolar Excitation
  J. T. Krile; A. A. Neuber; H. G. Krompholz
Abstract:  Summary form only given. Dielectric surface flashover in an atmospheric environment is an important consideration in the design of insulating support structures for pulsed, high voltage applications. Only recently, increased effort has been invested in characterizing and quantifying the physical processes involved in surface flashover occurring at atmospheric conditions. We have previously shown qualitatively that UV illumination of the surface, either externally or possibly generated by the developing discharge itself, affects the distance between flashover path and surface for small gaps with a nonnegligible field component normal to surface. By studying the effects of UV illumination on the flashover behavior, information was gained about the underlying mechanisms of dielectric surface flashover. Utilizing a solid-state UV source with a much faster turn-off time than gas tubes along with the flashover testing apparatus' generally high temporal resolution enabled us to measure applied UV pulse, voltage, current and flashover self luminosity with high temporal precision. For all experiments, the dielectric flashover sample is placed inside an environmentally controlled chamber with a constant gas flow. Using advanced field simulations the electrode/dielectric geometry was designed to produce an optimized field shape for the testing of surface effects. Besides reducing the flashover delay times by up to 50%, the application of a 1 mW/cm2, 20 mus UV pulse, prior to the voltage pulse, forces the flashover discharge in nitrogen to "hug" the surface rather than develop a few millimeters away from the surface along the field lines. Increasing the time delay between UV and voltage pulse application, it was revealed that the impact of the UV pulse on the flashover path becomes weaker with a time constant, tau, of ~ 3.1 mus. That is, after roughly 10 mus (3 times tau), the flashover path develops as without any UV application at all. In addition to experimental data of dielectric surface flashover with varying degrees of UV illumination, we present a simple model that describes the observed behavior as well as a more advanced analysis utilizing a Monte Carlo type code for the electron collision dynamics.

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+ Electrical And Optical Measurements Of Explosively Driven Plasma Jets
  Walter, J; Dickens, J; Kristiansen, M
Abstract:  Electrical and optical measurements were performed on explosively driven plasma jets. The explosive devices are in the form of a conical shaped charge. The electrical diagnostic consisted of measuring the current passed through a jet Ab en it made a connection between two metal plates. An energy storage capacitor connected to the two plates was charged to between 500 V and 10 kV, and then discharged through the jet. Also, an ICCD camera was used to capture high-speed single frame pictures of the propagating jet. Several shots were fired with variations in the capacitor voltage, the plate geometry, and the jet material. Current waveforms and optical images are presented. All experiments were performed in the explosive and high power RF experimental facility at the Center for Pulsed Power and Power Electronics at Texas Tech University.
+ Electro-Explosive Fuse Optimization For Helical Flux Compression Generator Using A Non-Explosive Test Bed
  McCauley, D; Belt, D; Mankowski, J; Dickens, J; Neuber, A; Kristiansen, M
Abstract:  Helical Flux Compression Generators (HFCG) of 50 mm form factor have been shown to produce a maximum energy deposit of 3 kJ into a 3 mu H inductor from a seed current. A large dI/dt into a coupled load is possible when an electro-explosive fuse is used. Previous work with a non-optimized fuse has produced similar to 100 kV into a 15 Omega load which leads into a regime relevant for High Power Microwave (HPM) systems. It is expected that similar to 300 kV can be achieved with the present 2 stage HFCG driving an inductive storage system with an electro-exploding fuse. In order to optimize the electro-explosive fuse design, a non-explosive test bed, which closely simulates the 45 kA HFCG output, is used. To optimize the fuse, effects of fuse material, fuse length, and fuse shape will be examined as well as the effects of various quenching materials. Additionally, to maximize the output voltage and minimize the fuse recovery time, we are optimizing the length of the fuse wire. For shorter fuse lengths, we are optimizing fuse shape as well as fuse length to find the best fuse recovery time. By optimizing the individual parameters of an electro-explosive fuse, the fuse as a whole will be optimized to produce maximum output voltage when used with an HFCG.
+ Electro-Explosive Switches For Helical Flux Compression Generators
  Bell, D; Mankowski, J; Neuber, A; Dickens, J; Kristiansen, M
Abstract:  Helical Flux Compression Generators coupled with an inductive energy storage system have shown promising results as a driving source for High Power Microwave (HPM) loads. The output performance of the inductive energy storage system is contingent upon the opening switch scheme, usually an electro-explosive fuse. Our previous work involving fuse parameter characterization has established a baseline for potential fuse performance. By applying this fuse characterization model to an HFCG powered system, a non-optimized fuse has produced 60 kV into an HPM equivalent load with an HFCG output of 15 kA into a 3 mu H inductor. Utilization of a non-explosive HFCG test-bed has produced 36 kV into an HPM equivalent load with an output of 15 kA into a 1.3 mu H inductor. The use of a non-explosive HFCG test bed will allow the verification of scalability of the fuse parameter model and also allow testing of exotic fuse materials. Prior analysis of fuse parameters has been accomplished with various materials including Silver (Au), Copper (Cu), and Aluminum (Al), but particular interest resides in the use of Gold (Ag) fuse material. We will discuss the a-priori calculated baseline fuse design and compare the experimental results of the gold wire material with the silver wire material baseline design. With the results presented, an accurate Pspice model applicable to our 45 kA HFCG systems will be available and allow the development of accurate modeling for higher current systems.
+ Electromechanical Modeling Of Biomimmetic Actuation Behavior Of Electro-Active Paper (Eapap)
  Joshi, RP; Mbaye, F; Basappa, P; Sang-Dong, J
Abstract:  Measurements of bias-dependent deflections and strain in EAPap, as well as water absorption were carried out. Model simulations have also been performed to probe the role of the various internal mechanisms. Our simulation predictions yield good agreement with the measured data on EAPap deflections. The modeling suggests that internal ion content and its migration, water absorption leading to a non-uniform permittivity, random variations in the transverse piezoelectric-coupling coefficient d(31,i) and the modulus of elasticity, all collectively contribute to the EAPap deflection electro-physics.
+ Electro-Thermal Simulation Studies For Pulsed Voltage Failures In Microstructured Zno Varistors
  Zhao, G; Joshi, RP; Jalmarson, HP
Abstract:  Time-dependent, two-dimensional simulations based on random Voronoi networks have been developed to study the internal heating and related breakdown effects in ZnO varistors in response to high-voltage pulsing. The focus is on internal grain-size variations and relative disorder. Our results predict that parameters such as the device hold-off voltage, the average internal temperature, and average dissipated energy density would be higher with more uniform grains. This uniformity is also predicted to produce lower thermal stresses and to allow for the application of longer duration pulses. Finally, it is shown that the principle failure mechanism arises from internal localized melting, while thermal stresses are well below the thresholds for cracking.
+ Electro-Thermal Simulation Studies For Pulsed Voltage Induced Energy Absorption And Potential Failure In Nficrostructured Zno Varistors
  Joshi, RP; Zhao, G; Song, J; Lakdawala, VK
Abstract:  Time-dependent, two-dimensional simulations based on random Voronoi networks have been developed to study the internal heating and related breakdown effects in ZnO varistors in response to high-voltage pulsing. Our simulations allow for dynamic predictions of internal failures and the progression of hot-spots and thermal stresses. Results show that application of high voltage pulses can lead to the attainment of Bi2O3 melting temperatures in the grain boundaries and an accelerated progression towards failure. It is argued that reduction in grain size would help lower the maximum internal stress and enhance the hold-off voltage for a given sample size.
+ Electro-Thermal, Transient, Mixed-Mode 2D Simulation Study Of Sic Power Thyristors Operating Under Pulsedpower Conditions
  Hillkirk, LM; Hefner, AR; Dutton, RW; Bayne, SB; O'Brien, H
Abstract:  An electro-thermal, transient device simulation study of Silicon Carbide (SiC) power thyristors operating in a pulsed-power circuit at extremely high current density has been carried out within the drift-diffusion approximation and classical heat generation and transport theory using MEDICI* [1]. The convergence problems normally associated with Technology Computer-Aided Design (TCAD) simulations of SiC bipolar devices were overcome without artificially increasing the free carrier concentration by optical carrier generation. or by increasing the initial temperature (thermal carrier generation). The simulation results closely predict the actual operating conditions of the SiC thyristor in the pulsed-power circuit and are used to interpret the results of experimental failure limit studies [2]. It is shown that TCAD simulations can realistically predict the electrical and thermal properties of complex SiC bipolar semiconductor devices operating under fast transient, pulsed-power conditions.
+ Evaluation Of Switch Jitter In A High Pressure Coaxial Spark Gap
  James, C; Dickens, J; Holt, S; Kristiansen, M
Abstract:  The design and jitter performance of a high-pressure, coaxial spark gap, triggered by field distortion by a center plane electrode is presented. Additional comparisons with trigatron style triggering are also presented. The switch was tested up to 100 pulses per second (pps) with a maximum switching voltage of 50 kV in nitrogen. Analysis will focus on jitter measurements taken over the full lifetime of the switch. This paper presents the results of this analysis. Specifically, switch jitter and lifetime will be evaluated as a function of switch geometry as a whole and as a function of trigger electrode geometry.
+ Evaluation Of The Safe Operating Area Of A 2.0 Cm2, 4 Kv Si Sgto
  H. O'Brien; S. B. Bayne; W. Shaheen; T. Crowley
Abstract:  Summary form only given. The U. S. Army Research Laboratory (ARL) has been evaluating high voltage, high current modular silicon super-GTOs (SGTOs) developed by Silicon Power Corporation (SPCO) for ARL. The modular approach, combining SGTO die in parallel and in series, has been successful for devices implemented in both 10 kV, 80 kA and 10 kV, 400 kA configurations. It is desirable to fully characterize the SGTOs at the individual chip level, though, in order to fully understand the capabilities of any scaled up device packages. To supply this study, SPCO modules containing eight Si die were altered so that each device could be switched independently while the other seven remained unused. Each SGTO was switched up to the point of destruction, which was evident in damage to the device's gate or to its anode-to-cathode high voltage blocking. SGTOs were pulsed in two separate test beds: one designed to produce narrow current pulses, and another designed for wider pulses approaching 1 ms. Peak current, rise time and action (I2t) limitations were evaluated across this spectrum of pulse widths to document the safe operating area (SOA) of the Si SGTOs. The peak current attained at a 2mus FWHM pulse width was 20 kA with a 10-90% rate-of-current rise time of 26 kA/mus. In the wider pulse circuit, single die were switched as high as 6.2 kA with an action value of 18 times 103 A2s. Waveforms for various SGTOs were analyzed, and a set of SOA curves was created to represent characterization of the SGTO die.

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+ Explosive Opening Switch Utilizing Shockwave Induced Conduction In Pmma And Pvc
  Lynn, C; Neuber, A; Dickens, J
Abstract:  It is known that PMMA and PVC become conductive under shock compression. However, to develop an opening switch, the material's recovery from conductor back to insulator is critical. Heating must be minimized in order to optimize recovery. Two sources of heat in this switch include shock induced heating and switch loss heating, which should be balanced for optimal results. Furthermore, it is also important to determine if the observed switching behavior is due to shock unloading or intrinsic material relaxation properties. In the extreme case of recovery, bulk breakdown may become an issue. This paper presents experimental data and discusses initial results as they relate to the development of an opening switch.
+ Fuse And Load Testing With Mid-Sized, High Energy Density Flux Compression Generators
  A. J. Young; T. A. Holt; M. A. Elsayed; A. A. Neuber; M. Kristiansen; L. L. Altgilbers; A. H. Stults
Abstract:  Compact pulsed power systems require power sources that are small in size yet can produce the necessary electrical energy required to drive the system. Helical magnetic flux compression generators (HFCGs) are attractive for single shot applications due to their rapid conversion of chemical energy to electrical energy. The small total volume of a generator coupled with the energy density of the fast-reacting high explosives makes mid-sized HFCGs an appealing option as sources in single shot compact pulsed power systems. Consistent output current and energy gain from shot to shot are key variables in the ability of an HFCG to drive compact pulsed power systems efficiently.

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+ Initiation Of Hpm Surface Flashover
  G. F. Edmiston; A. A. Neuber; J. T. Krile; L. McQuage; H. Krompholz
Abstract:  Summary form only given. Surface flashover formation at dielectric/air interfaces during pulsed high power microwave (HPM) excitation can severely limit the power densities which can be transmitted into atmospheric medium. Previous studies on HPM surface flashover in the S-band at 5 MW power levels have reported on the contributing factors to flashover development including the effects of gas type, pressure and relative humidity. Furthermore, analysis on optical emission spectra collected from the developing discharge has determined that the vibrational and rotational temperatures of the plasma are approximately 2700 degK and 300 degK, respectively. In addition to experimental efforts, a Monte Carlo-type electron motion simulation code, MC, has been developed to calculate the increasing electron density during flashover formation. Results from this code have exhibited a quantitative agreement with experimental data over a wide range of atmospheric conditions. A critical parameter to flashover development is the stochastic process involving the appearance of initiatory or "seed" electrons, as seen by the reduction in flashover delay time by approximately 10-20% in the presence of external UV illumination. While the current version of the MC code seeds the flashover location with electron densities on the order of background ion densities produced by cosmic radiation, it fails to incorporate the field assisted collisional detachment processes which are the primary origin of these electrons on the time scales of interest. Investigation of these processes and development of more accurate seeding in the MC code is a key step towards predicting HPM flashover over a wide range of parameters, particularly in the presence of highly electronegative gasses such as SF6 or O2, in which there is an absence of free electrons. Theoretical results of HPM surface flashover with the improved seeding model will be benchmarked against previously measured data obtained with HPM pulse excitation. Further, the slow rise-time data (~500-600 ns risetime) that revealed a distinct reduced field vs. pressure delay time product dependence will be supplemented by short rise-time pulse data.

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+ Investigation Of An Fcg And Pulse Transformer Based Power Conditioning System
  T. A. Holt; A. J. Young; M. A. Elsayed; A. A. Neuber; M. Kristiansen; K. A. O'Connor; R. D. Curry
Abstract:  A cooperative effort was initiated between Texas Tech University and the University of Missouri-Columbia to develop a single-shot power conditioning system to drive an RF load. The purpose of the system is to convert prime power to an output capable of driving a load with an impedance ranging from 15 to 30 Ohms. A Helical Flux Compression Generator (HFCG) was chosen as the electrical energy amplification stage due to its portability and high energy density. Certain topologies of HFCGs are better suited to drive low impedance loads (i.e. short circuits or similar), however, cascaded HFCG systems are capable of driving higher impedance loads, thereby reducing the requirements from subsequent pulse forming stages to match the HFCG output to the load impedance. Therefore, a dual-stage HFCG was chosen to drive a pulse transformer and series fuse in order to produce voltages on the order of 150 kV to 300 kV across the secondary of the pulse transformer. The fuse has been designed to open in 280 ns or less when a peak current of 25 kA-40 kA is reached. The output voltage will be used to drive an RF load or to charge a mesoband oscillator. Both topologies for power conditioning are being considered and tests to date indicate that both types of geometries can be driven by the HFCG and power conditioning system. The results of the experimental tests as well as the energy transfer efficiency will be discussed.

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+ Jitter And Recovery Rate Of A Triggered Spark Gap With High Pressure Gas Mixtures
  Y. -J. Chen; J. J. Mankowski; J. W. Walter; J. C. Dickens
Abstract:  Summary form only given. Recent attention in impulse antenna phased array has necessitated the need to develop a reliable high voltage, high repetition rate switch that will operate with ultra low jitter. An ideal jitter of a small fraction of the rise time is required to accurately synchronize the array to steer and preserve the rise time of the radiated pulse. This paper presents the impact, gases and gas mixtures have on switch performance which includes recovery rate and in particular, jitter. A 50 Omega, 2.4 nF pulse forming line is charged to 50 kV and provides the low inductance voltage source to test the different gases. Triggering is provided by an SOS voltage source that supplies >100 kV, 10 ns rise-time pulses at a rep rate up to 1 kHz in burst mode. A hermetically sealed spark gap with a Kel-F lining is used to house the switch and high pressure gas. The system will also introduce a high pressure gas mixing chamber that can mix various gases up to 2000 psi. Gases tested include dry air, H2, and SF6.

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+ Modeling Of A Single Element Pulsed Ring-Down Antenna For Implementation In A Phased Array System
  Belt, D; Mankowski, J; Walter, J; Dickens, J
Abstract:  A pulsed ring-down phased array antenna provides substantial energy deposition in the far field region in addition to a broad range main beam with scanning capabilities. This allows remote neutralization of Improvised Explosive Devices (IEDs) at far field distances and in virtually any direction. The pulsed ring-down antenna operates by charging the single element antenna with a high potential source and closing a switch to develop transient wave reflections on the antenna which then propagate in air. The performance of a pulsed ring-down phased array is highly contingent upon the design and performance of the individual antenna elements within the array. Such factors as operating voltage, antenna capacitance, material losses, antenna geometry and closing switch conductance characteristics must be examined for optimal performance to be achieved. By utilizing the COMSOL RF module transient analysis functions, we are able to characterize the various parameters beginning with a monopole and a dipole pulsed ring-down antenna operating in the hundreds of MHz range. We have examined and compared the results achieved from the experimental setup to the simulation model in order to better characterize the individual components of the antenna. We have also examined the discrepancies between an ideal closing switch and the experimental setup closing switch, which dramatically affects the far field range of the antenna. We have examined the material properties of the antenna to improve losses and increase system capacitance allowing an increase in the number of RF cycles per antenna discharge. With the results presented, an accurate model of pulsed ring-down antennas is available and will allow future development of more complex geometries that will improve the operation of pulsed ring-down phased array.
+ Pulse Evaluation Of High Voltage Sic Diodes
  H. O'Brien; S. B. Bayne; W. Shaheen; A. K. Agarwal
Abstract:  Summary form only given. The U.S. Army Research Laboratory is evaluating silicon carbide semiconductor components to determine the range of high power and pulsed power applications for which SiC is a sensible material to use. With SiC's tolerances for high temperatures and high current densities, compact modules of SiC diodes might be ideal for protecting other high power circuit components under pulse conditions. This study evaluated SiC diodes with a footprint of 0.73 cm2 which were designed bv Cree, Inc. and packaged and pulse tested at ARL. The diodes are rated for 6 kV blocking and 50 A of continuous forward current. They were arranged to clamp reverse currents at the switching end of a large capacitor bank and were pulsed at a single shot rate both individually and in parallel. Individual diodes were pulsed as high as 5.9 kA (corresponding to an action of 4.5 times 103 A2s) for 25 single shots before failing, and as high as 5.0 kA (with an action of 3.5 times 103 A2s) for over 100 shots without failure. Groups of diodes were characterized on a curve tracer and matched based on on-state dV/dl slope, which ranged from 3.7-4.0 mOmega. Five diodes paralleled in the pulse testbed carried a total current of 23 kA with each diode sharing 19-21% of the total peak current. Modules consisting of 8-10 diodes in parallel will be similarly pulsed to reach a peak total current of 40 kA and will ultimately be combined in a single, compact package for higher current applications.

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+ Pulsed Volume And Surface Discharges In An Sf6 Environment
  R. Vela; J. T. Krile; A. A. Neuber; H. G. Krompholz
Abstract:  Summary form only given. Volume and surface discharges in SF6 are investigated to support refurbishment of the Z-machine's laser triggered gas switch, LTGS, at Sandia National Laboratories (SNL). The recently upgraded LTGS has exhibited a failure mode which results in surface flashover on the inside of the dielectric switch envelope. These flashover events degrade the LTGS performance and cause a pre-fire in the successive shot. The principal physical mechanisms involved in surface flashover at various pressures of SF6 are therefore vital to the understanding of this specific switch failure mode. A 340 kV system was designed which replicated conditions found in the LTGS between two adjacent backbone electrodes. Besides measurement of flashover delay times for different dielectric materials (Lexan, acrylic, epoxies, etc.), emphasis was put on the detailed characterization of the flashover phenomenology. Hence, in addition to voltage and current diagnostics, fast optical imaging of the flashover along with the acquisition of optical emission spectra (~200 nm to 700 nm) was employed. One possible reason for the LTGS failure was thought to be ultraviolet (UV) radiation emitted from the volume discharge between the backbone electrodes, which could induce surface flashover on the inside of the envelope. Our present setup is utilized to gather evidence that would confirm this possibility by adding a field-stressed dielectric surface directly exposed to the volume arc produced between the model backbone electrodes. With a current amplitude as low as ~ 2 kA, the occurrence of sulfur and fluorine ions as well as hydrogen and carbon during dielectric surface flashover was revealed with optical emission spectroscopy. From the spectra, the plasma temperature was determined to be between 1.5 and 3 eV, largely depending on the SF6 pressure. The presence of carbon and hydrogen is of significance because it indicates removal of material from the dielectric surfaces during discharge. X-ray fluoroscopy has also confirmed sulfur deposits on the surfaces of the dielectrics tested. Experimental results with higher current amplitudes will be discussed as well as the results showing the UV's influence on inducing surface flashover in an SF6 environment.

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+ Short Pulse High Power Microwave Surface Flashover
  L. McQuage; G. Edmiston; J. Mankowski; A. Neuber
Abstract:  Summary form only given. High power microwave (HPM) surface flashover is investigated in order to gain a better understanding of this phenomenon and reduce the limitations it imposes on transmitted power levels. The experimental setup is designed to produce window flashover without the influence of a triple point. The HPM source for this testing is an experimental virtual cathode oscillator (vircator) capable of producing greater than 50 MW for 100 ns with an adjustable frequency from 3 to 5 GHz. This work builds on previous testing using a magnetron producing 5 MW for 4 mus at 2.85 GHz. The dominant modes of the vircator and magnetron are the circular TE11 and rectangular TE10 modes respectively, with the electric field component in both setups normal to the direction of propagation, yielding comparable conditions. Due to the large differences in output power and pulse length, the two setups operate in different regimes and mechanisms take on differing degrees of importance. Additional factors under investigation include gas pressure, composition, temperature, and air speed. Diagnostic equipment permits the analysis of power levels with sub-nanosecond resolution. Experimental results are compared with data from literature, previous testing, and Monte Carlo simulations.

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+ Testing Of High Energy Density Capacitors
  T. Crowley; W. Shaheen; S. Bayne; R. Jow
Abstract:  The U. S. Army Research Lab (ARL) is investigating the capabilities of high energy density capacitors at narrow pulse widths from two different manufacturers for high current pulsed power applications. Breakthroughs in this technology would allow smaller capacitor storage to be possible while retaining the same capabilities. The discharge pulse widths of the test shots were between thirteen and fourteen microseconds. These pulse widths were taken from the full wave half maximum pulse width (FWHM). Both capacitors are rated for 12.5 kJ of energy and are 250 μF but have different volumes. The General Atomics Capacitors (GA-ESI 38982, 38994) have a total energy density of 1.3 J/cc while the manufacturer B"™s capacitor has an energy density of 0.64 J/cc. Both General Atomics"™ and manufacturer B"™s capacitors are polypropylene metallized film capacitors. While energy density is a major concern for our tests; attributes such as peak current, rise time, and high voltage lifetime were other factors to be considered. ARL is collaborating directly with General Atomics to help provide input and data in order to improve all properties of their capacitors.

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+ Testing Of New Ferroelectric Elements Custom Engineered For Explosively Driven Ferroelectric Applications
  Holt, SL; Krile, JT; Hemmert, DJ; Hackenberger, WS; Alberta, EF; Walter, JW; Dickens, JC; Altgilbers, LL; Stults, AH
Abstract:  Explosively driven ferroelectric generators (FEGs) are reliable, compact, high voltage sources that utilize high pressures to liberate charge trapped in the crystal structure of ferroelectric materials. For the active ferroelectric element most FEG designs use commercial lead zirconate-titanate (PZT) compositions designed for either precision actuators or naval sonar transducers. However, the material properties that are important in FEG applications are not the same material properties for which these materials have been designed to maximize. FEG designs utilizing these commercial materials are performance limited by high voltage breakdown, mechanical failure and low energy densities. TRS Technologies inc. has produced a new series of ferroelectric elements designed specifically for FEG applications. HEM Technologies has performed dielectric strength and shock compression experiments on these new materials to evaluate their performance in comparison to existing commercially available materials.
+ Theoretical Pulsed Ring Down Antenna Array Performance
  Walter, J; Dickens, J; Mankowski, J; Kristiansen, M
Abstract:  High-power transient RF transmitters are currently being developed for multiple applications. One potential high-power pulsed source being considered is the pulsed ring-down source (PRDS). In a typical PRDS, electrical energy that is stored in the device structure is discharged through a switch, generating a damped ringing radiated waveform. The magnitude of the transmitted field is limited by parameters such as the overall device geometry and switch characteristics. The potential exists to increase the radiated far field power density by utilizing an array of PRDS transmitters. The performance of such an array depends on the triggering jitter of the device switches and the design of the individual radiating elements. The application of the array concept to pulsed ring-down sources using gas spark gap switches is examined. Theoretical array performance is discussed, taking into account practical switch jitter distributions.
Publication Year:  2006
+ A Bench Top Railgun With Distributed Energy Sources And Diagonostics
  B. T. McDaniel; J. J. Mankowski; D. Wetz; B. McHale; M. Kristiansen
Abstract:  The experimental results of a five stage distributed energy source railgun are presented. The advantages of such a scheme are increased efficiency due to less energy remaining in the railgun inductance and lower rail resistive losses. The design is a bench top 81 cm long solid armature railgun with a 1.27 cm × 1.27 cm bore cross-section separating the 1.27 cm × 2.54 cm copper rails. Multiple capacitive storage banks are connected at different positions along the length of the rails. Each bank is composed of electrolytic capacitors, toroidal inductors, SCRs, and free-wheeling diodes. The primary bank (stage 1) can store 11.6 kJ, and the other stages store 5.8 kJ of energy. The diagnostics include Rogowski coils at each bank, a flux ruler along the entire railgun to monitor the armature's velocity, and B-dots. The switches are controlled by pulsers with fiber optic inputs, which accurately trigger the SCRs. To sequence trigger the storage banks, B-dot sensors provide feedback to the armature's position. Additionally, experimental results are compared to PSPICE simulations.

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+ A Fabrication Method For A Mid-Sized, High-Energy-Density, Flux Compression Generator
  T. A. Holt; A. J. Young; A. A. Neuber; M. Kristiansen
Abstract:  Performance reproducibility is a necessity when considering sources for single-shot, high-voltage applications. Helical Flux Compression Generators (HFCGs) are attractive for a variety of single-shot applications and are capable of high energy amplification that can be used in conjunction with other pulse-shaping techniques such as an exploding wire fuse for achieving high output voltages [1,2]. Small scale HFCGs (with active volumes on the order of ~100-200 cm3), however, are known to perform unreliably from shot to shot [3] and can lose as much as 80% of the flux available in the system based on previous experience with small to mid-sized HFCGs [4]. The performance variation is often attributed to erratic armature expansion behavior and/or fabrication methods and tolerances [3, 4]. As the compressible volume increases, HFCGs are known to conserve more flux and perform more reliably [2]. A fabrication method is presented for a midsized (with active volumes on the order of ~300-400 cm3) dual-stage HFCG that aims to improve the reproducibility in shot to shot performance with the goal of increasing the appeal for use of HFCGs in single-shot pulsed-power applications. Results of experiments with inductive loads of ~3μH are discussed.

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+ A Flux Compression Generator Non-Explosive Test Bed For Explosive Opening Switches
  Belt, D; Mankowski, J; Neuber, A; Dickens, J; Kristiansen, M
Abstract:  Helical Flux Compression Generators (HFCG) of a 50 mm form factor have been shown to produce output energies on the order of ten times the seeded value and a typical deposited energy of 3 kJ into a 3 mu H inductor. Our previous work with a non-optimized fuse has produced similar to 100 kV into a 15. load, which leads into a regime relevant for High Power Microwave (HPM) systems. It is expected that similar to 300 kV can be achieved with the present 2-stage HFCG driving an inductive storage system with electro-exploding fuse. In order to optimize the electro-explosive wire fuse, we have constructed a non-explosive test bed which simulates the HFCG output with high accuracy. We have designed and implemented a capacitor based, magnetic switching scheme to generate the near exponential rise of the HFCG. The varying inductance approach utilizes 4 stages of inductance change and is based upon a piecewise linear regression model of the HFCG waveform. The non-explosive test bed will provide a more efficient method of component testing and has demonstrated positive initial fuse results.
+ Characterization Of Explosively Driven Ferroelectric Generator Material
  S. L. Holt; D. J. Hemmert; J. W. Walter; J. J. Mankowski; J. C. Dickens; M. Kristiansen; L. L. Altgilbers
Abstract:  Explosively driven ferroelectric generators (FEGs) are reliable, compact, high voltage sources for driving ultra-compact high power devices. When energized by mechanical stress, they release charge from their crystal structure, acting similar to a charged high voltage capacitor. However, due to the relatively low energy of these devices, they must be well matched to their application so that the full potential of the material can be utilized. This requires proper characterization of the material's electrical output as a function of the input shockwave. HEM Technologies and Texas Tech University characterized a ferroelectric ceramic, EDO EC-64, for different pressures to determine possible loss mechanisms and its maximum output power and energy.

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+ Evaluation Of 10 Kv, 80 Ka Si Sgto Switching Components For Army Pulsed Power Applications
  T. Crowley; H. O'Brien; W. Shaheen; S. B. Bayne
Abstract:  The U.S. Army Research Lab (ARL) is investigating the switching capabilities of advanced silicon devices for high current pulsed power applications. These solid state switches are intended to replace more traditional vacuum switches. The benefits of these switches are higher dl/dt, peak power levels and current densities, increased reliability and lifetime, and smaller switch volume. The peak current achieved by the device was 83.3 kA, with a 10% to 90% rise time of 3.5 mus while a 0.263 MA2s without failure. The peak power of the device during this test shot was 78.7 MW. ARL is collaborating with Silicon Power Corp. (SPCO) to evaluate super-GTO performance and improve upon switch/buss bar packaging for pulsed power applications

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+ Evaluation Of A 10 Kv, 400 Ka Si Sgto At High Di/Dt
  H. O'Brien; W. Shaheen; T. Crowley; S. B. Bayne
Abstract:  The evaluation of each 10 kV, 400 kA Si SGTO included a visual inspection and high-potting of each component module prior to pulsing. The complete unit was then switched in a low inductance RLC circuit to test voltage and current capabilities and maximize dl/dt. Devices were switched as many as 70 times without failure. Voltage sharing between the layers was within plusmn2%, and current sharing between the modules was plusmn5% of ideal sharing. The peak rate of current rise attained was 40 kA/mus, and the 50% pulse width of the current was 26 mus. The peak power switched was 1.06 GW, and the action of the forward current pulse reached 6.4 MA2s. This report includes details on the methods for evaluating the 400 kA SGTO, challenges faced and peak performance of the devices under single shot pulsing conditions

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+ Evaluation Of A 4 Mm X 4 Mm Sic Gto At Temperatures Up To 150°C And Varying Pulse Width
  H. O'Brien; W. Shaheen; S. B. Bayne
Abstract:  The U. S. Army Research Laboratory (ARL) is evaluating silicon carbide Super GTOs (SGTOs) to determine the extent of silicon carbide's capabilities as a possible replacement for silicon in future pulsed switching applications. Individual SiC die measuring 4 mmtimes4 mm were pulsed at high temperatures and varying pulse widths. These SGTOs were switched in an RLC circuit at temperatures up to 150 degC. At this peak temperature, they were switched as high as 3.2 kA and repetitively pulsed at 2.6 kA and 5 Hz for greater than 14,000 pulses. A pulse forming network (PFN) was also designed to increase the pulse width and the action seen by the SiC devices. At ambient temperature and a peak current of 2 kA, SiC SGTOs were switched in the PFN at a 50% pulse width of 40 mus and an action of 150 A2s. This report includes further data on high temperature and wide pulse width testing, as well as analysis of the devices' failure points

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+ Pressure Induced Conductivity For High Power Switching
  H. Veselka; A. Neuber; J. Dickens
Abstract:  Summary form only given. Investigations of shock induced conductivity of non-crystalline insulators and crystalline semiconductors were performed. Although we measured the insulator-to-metallic state transition time and conductivity, the focus of this investigation was on the recovery phase of the induced conductivity (i.e. metallic-to-insulator state transition). The recovery time and shock conditions were measured with high speed electrical diagnostics. The goal of this research is to determine the feasibility of using shock induced conductivity as a means of producing a high power opening switch. To minimize switch losses, the insulator-to-metallic transition time and conductance is also important, but has been more widely studied. Initial impact studies have shown that certain insulator can be conductive for 100 microseconds and recover under modest voltage less than one microsecond using a ten gram explosive charge. Various shock intensities are used in the study. The shock is produced primarily with conventional commercial explosives. In addition, the impact of sample thickness and compression duration on the induced the conductivity were also studied. The correlation between modest voltage and high voltage recovery time and shut-off current were studied

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+ Pulsed Unipolar Surface Flashover At Atmospheric Conditions
  Morales, K; Krile, J; Neuber, A; Krompholz, H; Dickens, J
Abstract:  Dielectric surface flashover along insulators in vacuum has been comprehensively researched over the years. However, the primary mechanisms involved in dielectric flashover at atmospheric pressures have yet to be as extensively analyzed with variable parameters such as electrode geometry, background gas, humidity, and temporal characteristics of the applied voltage. Understanding the fundamental physical mechanisms involved in surface flashover at atmospheric pressures is vital to characterizing and modeling the are behavior. Previous dc and unipolar excitation experiments have shown distinct arc behavior in air and nitrogen environments for an electrode geometry that produces electric field lines that curve above the dielectric surface. Specifically, flashover arcs in an air environment were observed to develop along the dielectric surface. Experiments conducted in nitrogen revealed that the arc developed along the electric field lines, above the surface of the dielectric. It was also of importance to alter the temporal characteristics of the applied voltage to simulate lightning situations and investigate the impact on the arc behavior and voltage delay times. A solid state high voltage pulser with an adjustable pulse width of similar to 500 ns at FWHM and amplitudes in excess of 30 kV was specifically developed to replicate the temporal characteristics of a voltage pulse observed when a building structure is hit by a lightning strike. Based on these results, the physical mechanisms primarily involved in pulsed unipolar surface flashover will be discussed. Additional studies regarding the effects of humidity and surface roughness on the flashover arc behavior will also be presented.
+ Rapid Capacitor Chargers For Rep-Rated Operation Of Low-Inductance Compact Marx Generators
  Giesselmann, M; McHale, B; Neuber, A
Abstract:  We designed and tested several rapid capacitor chargers for rep-rated operation of low-inductance, compact Marx generators with rep-rates ranging from 10 Hz to 100 Hz. All chargers are designed to be packaged in cylindrical volumes with inside diameters in the range of 5 in - 12 in. Our capacitor chargers are based on H-Bridge inverters using ultra fast 600V class IGBTs. The high voltage is obtained by driving step-up transformers with nano-crystalline cores at 30 kHz. These chargers are capable of average DC output power levels of more than 5 kW for short time operation, during which the thermal inertia of the IGBT assembly provides effective cooling (up to seconds). To achieve reliable rep-rated operation of the chargers, we developed HV feedback sensors to monitor the charging process and solid state Marx-style trigger generators to command trigger the discharge of the main Marx.
+ Real Time Feedback Control System For An Electromagnetic Launcher
  R. W. Karhi; J. J. Mankowski; D. J. Hemmert; S. L. Holt
Abstract:  The design and implementation of a real time feedback control system for a distributed energy, bench top, electromagnetic launcher is presented. The feedback control system provides optimum pulse shaping by real time control of solid state switches. Advantages of pulse shaping control include increased energy efficiency and control of armature exit velocity. Lab VIEW 8.0 software1 is used to program a National Instruments CompactRIO programmable automation controller (PAC). This provides real time processing by use of the reconfigurable I/O (RIO) FPGA technology. The program controls switch timing from analog feedback signals supplied by B-dot probes placed along the rail length. Through signal analysis, real time armature position is derived. The program uses this data to control pulse shape and width. A dedicated B-dot probe is placed at the beginning of each stage which is the desired triggering location. A flux ruler sensor along the bore length provides a secondary velocity calculation excluded from the control system. This sensor provides velocity measurements for every centimeter of bore travel. Collected data is used to characterize the system under test for different load conditions.

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+ Studies Of Tio2 Breakdown Under Pulsed Conditions
  Zhao, G; Joshi, RP; Lakdawala, VK; Schamiloglu, E; Hjalmarson, H
Abstract:  Model studies of current conduction and breakdown in TiO2 were carried out. Our simulation results indicate that electrical breakdown of TiO2 under multiple pulsed conditions can occur at lower voltages as compared to quasi-DC biasing. This is in agreement with experimental data. The results are indicative of a cumulative effect. We hypothesize that the lower breakdown voltages observed in TiO2 under pulsed conditions, is a direct rise-time effect, coupled with cummulative detrapping.
+ The Impact Of Water Conductivity, Electrode Material, And Electrode Surface Roughness On The Pulsed Breakdown Strength Of Water
  Wetz, D; Mankowski, J; McCauley, D; Dickens, J; Kristiansen, M
Abstract:  Experimental results are presented on the impact water conductivity, electrode material, and electrode surface roughness have on the dielectric strength of water. A 2 mm water gap was tested under pulsed conditions with maximum electric fields in excess of 1.5 MV/cm. Bruce profiled electrodes manufactured from various materials including Molybdenum, Aluminum, Copper, Tungsten, Nickel, Stainless Steel, and Zinc Oxide, which have work functions ranging from 4.2 eV to 5.3 eV, have been tested. The roughness average of the various surfaces was varied from 0.1 mu m to 1.96 mu m and the conductivity of the water within the gap was varied from I mu S/cm to 39 mu S/cm to determine the impact each has when tested in combination with the various electrode materials and surface roughnesses. Conclusions are made as to the effect each of these factors has on the holdoff strength of a water dielectric system.
+ Virtual Cathode Oscillator Component Optimization
  Y. Chen; J. Mankowski; J. Walter; M. Kristiansen
Abstract:  Recent research efforts at TTU include a simple aluminum cathode for E-beam generation in a virtual cathode oscillator (vircator). As a continuation of these results, we are fabricating and testing several different types of cathodes for the vircator driven by a Marx generator and a pulse forming line (400 kV, 60 ns, 30 Omega). The cathodes, each with an emitting area of ~32 cm2, are made from aluminum and oxygen free copper fashioned to similar geometries with either a chemical etch or a CNC machine process. The vircator is tested with all of these cathodes and evaluated for beam voltage, current, and HPM generation. In addition to the cathode testing, several stainless steel and tungsten anode meshes with varying transparencies (50%-80%) are evaluated

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Publication Year:  2005
+ A Compact, Repetitive, 500Kv, 500 J, Marx Generator
  A. A. Neuber; Y. J. Chen; J. C. Dickens; M. Kristiansen
Abstract:  The electrical characteristics and design features of a low inductance, compact, 500 kV, 500 J, 10 Hz repetition rate, Marx generator are discussed. While benefiting from the large energy density of mica capacitors, 4 mica capacitors were utilized in parallel per stage, keeping the parasitic inductance per stage low. Including the spark- gap switches, a stage inductance of 55 nH was measured, which translates with 100 nF capacitance per stage to ~18.5 Omega characteristic Marx impedance. Using solely inductors, ~1 mH each, as charging elements instead of resistors enabled charging the Marx within less than 100 ms with little charging losses. The pulse width of the Marx into a matched resistive load is about 200 ns with 50 ns rise-time. Repetitive HPM generation with the Marx directly driving a small Vircator has been verified. The Marx is fitted into a tube with 30 cm diameter and a total length of 0.7 m. We discuss the Marx operation at up to 21 kV charging voltage per stage, with repetition rates of up to 10 Hz in burst mode primarily into resistive loads. A lumped circuit description of the Marx is also given, closely matching the experimental results.

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+ Autonomous Rf Radiation Package For Various Applications
  W. J. Carey; A. J. Wiebe; D. D. Schwindt; L. L. Altgilbers; M. Giesselmann; B. McHale; K. Heinemann
Abstract:  The development of an autonomous RF radiation package for various applications is presented. This work is a coordinated effort to develop a tightly integrated unit, including the batteries, power supply, Marx generator, and plug and play antennas for various applications. ARC technology has designed the Marx generator and its associated high voltage antennas for this effort. Previous work by ARC has demonstrated 75 mm diameter, 700 mm length diameter Marx generators capable of delivering 200 kV pulses into 50 Omega coaxial cable with sub-nanosecond risetimes, enabling it to drive an antenna and generate high power microwaves. This technology has been re-designed into a reduced length geometry and augmented by inductive charging to permit pulse repetition rates. The antenna is incorporated directly onto the Marx output for efficient energy transfer and for compactness. This package has demonstrated peak electric field strengths up to 4700 V/m at 10 m. Texas Tech University has worked closely with ARC in developing a rapid charging power supply to meet stringent package constraints and still permit high pulse repetition rates. This system has already demonstrated the ability to charge a 50 nF capacitance up to 40 kV with a repetition frequency of 100 Hz, delivering an average power of 4 kW. This paper details the present status of the project, which will be completed in July, 2005. The cylindrical geometry of the final package has a diameter of 155 mm, a length of approximately 1500 mm without the antenna, and a mass of approximately 35 kg, depending upon the chosen antenna implementation. Results of preliminary tests are included.

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+ Evaluation Of A 7 Kv 80 Ka Sgto Module
  R. L. Thomas; H. O'Brien; W. Shaheen; S. B. Bayne
Abstract:  This work was undertaken to investigate the switching performance of Super GTO's (SGTO) under conditions of fast rise times up to 25 kA/us, high peak current up to 80 kA, blocking voltage of 7 kV and pulse width of 100 us. The device under test is a switch that is made of two 3.5 kV modules placed in series; each containing eight SGTO die in parallel. The SGTO die developed by Silicon Power Corporation (SPCO) have a very small gate structure of approximately 10 mum. The benefit of this small gate structure is that it allows the device to reach full conduction faster than a conventional thyristor and is therefore optimized for fast turn-on (high di/dt). The SGTO die is a very efficient device having a current density of 29.7 A/mm2 at 10 kA. Each SGTO die can hold of 3.5 kV and can conduct 10 kA. The efficiency of the SGTO die warrants evaluation of this dual module SGTO switch that is rated at 7 kV and 80 kA. The evaluation of the dual module will also determine its overall ability to be used in other voltage and current configurations for various applications by determining its safe operating area (SOA). We have evaluated the switch at 6 kV at a maximum current of 86 kA over a 120 mus pulse width and with a di/dt of 25 kA/mus.

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+ High Voltage Impulse Generator Using Hv-Igbts
  M. Giesselmann; B. Palmer; A. Neuber; J. Donlon
Abstract:  We are reporting on a High-Voltage Impulse Generator, which consists of a step-up transformer, which is driven by new HV-IGBTs (High-Voltage Isolated Gate Bipolar Transistors). The new HV-IGBTs are individually packaged silicon-dies intended for Pulsed-Power Applications. The silicon dies are normally packaged in large modules for locomotive motor drives and similar traction applications. In our work we used the Powerex QIS4506001 discrete IGBT and the QRS4506001 discrete diode, both with a nominal rating of 4500V/60A, derived from continuous- duty applications. Our experiments have shown that the devices are capable of handling currents in excess of 1 kA during pulsed operation.

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+ Multi-Frequency And Multi-Mode Microwave Identification In A Vircator Research
  X. Chen; J. C. Dickens; L. L. Hatfield; J. Mankowski; M. Kristiansen
Abstract:  In virtual cathode oscillator (VIRCATOR) research, multi-frequency and multi-mode microwaves are coupled out and propagate along a waveguide. Identifying the microwave propagating modes has become a priority work for further research on microwave radiation physical mechanisms. Generally, an antenna matrix at the end of an open waveguide, which can shape the radiated microwave power distribution, is used to identify the microwave propagating modes [1-2]. Actual microwave radiation mechanisms in a VIRCATOR are complicated. Multi-propagating modes and multifrequency microwaves coexist simultaneously, which challenges the antenna matrix method. In this paper, based on microwave propagating theory in a waveguide, a new method is proposed to identify multi-frequency and multi-mode microwaves, which is partially justified by the experimental data at Texas Tech University.

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+ Pulsed Dielectric Surface Flashover At Atmospheric Conditions
  K. P. Morales; J. T. Krile; A. A. Neuber; H. G. Krompholz
Abstract:  Dielectric flashover along insulators in vacuum has been sufficiently researched in the past. Less studied, but of similar importance, is surface flashover at atmospheric pressures and the impact of various electrode geometries, humidity, and type of gas present. Previous research has shown distinct arc behavior in air and nitrogen for an electrode geometry in which the electric field lines curve above the dielectric surface. Specifically, flashover experiments in nitrogen have shown that the arc path will follow the electric field lines, not the dielectric surface. As a result, it was concluded that the arc development path, whether along the electric field line or the surface of the dielectric, is related to the oxygen content in the atmospheric background. It is believed that this dependence is due to the arc's production of UV radiation in an oxygen rich environment. Further testing, in a pure nitrogen environment with UV illumination of the surface prior to the pulse application, has shown that UV plays a significant role in the arc development path. There is a near linear relationship between the percentage of liftoffs and the time delay between UV application and flashover. Additional studies have also shown a relationship between the UV intensity and the percentage of liftoffs. Based on these results we will discuss the physical mechanisms primarily involved in unipolar flashover at atmospheric pressure. Additional experimental results regarding the effects of humidity on the liftoff phenomenon will be presented as well.

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+ Pulsed Power Switching Of A 4 Mm × 4 Mm Sic Thyristor
  H. O'Brien; W. Shaheen; S. B. Bayne
Abstract:  While silicon carbide (SiC) is beginning to make its way into the low voltage (300-1200 V) commercial power diode market, its capabilities in pulse power applications have yet to be proven. A previous investigation by the U.S. Army Research Laboratory (ARL) of SiC GTOs suggested that this emerging technology could provide pulsed current densities 40 to 60 times greater than is obtainable in silicon-based switches [1]. This study continues that earlier work by examining 4 mm times 4 mm 4H-SiC thyristors designed by CREE Inc. to reach 1 kV and 4 kA. These devices were successfully switched up to 3.89 kA with a current density reaching 56.1 kA/cm2, a specific rate-of-current-rise of 49 kA/mus/cm2 (for peak rise-time 7.8 kA/mus) and a pulse-width ranging from 2.0 mus to 2.6 mus. The thyristors were tested at both single shot and repetitive switching rates up to 5 Hz. Device characteristics were mapped on a curve tracer at different stages of testing, and the failure of each thyristor was analyzed.

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+ Rapid Capacitor Charger For 10 Hz Operation Of A Low-Inductance Compact Marx Generator
  M. Giesselmann; B. McHale
Abstract:  We designed and build a rapid capacitor charger for 10 Hz, 500 J/shot operation of a low-inductance, compact Marx generator. The charger uses a hard-switched IGBT H-Bridge Inverter, which drives a 30 kHz, nano- crystalline step-up transformer. The transformer, in addition to the high-voltage rectifier and a trigger- transformer are contained in a section which is filled with transformer oil. The main circuit board also contains a solid-state Marx generator to trigger the main Marx generator. We also implemented a self-powered HV-feedback sensor to stop the charge process precisely at the target voltage. This new sensor greatly enhanced the rep-rated performance of the Marx by preventing pre-fires, since it enabled us to charge aggressively without overshooting the target voltage and have more time for spark-gap recovery.

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+ Silicon Carbide Power Semiconductor Module Development For A High Temperature 10Kw Ac Drive
  Katsis, D; Geil, B; Griffin, T; Koebke, G; Kaplan, S; Ovrebo, G; Bayne, S
Abstract:  A silicon carbide power module has been developed to demonstrate a high-temperature, 10kW AC drive application. Several goals for this development include temperature dependent parameter evaluation of parallel-connected transistors and junction barrier Schottky diodes at 150 degrees C operating temperature. Next, design of a high-thermal conductivity substrate to cool the modules based on predicted losses. Finally the integration into a variable speed AC drive using a DSP-based V/F motor controller. Test results for the 10 kW AC drive are provided to demonstrate power module performance up to 180 degrees C.
+ The Design Of A Broadband Microwave Pulse Calorimeter
  X. Chen; J. Mankowski; L. L. Hatfield; M. Kristiansen
Abstract:  In virtual cathode oscillator (VIRCATOR) research, the radiated microwave pulse is coupled out and propagates along a waveguide. The radiated microwave power is an important parameter to evaluate the oscillator design and is a prerequisite parameter to calculate the energy transferring efficiency. Because the radiated microwaves are an ultra-short pulse of multi-frequency in multi propagating modes, the power measurement is not easily manipulated. In this paper, a broadband calorimeter design with considerations of pulsed microwaves is presented. The design includes its material or medium selection, structure optimization and calibration.

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+ Thermal Performance Of Water-Cooled Heat Sinks: A Comparison Of Two Different Designs
  Salem, TE; Porschet, D; Bayne, SB
Abstract:  As power electronic applications continue to switch higher levels of voltage and current in smaller-sized component packages, the resulting increase in power density requires efficient thermal management. This paper compares the thermal performance for operating a MOSFET on a water-cooled pole-arrayed heat sink versus a novel water-cooled microchannel heat sink. Details are presented on an innovative technique for determining the thermal capacitance modeling parameter for the heat sinks from experimental data.
Publication Year:  2004
+ Evaluation Of 4H Sic Bipolar Junction Transistors
  Thomas, J; Kaplan, S; Bayne, S
Abstract:  4H-SiC bipolar junction transistors (BJTs) demonstrate excellent current carrying and blocking capabilities, and offer good high-temperature performance. Moreover, these devices are easier to parallel than their Si analogues due to negative current gain temperature coefficient. In contrast to vertical MOSFETs and JFETs, these devices do not have junction discontinuities in the active region, which makes these devices easily scalable to high blocking voltage requirements. This experiment will help MM2, F determine the safe operating areas of 1mm(2), 4mm(2), 9mm(2), and Darlington structure SiC BJTs constructed by CREE. The eventual goal of this work is to produce devices capable of blocking 1200V and operating at a maximum collector current of 10A. Ideally gains of 8 or more are desired at temperatures of 150 degrees C. These devices will be characterized at temperatures up to 150 degrees C. Next they will be put into a system containing a push-pull circuit, which will be used in to control the on and off states of the BJT under test. This report will serve as to document the operational status of the present devices and as feedback to CREE in order to guide the production of future devices. These devices were tested using single-shot and repetitive pulsing. The devices were tested individually, as well as in parallel pair configurations. During each of these experiments the devices were tested from room temperature to 150 degrees C.
+ Experimental Optimization Of A Reflex Triode Virtual Cathode Oscillator
  J. J. Mankowski; X. Chen; J. C. Dickens; M. Kristiansen
Abstract:  Experimental findings on a high power Reflex Triode Virtual Cathode Oscillator (Vircator) at Texas Tech University are reported. In order to optimize performance, changes to the AK gap distance were made. The AK gap was varied from 0.5 to 1.5 cm. The type of cathode material employed was velvet. Cathode radius was 2.5 cm. The Reflex Triode Vircator is driven by a 350 kV Marx generator with a 60 ns, 20 ohm pulsed forming line. Typical peak input power is 4 GW. The output microwave power is measured in the far-field with a waveguide to coax adapter. Thus far we have observed microwave peak power output as high as 330 MW corresponding to a peak power efficiency of ~ 11 %. In an effort to provide premodulation to the vircator region, reflecting strips were added in the downstream waveguide. This technique has been employed with success by this group with a coaxial Vircator.

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+ Fast, Transient Energy Extraction From High Frequency Ac-Alternators For Use In Electromagnetic Launch Applications.
  Giesselmann, M; McHale, B; Crawford, A
Abstract:  This paper describes work towards transient energy extraction from high frequency alternators to drive electromagnetic launchers through intelligent triggering of thyristors/Silicon Controlled Rectifiers (SCRs). The work was done using a 3-phase, 75 kVA level motor-generator set with a DC machine acting as the load. This system serves as a scale model to develop control techniques for full scale, multi-megajoule applications. With the use of a microcontroller and advanced sensors the system is able to maintain synchronization of the SCR converter with the generator voltage despite dynamically changing frequency and voltage distortion.
+ Forward And Reverse Recovery Spice Model Of A Jbs Silicon Carbide Diode
  Giesselmann, M; Edwards, R; Bayne, S; Kaplan, S; Shaffer, E
Abstract:  The charged controlled model is presented as an effective method to simulate junction barrier schottky (JBS) silicon carbide diodes. Proven as a valuable approach for silicon devices, this model can also account for wide bandgap energy semiconductors. The model was implemented in Orcad's SPICE software package using analog behavioral modelling. The simulation combines the efficiency of a traditional static model with an improved charge controlled model representing transient characteristics of the semiconductor due to stored charge in the depletion layer. The result is an enhanced model that simulates in short period of time. Parameter extraction methods are used to help identify saturation currents, capacitance, resistance, voltages, and modelling coefficients. The simulation results in a close fit to the data taken during reverse recovery of a JBS SiC diode.
+ Impact Of Surface Conditioning Of Large Area Electrodes On The Dielectric Strength Of Water
  Wetz, D; Mankowski, J; Truman, K; Kristiansen, M
Abstract:  Experimental results are presented on the impact electrode material and surface treatment has on the dielectric strength of water. A 4 mm water gap was tested under pulsed conditions with pulse widths greater than 1 mu s, peak electric fields over 2 MV/cm and peak currents over 15 kA. 304 stainless steel electrodes machined with a Bruce profile and an effective area of 5 cm(2) were tested with surface roughnesses ranging from .34 mu m to 1.41 mu m. Results comparing electrodes that have additionally been electropolished are compared to those without an additional treatment. These various surface treatments remove micro-protrusions from the electrode's surface which reduce field enhancements across the electrode surface. It is believed that this technique will minimize the number of breakdown initiation points thereby increasing the dielectric strength. Results are given on the degree to which. each finish improves the dielectric strength of water.
+ New Developments In High Power Capacitor Charging Technology
  Giesselmann, M; McHale, B; Heeren, T
Abstract:  This paper presents new advances in High-Voltage power supplies, which are used for rapid capacitor charging. We are developing very compact power supplies with input voltages of around 250 V and output voltages of 30-50 kV. The output power levels of these chargers are above 10 kW. These chargers are using state-of-the-art Isolated Gate Bipolar Transistors (IGBTs) as well as advanced packaging methods and other innovative circuitry. In addition, the size and weight of the step-up transformer has been significantly reduced. Design details as well as experimental results are presented.
+ Silvaco Modeling Of A 10Kv Sic P-I-N Diode
  Thomas, RL; Morgenstern, M; Bayne, SB
Abstract:  To maximize the benefit of semiconductor technology, the U.S. military is requiring that the operating temperature for power electronic devices must be able to handle temperatures of up to150 degrees C. Power devices that use the wide band gap material silicon carbide (SiC) are being developed to provide large breakdown voltages and fast recovery times. When circuits call for high blocking voltages and fast reverse recovery times under adverse temperature situations, the p-i-n diode is the device presently used. To simulate the SiC device behavior, a modeling program named Silvaco was used to characterize a 5.76mm(2) 10kV SiC p-i-n diode manufactured by Cree under forward bias, reverse blocking and reverse recovery conditions. These simulations are then compared with test results from the actual device. Forward bias testing of the diode was conducted on a high power curve tracer and two different test circuits were developed to test reverse blocking and reverse recovery conditions respectively on sample diodes from Cree to add credibility to the Silvaco simulations. The results from the simulation and the experimental test were compared to verify the accuracy of the simulation and improve the prediction of high temperature device behavior in power electronics.
+ The Effect Of Area On Pulsed Breakdown In Water
  Truman, K; Mankowski, J; Wetz, D; Kristiansen, M
Abstract:  Experimental results are presented on the degree to which electrode surface area impacts the dielectric strength of water. A water gap of 4 mm was tested under pulsed conditions with a maximum electric field in excess of 1 MV/cm and a maximum current of more than 20 kA. Stainless steel electrodes with a Bruce Profile were used to generate a uniform electric field across the water gap. The profile of the electrodes enabled effective areas ranging from 0.5 cm(2) to 75 cm(2) while minimizing the change in capacitance of the water gap. Conclusions are made as to the effect electrode surface area has on the holdoff voltage and holdoff time of water dielectric systems.
+ Thermal Evaluation Of Sic Gtos For Pulsed Power Applications
  Geil, BR; Bayne, SB; Ibitayo, D; Koebke, MG
Abstract:  For applications which require high peak current and fast rise time, Silicon Carbide (SiC) material is ideal due to its ability to tolerate high localized temperatures generated during switching. This research was performed to investigate SiC devices for pulse power applications and to analyze the failure of the devices. Seven 2 min x 2 mm SiC Gate Turn-Off thyristors (GTOs) manufactured by Cree were evaluated. The devices were tested at single shot and under repetitive stress using a ring-down capacitor discharge circuit. The current pulse width was 2 mu s with a peak current of 1.4 kA (current density of 94.6 kA/cm(2)) and a maximum di/dt of 2.36 kA/mu s. The maximum power dissipated within the devices was 240 kW. Thermal modeling of these devices was done using ANSYS to analyze the heating and cooling. The model used was a 2-D model that included the device package, and bonding materials. The maximum amount of power dissipated was calculated from the 1000 A, 2 ps pulse. No further power input was added to the model and the heat transfer was plotted on an exponential scale. It was found that heat applied to a 2 pin thick region of the fingers yielded a maximum temperature of 2,500 degrees C in the device. It took 1.0E(-02) seconds for this heat to dissipate and for the device to return to 23C. The minimum and maximum stresses were found to be -2.83E(+09) Pa and 4.06E(+08) Pa, respectively. It was also found that the thickness of the heat generation region did not affect the final time to cool, but did affect the maximum temperature reached.
Publication Year:  2003
+ Cavity Resonance Effect On A Coaxial Vircator
  Chen, XP; Dickens, J; Choi, EH; Mankowski, J; Hatfield, LL; Kristiansen, M
Abstract:  Traditionally, the radiated microwave frequency in a coaxial vircator is considered to be determined primarily by the virtual cathode oscillation frequency and the electron reflection frequency. However, some experiments at TTU show that the interaction between the virtual cathode oscillation and the cavity is a key in determining the microwave frequency and propagating mode. Particularly, we observe that the E-beam plays an important role in the cavity formation. Some possible explanations, including a virtual cavity concept, are proposed. The cavity resonance effect on a coaxial virtual cathode oscillator has been investigated in detail. The understanding of the E-beam characteristics is critical in optimizing the design of the cylindrical diode to avoid the microwave frequency shifting and mode competition.
+ Compact, High Power Capacitor Charger
  Giesselmann, M; Heeren, T; Helle, T
Abstract:  We are developing compact, high-power chargers for rapid charging of energy storage capacitors. The main application is presently rapid charging of the capacitors inside of compact Marx generators for rep-rated operation. Compact Marx generators produce output pulses with amplitudes above 300kV with ns or sub-ns rise-times. A typical application is the generation of High Power Microwaves. Initially all energy storage capacitors in a Marx generator are charged in parallel. During the so-called erection cycle, the capacitors are connected in series. The charging voltage in the parallel configuration is around 40-50kV. The input voltage of our charger is in the range of several hundred volts. Rapid charging of the capacitors in the parallel configuration will enable a high pulse repetition-rate of the compact Marx generator. The high power charger uses state-of-the-art IGBTs (Isolated Gate Bipolar Transistors) in an H-Bridge topology and a compact, high frequency transformer. The IGBTs and the associated controls are packaged for minimum weight and maximum power density. The packaging and device selection makes use of burst mode operation (thermal inertia) of the charger. The present charger is considerably smaller than the one presented in [1].
+ Compact, Portable Pulsed Power: Physics And Applications
  Gundersen, M; Dickens, J; Nunnally, W
Abstract:  We describe an academic research program designed to investigate fundamental issues that will impact future pulsed power technology. The project is intended to enhance the scientific footing for pulsed power, and to address issues in the development of compact, repetitive pulsed power. These include physics issues implicit in switch development, including both solid state and gas-phase, pulse generation at various levels from extremely small for fast high field generation to >100kV, and applications including ignition of jet fuels and biological response to electric fields.
+ Conductivity Measurements Of Explosively Shocked Aluminum And Ofhc Copper Used For Armature Material In A Magnetic Flux Compression Generator
  Hemmert, D; Mankowski, J; Rasty, J; Neuber, A; Dickens, J; Kristiansen, M
Abstract:  Modeling and characterization of a Magnetic Flux Compression Generator (MFCG) requires detailed knowledge of the changes in conductivity of the MFCG materials during the shock-loading phase. In the studies reported here, a thin metallic strip is shocked with an explosively generated shock wave produced from a charge of Composition C-4. The shock wave is intended to simulate the shock wave and pressures produced in MFCG research currently being conducted at Texas Tech University. These pressures are estimated to be between 1 and 3 GPa. The experimental setup is arranged so that the shapes of the metallic strip and shock front are the same, as confirmed using optical fibers. This was to ensure that the test sample was shocked uniformly. The metallic test strip is pulsed with a 70 A current pulse during application of the shock wave. The current and voltage across the test sample are measured directly to determine the change in conductivity. Pressure measurements are conducted in separate tests under similar conditions using strain gauges. The results are then compared to results determined previously using a Split Hopkinson Pressure Bar apparatus (SHPB).
+ Design Criteria For Prevention Of Armature Turn-Skipping In Helical Magnetic Flux Compression Generators
  Rasty, J; Le, X; Dickens, J; Neuber, A; Kristiansen, M
Abstract:  Helical Magnetic Flux Compression Generators (MFCGs) are capable of producing ultra-high power electric pulses by trapping and compressing a seed magnetic field into a load coil via an explosive-driven armature. The efficiency of helical MFCGs is generally very low, about 10%, due to large magnetic flux losses. One of the main sources of magnetic flux loss is the turn-skipping phenomenon, in which the expanding armature fails to establish contact with every turn of the helical coil, resulting in magnetic flux loss in the skipped turns of the coil. The turn-skipping phenomenon is related to non-uniform or asymmetric expansion of the armature, as well as detonation end effects, Equations describing the turn-skipping phenomenon are developed in terms of the eccentricity of the armature with respect to the helical coil, the armature's wall thickness variations and the length of the detonation end effect. Design criteria for prevention of turn-skipping are presented in order to achieve optimum MFCG performance.
+ Effects Of Electrical Pulses On The Dielectric Properties Of Biological Cells
  Garner, AL; Yang, J; Chen, N; Kolb, J; Loftin, KC; Swanson, RJ; Beebe, S; Joshi, RP; Schoenbach, KH
Abstract:  Despite a basic knowledge of cells' biochemical processes, their electrical properties, particularly the changes in membrane properties upon the application of pulsed electric fields (PEF's), have not yet been fully characterized. Microsecond pulses above a certain threshold cause electroporation of the cell membrane while nanosecond pulses of higher voltage additionally porate the inner organelles. We used Time Domain Dielectric Spectroscopy to measure the conductivity of HL-60 (human leukemia) cell suspensions as a function of time after 10 ns, 78.5 kV/cm pulses and 50 mus, 1.1 kV/cm pulses, which have the same energy. The conductivity increased immediately after the 50 mus pulse, indicating that ion channels in the HL-60 membranes initially opened. However, the conductivity decreased immediately after the ultrashort pulse, indicating that ion channels initially closed. The conductivity decreases significantly approximately 40 minutes after both pulses. This suggests that not only do the pores or channels opened close, but pores or channels open in the membrane prior to the pulse may close as well. These measurements were an intermediate step in determining the electrical properties of HL-60 cells using a two-shell model. Once determined, these electrical parameters will be used in electroporation models developed at Old Dominion University.
+ Efficiency Results From A Coaxial Vircator Using A Simple Feedback Technique
  Mankowski, J; Cheng, X; Dickens, J; Kristiansen, M; Choi, E
Abstract:  Experimental findings on the coaxial virtual cathode oscillator (Vircator) at Texas Tech University are reported. A major modification to the system extended the pulse forming line several meters. The pulsed power system now delivers up to 750 kV and 60 kA for at least 70 nsec. Additional modifications include diagnostics to measure the diode voltage, current, and radiated field pattern of the output microwaves. In this initial phase of experiments copper reflectors were installed within the diode to provide a simple means of microwave feedback to assist in the e-beam modulation. Thus far we have observed microwave peak power output with feedback reflectors as high as 3.5 GW corresponding to an efficiency of similar to9.5%. Measured radiated field patterns show evidence of multi-mode operation.
+ Evaluation Of Sic Gtos For Pulse Power Switching
  Bayne, SB; Ibitayo, D
Abstract:  Certain applications require devices that can switch high peak current with fast rise times and narrow pulse width. This work was done as an initial study to investigate the performance of Silicon Carbide (SiC Gate turn-off thyristor (GTO) in these applications. The SiC GTOs were designed for high turn-off gain and not optimized for pulse applications. The GTOs were tested as discharge switches in a low inductance circuit delivering 2mus pulses with a maximum switching current of 1.4 kA (94.6 kA/cm(2)) and a current rise time of 2.4 kA/mus. All the devices were switched until failure. The failure modes will be discussed.
+ Fast, Real-Time Monitoring Of Ac-Alternators Under Heavy Transient Loading Conditionq
  Giesselmann, M; McHale, B; Crawford, M
Abstract:  This paper describes work towards controlling the output of fast AC-Alternators to drive transient loads through intelligent triggering of SCR (Thyristor) switches. The project entails the extension of methods and techniques that have been developed for high performance control of relatively small and slow turning industrial machines, to the more demanding regime of AC-machines used for kinetic energy storage and fast AC-servos for military applications. One of these techniques is a rotational transformation, where the (sinusoidal) AC output voltage of an alternator is converted to a DC level representing the instantaneous amplitude. This transformation, also called 'Vector Rotation' can be used for very fast observation of the momentary amplitudes of all electrical machine quantities, since no averaging is necessary. Through the use of vector rotations, advanced sensors and real time signal processing it is possible to demonstrate fast real-time monitoring of the energy extraction from a high frequency AC-Alternator with a full-bridge SCR converter. A low-voltage DC machine was selected as the load for the system, which closely resembles the transient impedance of an electric launcher.
+ Ferromagnetic And Ferroelectric Materials As Seed Sources For Magnetic Flux Compressors
  Schoeneberg, N; Walter, J; Neuber, A; Dickens, J; Kristiansen, M
Abstract:  An alternative to the use of capacitors as the seed source for flux compression generators (FCG) are permanent magnet based systems. Permanent magnets provide a larger energy-to-volume ratio given that the use of capacitors requires a power source as well as charging and firing circuitry. A recent design developed at Texas Tech University's Center for Pulsed Power and Power Electronics [1], focused on the demagnetization of a Neodymium-Iron-Boron magnet (Nd2Fe14B, B-r = 1.23 T) by a shockwave generated from high explosives. The maximum specific energy achieved with this design was only 2.3 J/kg, which may not be sufficient for effectively seeding an FCG (fast capacitors have at least 20 J/kg). The same magnets were used with an alternative design, referred to as a strip FCG, which utilizes opposing magnets to generate an initial magnetic field intensity within an air gap. The air gap exists between a central tube, filled with high explosives, and metal strips placed between the magnets a few millimeters off-axis. The detonation of the explosive causes the expansion of the central tube, subsequently compressing the flux into the strips and then into the load. The original strip FCG design [2] used oxide-barium magnets (B-r = 0.2T), which produced an estimated specific energy of 5.27 J/kg into a low inductance load. These magnets were replaced with the Nd2Fe14B (B-r = 1.23 T) magnets in order to achieve better performance, which will be analyzed with respect to the specific energy. In addition, a design utilizing a shocked ferroelectric material, PZT, as a seed current source is discussed. An explosively generated shock wave is passed through a ferroelectric material, generating a current that establishes the initial seed flux for an FCG. Preliminary tests of the ferroelectric sources indicate a possible theoretical specific energy of more than 11 J/kg or 25 J/dm(3). A comparison of the designs will be discussed with regard to the specific energy produced and the effectiveness of each to seed FCG's.
+ Investigation Of Pulse Power Thyristor Thermal Variations
  Hoffman, MG; Dickens, JC; Giesselmann, MG
Abstract:  This paper presents a study of temperature variations in a. Pulse Power Thyristor (PPT) during, and after discharge. The PPT studied was the SPT411BHT. The SPT411BHT is a 5000 V 4600 A, 125 mm thyristor made by Silicon Power Corporation. In order to determine the temperature of the PPT silicon, a 125 mm diode with identical thermal properties is placed in series with the PPT. There is a strict relationship between the forward voltage and the silicon temperature of the diode. Measurement of the forward voltage of the diode before and after discharge will accurately predict the temperature increase of the silicon. Peak discharge currents will be varied from 30 kA to 90 kA. The forward voltage measurement, circuit must be able to resolve millivolts in the presence of common mode voltages in excess of 2 W. Also, the circuit must isolate the measurement equipment from the circuit. This paper will discuss the temperature measurement concept as well as the design details of the circuit used to measure the diode forward voltage.
+ Investigation Of Ultra-High Switching Frequency To Reduce Size In Rapid Capacitor Charging
  Morris, BW; Dickens, JC
Abstract:  A compact high switching frequency rapid capacitor charging supply was designed and implemented. The challenges of topology design, component selection and implementation are discussed. The end goal is a supply capable of achieving 40kW at 40kV on the output and 100-300V input. The gate driver design is discussed with particular emphasis on gate voltage rise-time and propagation delay. Switching frequencies from 100 kHz to 1 MHz are explored. Transformer and output voltage multiplier designs are also described with expected performance parameters based upon computer simulations.
+ Nanosecond Laser-Triggered Microwave Switch
  McQuage, MM; Neuber, AA; Dickens, JC
Abstract:  The design and experimental testing of a laser-triggered microwave switch with a nanosecond activation time is described. The objectives of the project include, confirming that a nanosecond to sub-nanosecond risetime is achievable in the X-band waveguide at 9 GHz with the laser-triggered switch and to determine the minimum laser energy necessary to obtain the fastest possible risetime. A I kW pulsed X-band source with a 500 ns output pulse provides the microwave power for the system. A variable power Nd:YAG laser with a maximum 450 mJ at 532 rim, 10 ns FWHM output pulse is used in conjunction with an applied high voltage pulse to trigger the microwave switch. The microwave signal is switched with the rapid formation of plasma caused by the breakdown of a gas contained by a quartz tube inserted through a section of waveguide. The centerpiece of the waveguide system is a magic tee, which controls the direction of power flow through the system. Compared to tests in air and N-2, the best results have been obtained in Argon. Risetimes below 2 ns have been obtained using Argon at a reduced pressure of 150 Torr and a high voltage pulse of 28 kV from a spark gap. The impact of gas pressure, applied voltage pulse and applied laser pulse on the risetime of the microwave switch are discussed.
+ Nanosecond Pulsed Breakdown For Point-Plane Geometries At Moderate Voltage
  Krompholz, H; Hatfield, L; Haustein, M; Spears, J; Kristiansen, M
Abstract: 
+ Optical Diagnostics Of Liquid Nitrogen Volume Pre-Breakdown Events
  Butcher, M; Neuber, A; Krompholz, H; Dickens, J
Abstract:  An increased need for compact pulsed power systems requiring new switching technologies combined with the benefits of cryogenic properties, such as higher energy density and miniaturization, has lead to increased interest in liquid nitrogen as a switching medium. High hold off voltage, low dielectric constant, and low environmental impact are further advantages of liquid nitrogen. Characterization of breakdown is investigated using high-speed (temporal resolution < 1 ns) optical and electrical diagnostics in a coaxial system with 52 Omega impedance. Experiments are done in self-breakdown mode in supercooled liquid nitrogen with a temperature near 70 K. Discharge current and voltage are determined using transmission line type current sensors and capacitive voltage dividers. Discharge luminosity is measured with photomultiplier tubes (risetimeapproximate to800 ps) that are focused on the negative electrode tips and the center of the channel. Optical investigations of breakdown and pre-breakdown events on a nanosecond time scale will provide a better understanding of the fundamental physics of breakdown formation. Detailed optical and spectroscopic diagnostics combined with high-speed electrical diagnostics are aimed at clarifying the overall breakdown mechanisms, including electronic initiation and bubble formation. The breakdown initiation/development will be discussed.
+ Physical Efficiency Limits Of Inch-Sized Helical Mfcg'S
  Neuber, AA; Hernandez, JC; Holt, TA; Dickens, JC; Kristiansen, M
Abstract:  Helical Magnetic Flux Compression Generators (MFCG) are attractive energy sources with respect to their specific energy output. A variety of one-time use applications would benefit from small inch-sized helical generators with high specific energy output. However, it is widely accepted that the generator performance deteriorates with decreasing size. Previous experimental data have shown that the increase of the ohmic resistance of the MFCG with a reduction in size is the primary cause for the observed behavior when the initial generator inductance is held constant. We will analyze the situation in more depth and quantify how much the efficiency is determined by ohmic losses and intrinsic flux losses (flux that is left behind in the conductors and lost for compression) for different generator sizes and geometries. Our simple constant diameter MFCGs exhibit more intrinsic than ohmic losses (69% compared to 16%), while our MFCGs with tapered armatures display less intrinsic and more ohmic flux losses (13% compared to 66%), however, at increased overall efficiency. We will show experimental and calculated data and discuss the physical efficiency limits and scaling of generator performance at small sizes.
+ Physics Of Dielectric Surface Flashover At Atmospheric Pressure
  Krile, J; Neuber, A; Dickens, J; Krompholz, H
Abstract:  The limits of the applicability of dc, ac, or pulsed high voltage are determined by breakdown along insulators or insulating support structures. It is of major technical importance to predict breakdown voltages for given structures, with parameters such as geometry, material, and temporal characteristics of the applied voltage. The impact of atmospheric conditions such as humidity, pressure, temperature, and types of gas present is also important. A setup has been devised to simulate and closely monitor flashover across various gap distances and insulator geometries at atmospheric conditions at different humidities. Current, voltage, luminosity, and optical emission spectra were measured with nanosecond to sub-nanosecond resolution. Spatially and temporally resolved light emission data yielded quantitative information about the charge carrier amplification, the location of this amplification, and its role in the formation of streamers.
+ Pre-Breakdon Current Behavior In Dc Volume Breakdown In Transformer Oil
  Butcher, M; Neuber, A; Krompholz, H; Dickens, J
Abstract:  The phenomenology of pre-breakdown events in transformer oil is investigated using high-speed electrical and optical diagnostics. Data collection using a coaxial test setup terminating into a 50Omega load line to simulate a matched impedance system allows very fast risetimes. Transmission line type current sensors and capacitive voltage dividers with temporal resolution of 300 ps provide information about the discharge voltage and current. Steady, DC currents ranging from a few nA with less than 10 W of applied voltage, to a few muA prior to full breakdown are measured using an electrometer. Pre-breakdown events are measured with positive and negative charging voltages with respect to ground. Light emission from the discharge is measured using a series of fast photomultiplier tubes, (risetimes 800 ps), that observe positive and negative electrode tips and center of the channel. Preliminary results on self-breakdown (breakdown voltage +44kV) with a 2.35 mm gap show a DC (seed) current of several hundred nA with pre-breakdown spikes of a few mA immediately before final breakdown. Periodicity of the current spikes combined with a general increase in magnitude prior to full breakdown has been observed. Data collection using a negative charging line, with respect to ground with enhanced field at the cathode, indicates current spikes that are typically 25 to 50% faster than spikes using a positive charging line with enhanced field at the anode. Detailed optical diagnostics along with high-speed electrical diagnostics of the pre-breakdown phase will address the physical mechanisms initiating volume breakdown.
+ Reflex-Triode Geometry Of The Virtual-Cathode Oscillator
  Lara, MB; Mankowski, J; Dickens, J; Kristiansen, M
Abstract:  An eight-stage four-hundred kilovolt Marx bank, in connection with a 60 nanosecond pulse-forming line, is constructed and utilized as a pulsed source to power a planar version of the Virtual Cathode Oscillator (Vircator). Eight 1upsilonF capacitors, charged to 50kV each, are switched in series by dry-air pressurized spark gaps. The energy from the bank charges a 23 ohm oil transmission line, breaking a peaking gap when the maximum voltage is reached, delivering a 60 ns-300kV pulse to the diode. The design of the Planar or Reflex-Triode geometry Vircator is based upon claims of high efficiency by Didenko et al. A previously constructed TTU Vircator includes a unique E-beam source, the brush cathode; in which a circular array of pins is used as an explosive field emission source to produce relatively high beam currents. The anode consists of a round wire mesh through which the E-beam passes, generating a dense cloud of negative charge known as a Virtual Cathode. This initial phase of testing is composed of basic operation of the entire system and baseline output power and efficiency measurements.
+ Self Electrical Breakdown In Biodegradable Oil
  Cevallos, MD; Dickens, JC; Neuber, AA; Haustein, MA; Krompholz, HG
Abstract:  The fundamental breakdown physics of biodegradable oil is investigated with high speed electrical and optical diagnostics with temporal resolution down to several 100ps. The set up employs a cable discharge into a coaxial system with axial discharge and load line to simulate a matched terminating impedance. A unique feed-through design creates no discontinuities in the system lines through the discharge chamber. The impedance of the system is matched at 50 ohms including a novel design for impedance matching transitions from discharge cable to coaxial system to load line allowing for a sub-nanosecond response. This paper presents results on self breakdown with voltages of up to 60 kV. Self breakdown is achieved by charging the discharge cable and load line to +/-30 kV respectively. Transmission line type current sensors and a capacitive voltage divider with fast amplifiers/attenuators are used in order to obtain a complete range of information from amplitudes of 0.1 mA to 1kA with temporal resolutions of 300 ps. Optical measurements include high speed photography and shadowgraphy. Detailed optical diagnostics along with high speed electrical diagnostics will address the mechanism initiating/assisting biodegradable oil volume breakdown.
+ Short Pulse Electric Field Sterilization Of Liquid Media
  Wetz, D; Truman, K; Dickens, J; Mankowski, J; Neuber, A
Abstract:  In recent years, researchers have investigated methods of liquid sterilization by applying pulsed high electric fields with some degree of success(1-2). The mechanism by which microorganisms are damaged has been shown to be a function of the local electric field and exposure time while independent from thermal and electrolytic effects from the applied pulse. Most published experiments have employed electrical pulses of 10's of kV and microsecond long pulse lengths. We are employing electrical pulses in the 100's of kV range with 100 nanosecond long pulse lengths. This type pulse should be more effective at killing microorganisms and minimize energy losses due to thermal processes in the liquid media.
+ Silicon Vs Silicon Carbide Device Characterization
  Kaplan, S; Griffin, T; Bayne, S
Abstract:  Significant development of silicon carbide (SiC) material for device applications now allows circuit designers to more fully exploit its unique properties. The 4H-SiC structure provides the most favorable characteristics to optimize device speed and power handling capabilities. These include wide bandgap (3.2 eV), high dielectric breakdown (3.5 MV/cm), and high thermal conductivity (4.9 W/cm-K) [1]. By combining these properties, SiC devices are able to achieve fast reverse recovery and high reverse blocking voltages, along with excellent high temperature characteristics (case temperatures above 150 C). This makes these devices ideally suited to power electronics applications, where high power levels as well as fast switching are required. Many areas dominated by ultrafast recovery silicon (Si) diodes, might therefore be better suited to the application of SiC. In order to verify the efficacy of SiC devices, temperature dependent measurements were made on a sample of fast recovery Si and SiC diodes. This paper presents the results of these measurements, comparing critical characteristics of Si and SiC devices over a range of junction temperatures up to 150 C.
+ Single Shot Overstressing Of High Voltage Capacitors For Compact Arkadiev-Marx Generator
  Shkuratov, SI; Talantsev, EF; Dickens, JC; Kristiansen, M
Abstract:  Five different types of high voltage capacitors have been tested to determine their maximum high voltage overstress coefficient. Chicago Condenser, Reynolds Industries, Hivolt, and TDL capacitors of capacitance 100 nF and different nominal voltages were tested in the single shot mode. Experiments have shown that the energy stored under overstress conditions in all types of the capacitors tested is 10 to 20 times more than the nominal energy.
+ Small Sized Mfcg For Driving A High Impedance Load
  Hernandez, JC; Neuber, AA; Dickens, JC; Kristiansen, M
Abstract:  End-initiated small volume magnetic flux compression generators (MFCG) have at least one order of magnitude higher energy density (by weight or volume) than capacitive energy storage with similar discharge time characteristics. Since the prime energy is built into the MFCG in form of HE, the capacitor looses even more ground if the necessary prime energy source and the charging supply are included in the weight/ volume balance. However, simple MFCGs with a single helix produce high output energy only into low inductance loads, thus producing several 100 kA of current at a voltage level of only a few 10 kV. Many pulsed power devices require less current but a considerably higher voltage level. Two approaches for achieving a higher output voltage level, both utilizing two staged MFCGs, have been reported in the open literature. The first employs a more traditional transformer coupling, the second relies on a dynamic transformer or flux-trapping scheme. Although the traditional transformer coupling has theoretically the better efficiency, we chose the latter approach for our generator design, mostly since it requires a smaller number of components. Our generator has a total length of 250 mm, a helix inner diameter of 51 mm, and is wound with Teflon insulated stranded wire of different sizes in the range from AWG 12 to AWG 22. We have presently achieved an energy gain of similar to 8 and will discuss the generator performance based on experimental current/voltage waveforms.
+ Space-Charge Limited Current For 1-D Cylindrical Diodes
  Chen, XP; Dickens, J; Choi, EH; Kristiansen, M
Abstract:  By introducing a physics approximation method into analyzing the nonlinear Poisson's equation, an analytical expression for the space-charge-limited current density for a one-dimensional (1-D) cylindrical diode has been investigated and developed. This expression is different from Child-Langmuir law for the planar diode and is simpler than Langmuir-Blodgett law for the cylindrical diode. This expression builds an explicit connection between the current density and the physical parameters, which is helpful in optimizing the design of the cylindrical vacuum diode. In addition, a comparison between our analytical result and Langmuir-Blodgett law shows that the physics approximation method is valid in nonlinear differential equation analysis and can be used in other similar cases. Applying the approximation method, we get the relativistic theory corrected current for 1-D cylindrical diodes.
+ Surface Flashover Across Ceramic Disks In Vacuum At Cryogenic Temperatures
  Keene, H; Dickens, J; Neuber, A; Krompholz, H
Abstract:  As superconducting technology becomes more viable in the marketplace, especially in high power applications, the need for a well researched high thermal conductivity electrical insulator is needed. The electrical failure mode for these types of insulators is often surface flashover at sub-atmospheric temperature and pressure. Testing of two such insulators, aluminum nitride and aluminum oxide, for this failure mode is done for two differing electrode geometries. In addition three coats of GE 7031 dielectric varnish are applied to the exposed parts of the insulator for comparison testing with non-varnished samples. In general the testing shows an increasing breakdown voltage trend with decreasing temperature. These results indicate a temperature related dependence of the secondary electron emission and electron induced outgassing, which is a component in the process of surface flashover. The addition of the varnish results in a lowered breakdown voltage. The research also covers the effect of electrode conditioning, and presents optical diagnostics of the gas species involved during breakdown.
Publication Year:  2002
+ Dependence Of Flux Losses On Mcg Helix Geometry
  A. A. Neuber; T. Holt; J. -C. Hernandez; J. C. Dickens; M. Kristiansen
Abstract:  While Magneto Cumulative Generators (MCGs) differ widely in size and operating regimes, it is apparent that the helical flux compression generator is the most promising concept with respect to current amplification and compactness. Though the geometry of the helical generator (dynamically expanding armature in the center of a current carrying helix) seems to be basic, it turns out that the understanding of all involved processes is rather difficult. This fact is apparent from the present lack of a computer model that would be solely based on physical principles and manage without heuristic factors. This means, all programs known to the authors utilize an additional parameter that adjusts for the loss in flux that is currently unexplained. Experimental efforts revealed that the unexplained loss in flux becomes smaller the larger the generator volume is. Specifically, for generators with constant diameter helix and armature, the figure of merit, β, for generator performance exhibits a distinct decline with the angular frequency, ω, of the progressing contact between end-initiated armature and helix. Since ω is proportional to the square root of the ratio of initial MCG inductance to compressed volume, it becomes apparent that the generator performance is limited by size. For large generators on a meter scale, a β of approximately 0.95 has been reported (β = 1 means no flux loss at all), and own tests indicate that β drops quickly to about 0.7 to 0.6 for generator on the 10 cm scale. Still, even very small generators with about 30 mm outer diameter can have a β of around 0.6. Tapered generators, with tapered helix or tapered armature might perform differently and can be used to further assess the situation. Preliminary results for MCGs with a tapered helix show a performance that is somewhat superior to the straight helix generator.

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+ High Voltage, Sub Nanosecond Feedthrough Design For Liquid Breakdown Studies
  M. Cevallos; J. Dickens; A. Neuber; H. Krompholz
Abstract:  Experiments in self-breakdown mode and pulsed breakdown at high over-voltages in standard electrode geometries are performed for liquids to gain a better understanding of their fundamental breakdown physics. Different liquids of interest include liquids such as super-cooled liquid nitrogen, oils, glycerols and water. A typical setup employs a discharge chamber with a cable discharge into a coaxial system with axial discharge, and a load line to simulate a matched terminating impedance, thus providing a sub-nanosecond response. This study is focused on the feed-through design of the coaxial cable into this type of discharge chamber, with the feed-through being the critical element with respect to maximum hold-off voltage. Diverse feedthroughs were designed and simulated using Maxwell 3-D Field Simulator Version 5. Several geometrically shaped feed-through transitions were simulated, including linearly and exponentially tapered, to minimize electrostatic fields, thus ensuring that the discharge occurs in the volume of interest and not between the inner and outer conductor at the transition from the insulation of the coaxial cable to the liquid. All feedthroughs are designed to match the incoming impedance of the coaxial cable. The size of the feedthroughs will vary from liquid to liquid in order to match the coaxial cable impedance of 50Ω. The discharge chamber has two main ports where the feed-through will enter the chamber. Each feed-through is built through a flange that covers the two main ports. This allows the use of the same discharge chamber for various liquids by changing the flanges on the main ports to match the particular liquid. The feedthroughs were designed and built to withstand voltages of up to 200 kV. The feedthroughs are also fitted with transmission line type current sensors and capacitive voltage dividers with fast amplifiers/attenuators in order to attain a complete range of information from amplitudes of 0.1mA to 1 kA with a temporal resolution of 300 ps.

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+ High-Temperature Switching And Evaluation Of 4H-Sic Gate Turn-Off Thyristors And Diodes Under Inductive Loads
  Bayne, SB; Tipton, CW; Scozzie, CJ; Griffin, TE
Abstract:  Future U.S Army electric motor control applications will require power semiconductor devices that operate for thousands of hours at case temperatures of 150 degreesC and higher. For reliable operation of silicon (Si)-based power electronics, the case temperature must be below 120 degreesC. Because of this temperature limitation of Si, new wide bandgap materials, such as silicon carbide (SiC) are being investigated. We report on a SiC gate turn-off thyristor (GTO) and SiC p-i-n diode operating at case temperatures up to 150 degreesC. For high power and high voltage applications the GTO is the switch of choice. In this study, currents up to 2 A where switched by the GTO under pulsed and continuous switching into an inductive load. The turn-on and turn-off gains, the on-state voltage, and the turn-on and turn-off times, as a function of temperature will be discussed.
+ Liquid Nitrogen As Fast High Voltage Switching Medium
  Dickens, J; Neuber, A; Haustein, M; Krile, J; Krompholz, H
Abstract:  Compact pulsed power systems require new switching technologies. For high voltages, liquid nitrogen seems to be a suitable switching medium, with high hold-off voltage, low dielectric constant, and no need for pressurized systems as in high pressure gas switches. The discharge behavior in liquid nitrogen, such as breakdown voltages, formative times, current rise as function of voltage, recovery, etc. are virtually unknown, however. The phenomenology of breakdown in liquid nitrogen is investigated with high speed (temporal resolution < I ns) electrical and optical diagnostics, in a coaxial system with 50-Ohm impedance. Discharge current and voltage are determined with transmission line type current sensors and capacitive voltage dividers. The discharge luminosity is measured with photomultiplier tubes. Preliminary results of self-breakdown investigations (gap I nun, breakdown voltage 44 kV, non-boiling supercooled nitrogen) show a fast (2 ns) transition from an unknown current level to several mA, a long-duration (100 ns) phase with constant current superimposed by ns-spikes, and a final fast transition to the impedance limited current during several nanoseconds. The optical measurements will be expanded toward spectroscopy and high speed photography with the aim of clarifying the overall breakdown mechanisms, including electronic initiation, bubble formation, bubble dynamics, and their role in breakdown, for different electrode geometries (different macroscopic field enhancements).
+ Sub-Nanosecond Gas Breakdown Phenomena In The Voltage Regime Below 15 Kv
  Krompholz, H; Hatfield, L; Short, B; Kristiansen, M
Abstract:  Fast gaseous breakdown is of interest for both UWB/short pulse electromagnetics, and for plasma limiters to protect devices from high power microwave radiation. A quantitative investigation of fast breakdown phenomena, especially for relatively low voltages and for special geometries, does not exist to the authors' knowledge. Breakdown in gases is studied in a point-plane geometry with fast high voltage pulsers, covering the parameter range of voltage amplitude 1.7 to 7.5 kV, risetime 400 ps to 1 ns, and pulse duration 1 to 20 ns. The setup consists of a pulser, 50-Ohm transmission line, axial needle-plane gap with outer conductor, and 50-Ohm load line. The needle consists of tungsten and has a radius of curvature below 0.5 mum. The constant system impedance of 50 Ohm (except in the vicinity of the gap) and special transmission-line-type current sensors enables sub-nanosecond current and voltage measurements with a dynamic range covering several orders of magnitude. Digitizing oscilloscopes with sampling rates of 5 ps and 50 ps are used, with analog risetimes of 80 and 240 ps. In addition, the luminosity is measured with a sensitivity of about 10(8) V/W and a risetime of 800 ps. For pulse amplitudes of 1.7 kV (which are doubled at the open gap before breakdown), long pulse duration, and a gap distance of 1 mm, delay times between start of the pulse and start of a measurable current flow (amplitude > several milli-amperes) have a minimum of about 8 ns. The pressure dependence of this delay time was measured, in 10 to 600 torr argon, and a minimum is observed at 50 torr. Voltages of 7.5 kV produce breakdowns with a delay of about 1 ns. Statistical delays could not be found for either pulse amplitude, with the tip positively pulsed. With negative pulses applied to the tip, at an amplitude of 7.5 W, breakdown is always observed during the rising part of the pulse, with breakdown delay times below 800 ps. This delay time does not depend on the pressure, and points to a vacuum type discharge with field-emitted electrons as the dominant discharge mechanism for this case.
Publication Year:  2001
+ Advanced Modeling Of An Exploding Flux Compression Generator Using Lumped Element Models Of Magnetic Diffusion
  Giesselmann, M; Heeren, T; Neuber, A; Kristiansen, M
Abstract:  This paper describes an advanced PSpice model, which is used to complement the experimental work on explosive flux compression generators [1]. This work is conducted at Texas Tech University in the framework of a MURI program. The results from the model are compared to actual results from generators that have been tested in our laboratory. To achieve better fidelity of the model, the effect of transient current diffusion into the conductors of the generator is modeled by using a ladder network with many concentric layers of each current carrying conductor [3]. For the optimum accuracy, the spacing of the concentric layers is closest at the surface of the conductor. The paper shows results, comparisons with experimental data and applications of the model for the design of power conditioning systems for MFC-Generators.
+ Advanced Operational Techniques And Pn-Pn-Pn Structures For High-Power Silicon Carbide Gate Turns-Off Thyristors
  Shah, PB; Geil, BR; Ervin, ME; Griffin, TE; Bayne, S; Jones, KA; Oldham, TR
Abstract:  SIC GTO thyristors may soon be the best available choice for very high-power switching. At this time, we have developed new operational techniques, growth requirements and pn-pn-pn type structures to address the issues of high on-state voltage, poor turn-off gain, and inability to reach predicted breakover voltages. We present these findings using experimental measurements and numerical simulations.
+ Calculating Stator Losses In A Helical Mfcg
  Benton, T; Hsieh, KT; Stefani, F; Neuber, A; Kristiansen, M
Abstract:  This paper analyzes the transient electromagnetic, thermal, and structural behavior of the stator turns in a simple helical magnetic flux compression generator (MFCG). The main objective is to quantify the losses due to Ohmic heating and flux trapping in the conductors, including the effect of armature motion and armature proximity on the current distribution. The electric current excitation used in the modeling is based on experimental data from tests on a research MFCG. The electromagnetic (EM) and thermal analyses were conducted using EMAP3D, a 3D finite element analysis (FEA) code developed at The University of Texas at Austin (UT), which has the capability to model relative motion and sliding between conductors. Structural analyses were conducted using a version of DYNA3D that allows state data from EMAP3D to be used as input. Details of the analyses include temperature dependence on electrical, thermal, and mechanical properties.
+ Calculation Of Air Temperature And Pressure History During The Operation Of A Flux Compression Generator
  Le, XB; Rasty, J; Neuber, A; Dickens, J; Kristiansen, M
Abstract:  During the operation of Magnetic Flux Compression Generators (MFCG), the gas-plasma, shocked by the rapidly expanding armature, could lead to electrical arcing across the gas between the armature and the stator at locations where physical contact between the armature and stator has not yet occurred. This will result in a loss of magnetic flux and a decrease in the electrical efficiency of the MFCG. Therefore, knowledge of the ensuing gas temperature and pressure histories is necessary for identification of loss mechanisms in an effort to optimize the efficiency of MFCGs. This paper describes the procedure for estimating the air temperature and pressure histories via Finite Element (FE) simulation of the an-nature expansion and its ensuing contact with the stator in an MFCG. First, the validity of the FE model was verified by comparing deformation contours obtained from the simulations to those obtained experimentally via high-speed photography. Utilizing the pressure history data obtained from the FE results, the air temperature was theoretically calculated. The results indicate that the air pressure and temperature in an MFCG, having a compression ratio of 1.8, could be as high as 30 MPa and 4000degrees Kelvin, respectively.
+ Compact Design Of A 30 Kv Rapid Capacitor Charger
  Giesselmann, M; Kristiansen, E
Abstract:  This paper describes the downsizing potential of a power supply for charging a 7.2muF capacitor to a voltage of 30kV, which represents 3.24kJ of energy, in approximately 40ms. This process should be repeatable 10-20 times in a short burst mode within a time frame of a few minutes. The primary supply is a DC source with approximately 650V. A previous design achieved all these goals using 4 Semikron half-bridge IGBTs rated at 1200V/1200A each [1,2].
+ Compact Explosive Driven Shock Wave Ferromagnetic Generators
  Shkuratov, SI; Talantsev, EF; Kristiansen, M; Dickens, J; Hernandez, JC; Neuber, A
Abstract:  The results are presented of tests with compact, explosively driven shock wave ferromagnetic generators. The shock wave from high a explosive charge is passed along the axis of a cylindrical, hard magnet. Two types of permanent magnets were used in the experiments: rare-earth NdFeB cylinders (D = 2.5 cm, L = 1.9 cm) and hard ferrite BaFe2O3 cylinders (D = 2.2 cm, L = 2.5 cm). The shock wave demagnetizes the cylinder, reducing the flux from the remnant value to zero. This change in flux generates a voltage in the winding. The current generated in the loads of the generators yielded a peak of 0.75 kA. The operation of the shock wave ferromagnetic generators was analyzed by the Maxwell 3D code. An analysis is given on the specific features of pulse generation in a system like this.
+ Conductivity Measurements Of Mfcg Armature Material Under Shock And High Strain Rates Utilizing A Split-Hopkinson Pressure Bar Apparatus
  Hemmert, D; Rasty, J; Neuber, A; Dickens, J; Le, X; Kristiansen, M
Abstract:  Modeling and characterization of a Magnetic Flux Compression Generator (MFCG) requires detailed knowledge of the changes in conductivity of the MFCG materials during the shock-loading phase. A Split-Hopkinson Pressure Bar apparatus (SHPB) and current source/ differential amplifier setup was used to study shock-loading under controlled conditions while monitoring changes in resistivity in armature material samples. The SHPB apparatus was capable of producing strain rates up to the fracture limit of the samples tested. Actual fracturing of samples would not have allowed detailed analysis of thermal and mechanical effects in sample resistivity changes. Sample strain rate levels of up to 1x10(4) strain sec(-1) were achieved with the apparatus on OFHC copper and aluminum samples. This may be comparable to switching contacts under similar shock-loading and is an order of magnitude less than the expected strain rates in the MFCG. Sample resistivity showed an initial and abrupt decrease followed by a rapid increase during loading to levels twice that of virgin samples. Short and long time based resistivity monitoring and high speed framing photography allowed differentiation between changes in resistivity due to bulk material deformation, and changes due to thermal effects.
+ Effect Of Electron-Beam Pulse Length On Microwave Efficiency Of Coaxial Vircator
  Jiang, W; Woolverton, K; Dickens, J; Kristiansen, M
Abstract:  The coaxial virtual cathode oscillator (vircator) at Texas Tech University was studied by varying the pulse length of the electron beam. Previous experimental results obtained with electron beam pulse width of 25 ns have indicated that the microwave output power had not saturated before the electron beam power terminated. Therefore, it has been expected that the maximum microwave power can be increased if the electron beam pulse is lengthened. Experiments were carried out with the electron-beam pulse length of 25 ns and 70 ns, respectively, while keeping other parameters the same. The microwave outputs obtained with different electron-beam pulse lengths are compared in order to understand the effect of the pulse length on the microwave efficiency of the coaxial vircator.
+ Experimental And Numerical Investigation Of Armature/Stator Contact In Magnetic Flux Compression Generators
  Rasty, J; Le, XB; Neuber, A; Dickens, J; Kristiansen, M
Abstract:  The efficiency of a Magnetic Flux Compression Generators (MFCG) is highly dependent on the expanding characteristics of the exploding armature and the nature of contact between the armature and the surrounding stator coil. A hydrodynamic Finite Element (FE) model was developed to simulate the expansion characteristics of the armature and its ensuing impact with the stator. The effectiveness of the FE model to simulate the explosive behavior of the armature was qualified by comparing the numerical results with experimentally measured parameters. Specifically, the radial displacement of the armature as well as the axial velocity of the armature/stator contact point were measured experimentally and compared with numerical results showing excellent agreement between the two. The results indicated that the radial and axial velocity with which the armature impacted the stator did not change through the length of the armature. However, the results showed that the velocity with which the contact point between the armature and the stator traveled along the length of the armature decreased as the explosion process went on. As expected, the axial propagation velocity of the contact point was found to be at its highest value (2.25 X detonation velocity) at the region close to the detonation end while approaching the detonation velocity at points away from the detonation end.
+ Experimental Study Of Compact Explosive Driven Shock Wave Ferroelectric Generators
  Shkuratov, SI; Kristiansen, M; Dickens, J; Neuber, A; Altgilbers, LL; Tracy, PT; Tkach, Y
Abstract:  The design of explosive driven ferroelectric generators is presented and experimental data are discussed. The active elements are lead zirconium titanate (PZT) disks with diameter D = 25 mm and thicknesses H = 2.5 mm and H = 6 mm and PZT cylinders with D = 21 mm and H = 25 mm. The high explosive charge was varied from 4.2 g to 30 g. Two different ways to initiate shock waves in the active elements were used: explosively driven flyer plates and direct action of high explosives. The data presented is for the maximum power into a resistive load.
+ Explosive Driven Ferroelectric Generators
  Tkach, Y; Shkuratov, S; Dickens, J; Kiristiansen, M; Altgilbers, LL; Tracy, PT
Abstract:  Explosive Driven Ferroelectric Generators (EDFEGs) are compact power sources that have been considered for use as seed sources for magnetocumulative generators, as well as prime power sources [1,2]. Shock waves generated by high explosives arc used to shock depolarize ferroelectric materials, winch results in a voltage pulse being delivered to a load. These generators have been experimentally investigated at Texas Tech University. Data from these experiments was used to benchmark a code developed at the Institute of Electromagnetic Research. In this paper, a description of the simulation and a comparison of the experimental and simulation results will be presented.
+ Explosive-Driven Moving Magnet Generators
  Shkuratov, SI; Kristiansen, M; Dickens, J
Abstract:  The results are presented of experimental studies of explosively driven moving magnet generators. The study was performed with the use of high explosive and propellant charge. The projectiles used were NdFeB cylinders with D = 2.5 cm and H = 1.9 cm. Data are given for amplitude of high current pulses for different designs of the devices. The experiments performed have shown that the best option for generators using a moving magnetic projectile is to utilize the energy of the gases formed as a result of burning of the explosive rather than the energy of a flyer plate accelerated under the action of burning of the explosive. The explosive of preference is not C-4, but a military propellent charge which shows a high burning velocity and a high energy of explosive gases.
+ Gas Breakdown In The Sub-Nanosecond Regime With Voltages Below 15 Kv
  Krompholz, H; Hatfield, LL; Kristiansen, M; Hemmert, D; Short, B; Mankowski, J; Brown, M; Altgilbers, L
Abstract:  Gaseous breakdown in the sub-nanosecond regime is of interest for fast pulsed power switching, short pulse electromagnetics, and for plasma limiters to protect devices from high power microwave radiation. Previous investigations of sub-nanosecond breakdown were mainly limited to high-pressure gases or liquids, with applied voltages in excess of 100 kV. In this paper, we investigate possibilities to achieve sub-nanosecond breakdown at applied voltages below 7.5 kV in point-plane geometries. The setup consists of a pulser (risetime between 400 ps to l ns), 50-Omega transmission line, axial needle-plane gap with outer coaxial conductor, and a 50-Omega load line. The needle consists of tungsten and has a radius of curvature below 0.5 mum. The constant system impedance of 50 0 (except in the vicinity of the gap) and a special transmission-line-type current sensors enables current and voltage measurements with a dynamic range covering several orders of magnitude, with temporal resolution down to 80 ps. For pulse amplitudes of 1.7 kV (which are doubled at the open gap before breakdown) delay times between start of the pulse and start of a measurable current flow (amplitude > several milliamperes) have a minimum of about 8 ns, at a pressure of 50 torr in argon. Voltages of 7.5 kV produce breakdowns with a delay of about 1 ns. With negative pulses applied to the tip, at an amplitude of 7.5 kV, breakdown is always observed during the rising part of the pulse, with breakdown delay times below 800 ps, at pressures between 1 and 100 torr. At lower pressure, a longer delay time (8 ns at 50 mtorr) is observed. We expect the breakdown mechanism to be dominated by electron field emission, but still influenced by gaseous amplification.
+ High Current Testing Of Batteries
  Shkuratov, SI; Kristiansen, M; Dickens, J; Horrocks, E
Abstract:  Different types of commercial batteries were tested in a high-current mode to determine which is the best in portable pulsed power applications. The testing of the batteries was performed in two regimes: short time regime (one second) and long time regime (one hundred seconds). Alkaline, carbon, lithium, lithium ion, lead acid and nickel cadmium batteries of different dimensions have been tested to determine the maximum usable power for short and long time modes. The resistance of the load was varied from 1 Omega to 22 mOmega. Current-voltage characteristics are presented for sixteen different types of batteries. Data are given for maximum power per unit of weight and per unit of volume.Different types of commercial batteries were tested in a high-current mode to determine which is the best in portable pulsed power applications. The testing of the batteries was performed in two regimes: short time regime (one second) and long time regime (one hundred seconds). Alkaline, carbon, lithium, lithium ion, lead acid and nickel cadmium batteries of different dimensions have been tested to determine the maximum usable power for short and long time modes. The resistance of the load was varied from 1 Omega to 22 mOmega. Current-voltage characteristics are presented for sixteen different types of batteries. Data are given for maximum power per unit of weight and per unit of volume.
+ High Speed Optical Diagnostics Of An Exploding Wire Fuse For Power Conditioning Of Explosive Flux Compression Generators
  Giesselmann, M; Heeren, T; Neuber, A; Walter, J; Kristiansen, M
Abstract:  This paper presents high-speed optical diagnostics of an exploding wire fuse, which is used in the power conditioning system for an explosive flux compression generator. The images were taken using an IMACON(R) 790 high-speed framing camera utilizing a gated image intensifier tube. For our measurements, the camera was operated in the high-speed multiple frame mode, yielding 8-10 sequential, 2 dimensional pictures with 100 ns between exposures.
+ High Voltage Testing Of Capacitors
  Shkuratov, SI; Talantsev, EF; Kristiansen, M; Dickens, J
Abstract:  Three different types of capacitors have been tested to determine maximum usable high voltage. The capacitor testing was performed in the dynamic mode. The voltage rise varied from 200 to 400 V/sec. Disc ceramic and thin film capacitors of different value and different nominal voltages were tested. Experiments have shown that the breakdown voltage for all types of the capacitors tested is about ten times more than the nominal voltage of the capacitors. Data are given for the limiting high voltage for each kind of the capacitors. Experiments have shown that the mechanisms for the destruction of each type of capacitors have specific features.
+ Impact Of Helix Geometry On Mcg Flux Losses
  Holt, T; Neuber, A; Dickens, J; Kristiansen, M
Abstract:  Explosively driven magnetic flux compression has been the object of research for more than three decades. Recently heightened interest has been focused on the basic physical mechanisms that determine the performance of helical Magneto Cumulative Generators (MCGs). Two single-pitch helical flux compression generators of different sizes have been tested using current-voltage probes and optical diagnostics. The main parameters used to characterize the experimental performance of the flux compression generators were the flux conservation and theoretical current gain of each type of generator. Helices with constant pitch and differing separation between wires as well as wires with different insulation thickness were tested and analyzed with respect to their flux conservation and theoretical current gain. Preliminary results show that the insulation thickness plays only a minor role for a change in flux conservation due to geometry in the range from 0.01 to 0.5 min provided that no internal breakdown occurred. Additionally, the overall physical dimension of the generator was modified to allow for a substantial increase in initial inductance. The outer diameter of the generator armature was held constant at 1.5 inches and the coil diameter was varied from 2.6 to 3.5 inches (expansion ratio of 1.7 or 2.3, respectively). The results gained from the conservative expansion ratio of 1.7 were used as a base to compare to the generator performance at the more aggressive expansion ratio of 2.3. First results show that an expansion ratio of 2.3 produces viable results for a partially annealed Aluminum armature with a Gurney angle of approximately 15 degrees.
+ Parametric And Experimental Investigation Of The Edfeg
  Tkach, Y; Shkuratov, S; Dickens, J; Kristiansen, M; Altgilbers, LL; Tracy, PT
Abstract:  The objective of this effort was to investigate both parametrically and experimentally the properties of the Explosive Driven Ferroelectric Generator (EDFEG). The parametric investigation was conducted using a simulation developed by the Institute of Research (see paper P1-E31) and the experimental investigation using the explosive test facilites at Texas Tech University (see paper)OM. Both efforts were conducted synergistically in order to fully understand the characteristics of the EDFEG and to optimize its operation Results of both studies will be presented.
+ The Current Mode Of Pulsed Power Generation In Moving Magnet Systems
  Shkuratov, SI; Kristiansen, M; Dickens, J; Hernandez, JC
Abstract:  Results are presented of investigations of the generation of high-current pulses in moving magnet generators designed as an open ferromagnetic circuit. The experimental study was performed with the use of a light gas gun. The magnetic projectiles were ferromagnetic cylinders having 2.54-cm diameters. Data are given for the amplitude of high current pulses and power in the load for different designs of the devices, the effect of various windings on the pulse-generating coils, and different types of loads. It has been shown that with velocities of the magnetic projectiles of 200-300 m/s, the peak current of the pulses produced by the generators reach kiloamperes.
+ The Effect Of Multiple, Microsecond Electrical Pulses On Bacteria
  Aly, RE; Joshi, RP; Stark, RH; Schoenbach, KH; Beebe, SJ
Abstract:  Pulsed electric fields are widely used for bacterial decontamination of water and liquid food [1]. We have explored the effect of microsecond pulses of 13 kV/cm and 15 kV/cm electric field amplitude on the viability of Escherichia coli. Varied was the pulse duration from 4 mus to 32 mus, and the number of 4 mus pulses from one to eight, and finally the effect of the separation between pulses was studied. The pulse generator utilizes IGBTs as closing and opening switches. The maximum voltage was 1.5 kV, at a maximum current of 160 A. The load was a cuvette with plane 1 cm(2) aluminum electrodes, 1 mm apart and filled with a solution (LB Broth), which contained E. coli bacteria at a concentration of approximately 3x10(5) cells/ml. The viability of the E. coli after electric field application was measured by using manual counting for E. coli colonies in cultured agars. The bacterial decontamination rate was found to increase with pulse duration up to 8 mus and then to decrease again. This maximum in decontamination rate is assumed to be due to dipole formation in the rod shaped bacteria. It causes a reorientation of the E. coli into the direction of the electric field and consequently a higher possibility for irreversible damage. The experimental results with varying temporal separation between two subsequent pulses show that independent of field amplitude (in the relatively narrow range of 13 kV/cm to 15 kV/cm) the decontamination rate decreases logarithmically with increasing separation. The decay time constant was found to be approximately 10 ms. This effect is assumed to be due to the randomization of the axes-directions of the rod-shaped bacteria in the broth after exposed to an electric pulse.
Publication Year:  2000
+ Effect Of Blade Passing On A Wind Turbine Output
  Bayne, SB; Giesselmann, MG
Abstract:  Renewable energy such as wind and solar is a clean source of energy that can be integrated with conventional ways of producing energy. Power utility companies are looking at ways to integrate renewable energy with conventional methods. The Central and South West (CSW) renewable project was designed to investigate the role of solar and wind energy in a utility system. When connecting a wind farm to a utility grid, several issues must be taken into consideration such as stability, load matching, cost, location and the wind profile in relation to the peak loads on the system. One other parameter that is seldom considered is the effect of power oscillations due to turbine blades passing through their full are of motion and periodically encountering different wind speeds at different vertical positions. In the following, this effect is called 'blade passing' for short. This paper evaluates the effect of blade passing on the output voltage and current for a grid connected wind farm. The effect of blade passing as a function of the number of wind turbines connected to the grid is also investigated. The exact causes of the blade passing effect are also discussed.
+ Evaluation Of A Solid State Opening Switch (Sos) Diode Pulser For Use In A Electrochemical Reactor
  Giesselmann, M; Kristiansen, M; Grinstead, B; Wilson, M
Abstract:  A pulse generator, constructed by a group of Russian scientists, which is using a solid state opening switch (SOS), was characterized and tested, The diode acts similar to a step recovery diode but has voltage and current ratings that exceed the levels in US manufactured step-recovery diodes by orders of magnitude. To the authors knowledge, there are no US manufactured diodes for the application described here, With the load chosen for this paper, the generator produces pulses of 100 kV amplitude and 10 ns bah width, using a 600V DC supply. The maximum pulse repetition rate is 100 Hx, limited by thermal considerations of the primary charging resistor, This limit could be easily overcome by using a switch-mode power supply to charge the primary capacitors, This pulser can be used to generate partial discharges in a chemical reactor in order to produce Ozone for a variety of industrial uses such as sterilization, oxidation, NOx or SOx removal from exhaust gases, etc. The greatest advantage is the long lifetime of this all solid-state device.
+ High Power Microwave Window Breakdown Under Vacuum And Atmospheric Conditions
  Hemmert, D; Neuber, AA; Dickens, JC; Krompholz, H; Hatfield, LL; Kristiansen, M
Abstract:  Microwave window breakdown is investigated in vacuum and atmospheric conditions. An S-band resonant ring with a frequency of 2.85 GHz and a power of 80 MW with a 4 MW magnetron as a source is used. Window breakdown on the vacuum side is simulated using a dielectric slab partially filling an evacuated waveguide. Various high-speed diagnostic methods yield a complete picture on the breakdown phenomenology, with far reaching similarities to de surface flashover. During the initiation phase, free electrons are present, which can be influenced by magnetic fields, followed by a saturated secondary electron avalanche with electron-induced outgassing. Final breakdown occurs in the desorbed gas layer above the surface. In order to simulate window breakdown on the gas-side, a segment of the resonant ring separated by two windows was filled with gas at variable pressure, and breakdown was initiated by field-enhancement tips on one of the gas-side surfaces. Threshold power densities for breakdown are measured, and first results on the phenomenology of this gas breakdown are compared with the processes of flashover in vacuum.
+ The Use Of Thyristors For Repetitive Narrow Pulse, High Power Switching
  Bayne, SB; Portnoy, WM; Rohwein, GJ
Abstract:  Although high peak currents and fast risetimes can be simultaneously obtained for relatively short pulses in semiconductor thyristors have been obtained, no extensive study of thyristor operation under pulse conditions has been reported. This work demonstrates that reliable repetitive operation over millions of pulses can be obtained for pulse widths of around 1 ms.
Publication Year:  1998
+ Design, Construction And Test Of A 3-Phase Cryogenic Synchronous Rectifier
  Giesselmann, MG; Haider, MR
Abstract:  Prototypes of three-phase synchronous rectifiers using power MOSFETs including the necessary control circuitry have been developed and tested. Experimental results show a significant reduction of conduction losses at room temperature and large additional improvements if the MOSFETs are cooled with liquid nitrogen. The synchronous rectifier is proposed to be used as part of a power system for a next generation ground based radar (GBR) system.
Publication Year:  1997
+ A Subnanosecond High Voltage Pulser For The Investigation Of Dielectric Breakdown
  Mankowski, J; Dickens, J; Kristiansen, M
Abstract:  A high voltage, sub-nanosecond pulser is designed and built for the purposes of investigating dielectric breakdown. The requirement for the pulser is a voltage pulse of several hundred kilovolts, pulsewidth less than a few nanoseconds, and a risetime <400 psec. This is achieved by using pulse sharpening techniques on the output of a 500 kV Marx bank. Originally designed to stimulate a lightning strike, the voltage waveform from the Marx generator has a slow decay time of tens of mu sec. In order to obtain a more desirable pulse, the Marx bank is modified. By removing a lumped-element resistor a higher peak output voltage with a faster risetime can be obtained. Circuit simulations have shown the capability of achieving an 800 kV output in less than 40 nsec to a charging (pulse forming) line. The 50 Omega impedance, oil-filled, pulse forming line consists of a peaking gap and pulse slicing gap. The peaking gap decreases the risetime of the applied pulse down to about 300 psec. The pulse slicing gap is included to short the voltage applied to the delay line and test chamber.
+ Averaged And Cycle By Cycle Switching Models For Buck, Boost, Buck-Boost And Cuk Converters With Common Average Switch Model
  Giesselmann, MG
Abstract:  This paper shows computer models for common switch-mode converters with averaged and conventional cycle by cycle switching operation. Models for the Buck, Boost, Buck-Boost, and Cuk converter are presented. Also shown are Buck and Boost converters with integrated magnetic components. All time averaged models are using an identical averaged model for the PWM switch. The models are implemented using PSpice(R) for Windows(R). The advantage of averaged models are much faster execution time as well as the ability to perform frequency domain (bode plots) analysis in addition to time domain analysis.
+ Computer Simulations Of Coaxial Vircators
  Woolverton, K; Kristiansen, M; Hatfield, LL
Abstract:  A study of the efficiency of a coaxial virtual cathode oscillator is presented. The coaxial geometry has many physical parameters that can be changed to alter performance. The parameters of interest include the placement of a ring cut in the anode base and the polarity of the system. The ring creates a decelerating field for the electrons and tends to keep them in the right-phased region of the virtual cathode. The ring is varied in width and in position from the center line with the results normalized to the no ring geometry. The results for a positively and negatively pulsed system are also given. Comparisons of frequency, efficiency, and particle dynamics of the positively and negatively pulsed systems are given. MAGIC, a 2-1/2 dimensional particle-in-cell code, and SOS, a 3 dimensional particle-in-cell code, are used to simulate the different geometries.
+ Diode Polarity Experiments On A Coaxial Vircator
  Woolverton, K; Kristiansen, M; Hatfield, LL
Abstract:  A study on the interaction dynamics of a positively and negatively pulsed coaxial vircator is being performed at Texas Tech University. MAGIC, a 2.5D particle-in-cell code, is used to simulate the different geometries. The simulations performed indicate an increase in efficiency by approximately a factor of 2 for the negatively pulsed system compared to the positively pulsed system. Simulations are also performed to better understand the influencing factors of the systems. This paper describes the experimental results which are performed on a coaxial vircator with diode voltages from 400-500 kV at diode currents of 40-50 kA with pulse durations of similar to 50 nsec. Results that are given include microwave power, efficiency, spectral content and a possible explanation for the results.
+ Evaluation Of A Russian Sos Diode For Use In A Compact Modulator System
  Dickens, J; Kristiansen, M; Giesselmann, M; Kim, JG
Abstract:  A Russian Power Modulator, which is based on a diode that has been touted as a high power solid state opening switch (SOS) was characterized and tested. The diode has characteristics similar to those of a step-recovery diode, except that the reverse current density is 10-100 times larger than in US manufactured diodes. The modulator has a DC input voltage of 600 V and produces pulse of 150 kV amplitude and 25 ns half width into a 350 Omega load. The maximum pulse repetition rate is 100 Hz. The limit is given by thermal limitations and can be increased through the use of more effective cooling methods.
+ Neural Network For Wind Power Generation With Compressing Function
  Li, SH; Wunsch, DC; OHair, E; Giesselmann, MG
Abstract:  The power generated by electric wind turbines changes rapidly because of the continuous fluctuation of wind speed and direction. It is important for the power industry to have the capability to estimate this changing power. In this paper, the characteristics of wind power generation are studied and a neural network is used to estimate it. We use real windfarm data to demonstrate a neural network solution for this problem, and show that the network can estimate power even in changing wind conditions.
+ Neurobiology Of Pheromonal Signal Processing In Insects
  Dickens, JC
Abstract: 
+ Operating Experience With A High Throughput Jet Generator
  McDermott, WE; Stephens, JC; Vetrovec, J; Dickerson, RA
Abstract:  Over the last several years, Rocketdyne has conducted a number of experiments on advanced jet generators. Both Gross flow jet generator and counter flow jet generators have been tested. We have made laser power measurements at our Continuous Wave Chemical Laser Facility (CWLL) and at the Air Force Phillips Laboratory RADICL test facility. A test there resulted in a measured chemical efficiency of 29.6%. This is the highest efficiency reported for a supersonic oxygen-iodine chemical laser.
+ Streamer Discharges By Pulsed Power On A Spiral Transmission Line
  Akiyama, H; Nishihashi, Y; Tsukamoto, S; Sueda, T; Katsuki, S; Hagler, M; Dickens, JC; Inoue, N
Abstract:  Streamer corona discharges produced by pulsed power make enough high energy electrons to dissociate gases directly. Consequently, pulsed streamer discharges have been proposed for the removal of NOx and SO2 from flue gases, the production of ozone and the treatment of poisonous gases. It is proposed here to produce the pulsed streamer discharges on a spiral transmission line. The characteristics of the discharges are studied, comparing with results using a PSpice code. Then, the effectiveness and advantages of the spiral transmission line are discussed in view of real applications.
+ Window And Cavity Breakdown Caused By High Power Microwaves
  Neuber, A; Dickens, J; Hemmert, D; Krompholz, H; Hatfield, LL; Kristiansen, M
Abstract:  Physical mechanisms leading to microwave breakdown on windows and in cavities are investigated for power levels on the order of 100 MW at 2.85 GHz. The test stand uses a 3 MW magnetron coupled to an S-band traveling wave resonator. Various configurations of dielectric windows are investigated. In a standard pillbox geometry with a pressure of less than 10(-8) torr, surface discharges on an alumina window and multipactor-like discharges starting at the waveguide edges occur simultaneously. To clarify physical mechanisms, window breakdown with purely tangential electrical microwave fields is investigated for special geometries. Other configurations, such as air filled two window setups, relevant for vacuum-air interfaces, can be investigated as well. Diagnostics include the measurement of incident/reflected power, measurement of local microwave fields, discharge luminosity, and x-ray emission. All quantities are recorded with 0.2 to 1 ns resolution. In addition, a framing camera with gating times of 5 ns is used. Based on the experimental results, methods to increase the power density which can be transmitted through windows, such as surface coatings and window profiles, will be investigated as well.
Publication Year:  1996
+ A Review Of Catastrophic Electromagnetic Breakdown For Short Pulse Widths
  Agee, FJ; Scholfield, DW; Copeland, RP; Martin, TH; Carroll, JJ; Mankowski, JJ; Kristiansen, M; Hatfield, LL
Abstract: 
+ Breakdown At Window Interfaces Caused By High Power Microwave Fields
  Dickens, JC; Elliott, J; Hatfield, LL; Kristiansen, M; Krompholz, H
Abstract: 
+ Compact Modulator Using Inductive Energy Storage And A Solid State Opening Switch
  Dickens, JC; Bridges, J; Kristiansen, M
Abstract:  A compact modulator system using inductive energy storage and a diode as an opening switch was investigated. The system was designed around a Russian diode that has characteristics similar to those of a step-recovery diode except that the reverse current density is 10-100 times larger than in U.S. manufactured diodes. The main goal of this investigation was to characterize the Russian diode and develop an understanding of its operation for possible improvement and integration into nanosecond pulse generators. The basic modulator circuit designed uses IGBT's in the forward pumping circuit and is capable of delivering 5 kV at 400 A into the diode. Using this forward pumping circuit, diode voltage and current measurements were made at several input power levels. In addition, data obtained using this test stand was used to produce a computer simulation model of the diode for a more thorough circuit analysis.
+ Design And Construction Of A Neutral Point Clamped Inverter
  Giesselmann, M; Crittenden, B
Abstract:  The design and construction of a Neutral Point Clamped Inverter along with its modulation strategy and circuit simulation using PSPICE 6.2 for Windows is presented. This inverter is a subscale (100 kW) prototype for a inverter that is intended to be used in a 1MW level universal power converter system to produce 3 phase AC power at 60 Hz from variable input sources.
+ Dynamic Modeling Of Switched Reluctance Machines With Pspice For Windows
  Giesselmann, MG
Abstract: 
+ Investigation Of Power Mosfet Switching At Cryogenic Temperatures
  Giesselmann, M; Mahmud, Z; Carson, S
Abstract:  Operation of power MOSFETs (Metal Oxide Semiconductor Field Effect Transistor) at cryogenic temperatures significantly reduces conduction losses and increases power handling capability. High voltage (1000V+) devices exhibit the largest reduction of conduction losses. The breakdown voltage of the devices is reduced by about 20% when cooled from 75 degrees F down to -319 degrees F.
Publication Year:  1995
+ Insulator Surface Flashover With Uv And Plasma Background And External Magnetic Field
  Hegeler, F; Krompholz, H; Hatfield, LL; Kristiansen, M
Abstract: 
+ Low Frequency Inductive Heating Of A Rigid Track During Track Laying
  Miedzinski, B; Okraszewski, Z; Szymanski, A; Kristiansen, M
Abstract: 
Publication Year:  1994
+ Development Of Induction Motors Drives With Real Time Pwm Control And Dynamic Modeling Of Drive Performance With Graphical User Interface
  CHOWDHURY, G; GIESSELMANN, M
Abstract: 
+ Mass Erosion And Surface Voltage Holdoff Recovery Of Insulators Used In A High-Current, High-Vacuum Surface Discharge Switch
  ENGEL, TG; WESTER, SL; KRISTIANSEN, M; HATFIELD, LL
Abstract: 
+ The Early Phase Of Dielectric Surface Flashover In A Simulated Low Earth Orbit Environment
  HEGELER, F; KROMPHOLZ, H; HATFIELD, LL; KRISTIANSEN, M
Abstract: 
Publication Year:  1993
+ Development Of Next-Generation Intelligent Power Modules For Induction-Motor Drives And Dynamic Modeling Of Machine Behavior
  GIESSELMANN, M; ELDRED, C; SEITZ, D
Abstract: 
+ Electrode Performance Of A 3 Electrode Triggered High Energy Spark Gap Switch
  DICKENS, JC; ENGEL, TG; KRISTIANSEN, M
Abstract: 
+ High Power, Electron-Beam Induced Switching In Diamond
  SCARPETTI, RD; HOFER, WW; KANIA, DR; SCHOENBACH, KH; JOSHI, RP; MOLINA, C; BRINKMANN, RP
Abstract: 
+ Results Of Lifetime Testing Of Pulsed Power Switches Using An Electrolytic Capacitor Bank
  GIESSELMANN, M; LOREE, DL
Abstract: 
Publication Year:  1992
+ Spark Gap Igniter Studies On A Pulsed-Power Ignitron
  LOREE, D; GIESSELMANN, M; KRISTIANSEN, M
Abstract: 
Publication Year:  1991
+ Characterization And Study Of Light Degradation Effects In Ecr A-Si-H,Cl Films
  PALSULE, CP; GANGOPADHYAY, S; YOUNG, C; TROST, T; KRISTIANSEN, M
Abstract: 
+ Green Leaf Volatiles - A Ubiquitous Chemical Signal Modifies Insect Pheromone Responses
  DICKENS, JC; BILLINGS, RF; PAYNE, TL
Abstract: 
+ Novel Nitrogen-Containing Functional-Group Mimics Of Aldehyde Insect Sex-Pheromones
  UJVARY, I; DICKENS, JC
Abstract: 
+ Orientation To Host Plant And Conspecifics By The Boll-Weevil, Anthonomus-Grandis Boh (Coleoptera, Curculionidae) Electrophysiological And Behavioral Correlations
  DICKENS, JC
Abstract: 
Publication Year:  1990
+ Characterization Of A-Si-H,Cl And A-Sic-H Films Prepared By Electron-Cyclotron Resonance Plasma
  GANGOPADHYAY, S; TROST, T; KRISTIANSEN, M; YOUNG, C; ZHENG, P; PALSULE, C; PLEIL, M
Abstract: 
+ Surface Discharge Switch Design - The Critical Factor
  ENGEL, TG; KRISTIANSEN, M; BAKER, M; HATFIELD, LL
Abstract: 
+ Utilization Of A Thermal-Model To Predict Electrode Erosion Parameters Of Engineering Importance
  DONALDSON, AL; KRISTIANSEN, M
Abstract: