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Journal Publications

Publication Year:  2016
+ A 500 A device characterizer utilizing a pulsed-linear amplifier
  Lacouture, Shelby; Bayne, Stephen; ",A 500 A device characterizer utilizing a pulsed-linear amplifier,Review of Scientific Instruments,87,2,,2016,AIP
Abstract:  With the advent of modern power semiconductor switching elements, the envelope defining “high power” is an ever increasing quantity. Characterization of these semiconductor power devices generally falls into two categories: switching, or transient characteristics, and static, or DC characteristics. With the increasing native voltage and current levels that modern power devices are capable of handling, characterization equipment meant to extract quasi-static IV curves has not kept pace, often leaving researchers with no other option than to construct ad hoc curve tracers from disparate pieces of equipment. In this paper, a dedicated 10 V, 500 A curve tracer was designed and constructed for use with state of the art high power semiconductor switching and control elements. The characterizer is a physically small, pulsed power system at the heart of which is a relatively high power linear amplifier operating in a switched manner in order to deliver well defined square voltage pulses. These actively shaped pulses are used to obtain device’s quasi-static DC characteristics accurately without causing any damage to the device tested. Voltage and current waveforms from each pulse are recorded simultaneously by two separate high-speed analog to digital converters and averaged over a specified interval to obtain points in the reconstructed IV graph.

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+ Characteristics of a Four Element Gyromagnetic Nonlinear Transmission Line Array High Power Microwave Source
  J. Johnson, D. Reale, J. Krile, R. Garcia, W. Cravey, A. Neuber, J. Dickens, and J. Mankowski, "Characteristics of a Four Element Gyromagnetic Nonlinear Transmission Line Array High Power Microwave Source," Review of Scientific Instruments 87, 034706 (2016)
Abstract:  In this paper, a solid-state four element array gyromagnetic nonlinear transmission line high power microwave system is presented as well as a detailed description of its subsystems and general output capabilities. This frequency agile S-band source is easily adjusted from 2-4 GHz by way of a DC driven biasing magnetic field and is capable of generating electric fields of 7.8 kV/m at 10 m correlating to 4.2 MW of RF power with pulse repetition frequencies up to 1 kHz. Beam steering of the array at angles of ±16.7° is also demonstrated, and the associated general radiation pattern is detailed.

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+ Contact Extensions Over a High-k Dielectric Layer for Surface Electric Field Mitigation in High Power 4H-SiC Photoconductive Switches
  A. Chowdhury, D. Reale, R. P. Joshi, A. A. Neuber, and J. C. Dickens, "Contact Extensions Over a High-k Dielectric Layer for Surface Electric Field Mitigation in High Power 4H-SiC Photoconductive Switches." Accepted, 2016
Abstract:  We focus on a simulation study to probe the mitigation of electric fields, especially at the edges of metal contacts to SiC-based photoconductive switches. Field reduction becomes germane given that field-induced failures near contacts have been reported. A dual strategy of extending metal contacts to effectively spread the electric field over a larger distance and to employ HfO₂ as a high-k dielectric, is discussed. Simulation results show that peak electric fields can be lowered by up to ~67% relative to a standard design. Finally, our calculations predict that the internal temperature rise for a ~7-ns laser pulse and applied voltages around 20 kV (typical experimental values) would also be effectively controlled.

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+ Discrete Photon Implementation for Plasma Simulations
  A. Fierro, J. Stephens, S. Beeson, J. Dickens, and A. Neuber, "Discrete Photon Implementation for Plasma Simulations," Phys. Plasmas 23, 03506 (2016)
Abstract:  The self-produced light emission from pulsed plasma discharges and its impact on plasma development are challenging to characterize through simulation and modeling, chiefly due to the large number of radiating species and limited computer memory. Often, photo-processes, such as photo-ionization or photo-emission of electrons, are implemented through over-simplifying approximations or neglected altogether. Here, a method applicable to plasma simulations is implemented in a Particle-in-Cell /Monte Carlo Collision model, which is capable of discretely tracking photons and their corresponding wavelengths. Combined with the appropriate cross sections or quantum yields, a wavelength dependent model for photo-ionization or photo-emission may be implemented. Additionally, by resolving the wavelengths of each photon, an emission spectrum for a region of interest may be generated. Simulations for a pure nitrogen environment reveal that the calculated emission profile of the second positive system agrees well with the experimental spectrum of a pulsed, nanosecond discharge in the same spectral region.

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+ Failure Modes of 15-kV SiC SGTO Thyristors During Repetitive Extreme Pulsed Overcurrent Conditions
  J. A. Schrock et al., "Failure Modes of 15-kV SiC SGTO Thyristors During Repetitive Extreme Pulsed Overcurrent Conditions," in IEEE Transactions on Power Electronics, vol. 31, no. 12, pp. 8058-8062, Dec. 2016.
Abstract:  SiC SGTO thyristors are an advanced solution for increasing the power density of medium voltage power electronics. However, for these devices to replace Si thyristor technology in industrial applications their characteristics and failure modes must be understood. This letter presents the failure modes of two 15-kV SiC SGTO thyristors during repetitive overcurrent conditions. The devices were evaluated with 2-kA (3.85 kA/cm2) square pulses of 100 μs duration using a pulse forming network. Throughout testing, each devices' static characteristics were analyzed for signs of degradation; upon degradation, testing was ceased and the physical failure mode was determined through imaging with a scanning electron microscope (SEM) in conjunction with a focused ion beam. The electrical results demonstrate the failure modes of both SiC SGTO thyristors during pulsed overcurrents electrically manifested themselves as a conductive path through the gate-anode junction and an increased device on-state voltage. SEM imaging revealed one SiC thyristor formed an approximately 10-μm wide cylindrical void, and the second SiC thyristor formed an approximately 200-μm long crack. However, the experimental results demonstrate these 15-kV SiC SGTO thyristors' robust ability to repetitively switch at extreme high current density for tens of thousands of cycles.

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+ Investigation of a stripline transmission line structure for gyromagnetic nonlinear transmission line high power microwave sources
  D. V. Reale, J. M. Parson, A. A. Neuber, J. C. Dickens, and J. J. Mankowski, "Investigation of a stripline transmission line structure for gyromagnetic nonlinear transmission line high power microwave sources," Review of Scientific Instruments 87, 054704 (2016).
Abstract:  A stripline gyromagnetic nonlinear transmission line (NLTL) was constructed out of yttrium iron garnet ferrite and tested at charge voltages of 35 kV–55 kV with bias fields ranging from 10 kA/m to 20 kA/m. Typically, high power gyromagnetic NLTLs are constructed in a coaxial geometry. While this approach has many advantages, including a uniform transverse electromagnetic (TEM) mode, simple interconnection between components, and the ability to use oil or pressurized gas as an insulator, the coaxial implementation suffers from complexity of construction, especially when using a solid insulator. By moving to a simpler transmission line geometry, NLTLs can be constructed more easily and arrayed on a single substrate. This work represents a first step in exploring the suitability of various transmission line structures, such as microstrips and coplanar waveguides. The resulting high power microwave (HPM) source operates in ultra high frequency (UHF) band with an average bandwidth of 40.1% and peak rf power from 2 MW to 12.7 MW.

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+ Photoionization Capable, Extreme and Vacuum Ultraviolet Emission in Developing Low Temperature Plasmas in Air
  J. Stephens, A. Fierro, S. Beeson, G. Laity, D. Trienekens, R. P. Joshi, J. C. Dickens, and A. A. Neuber, "Photoionization Capable, Extreme and Vacuum Ultraviolet Emission in Developing Low Temperature Plasmas in Air." Plasma Sources Sci. Technol. 25 (2016) 025024 (11pp)
Abstract:  Not Available

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Publication Year:  2015
+ A Frequency Stable Vacuum-Sealed Tube High-Power Microwave Vircator Operated at 500 Hz
  J. M. Parson, C. F. Lynn, M. C. Scott, S. Calico, J. C. Dickens, A. A. Neuber, and J. J. Mankowski, "A Frequency Stable Vacuum-Sealed Tube High-Power Microwave Vircator Operated at 500 Hz," Electron Device Letters, (2015).
Abstract:  Operation of repetitive high-power microwave (HPM) sources is predominantly limited by thermal properties of anode and cathode materials. This paper presents a reflex-triode virtual cathode oscillator (vircator) capable of operating at 500 Hz at current densities between 100-200 A/cm2 for multiple burst durations of 1-2 seconds. Stable vircator operation under such a thermally punishing environment is facilitated by the use of a thin pyrolytic graphite anode. The results presented focus on two anode-cathode (A-K) gap spacings: 11 mm and 21 mm, which produce stable microwave radiation at 4.6 GHz and 1.6 GHz, respectively. Characteristic voltage, current and microwave waveforms in conjunction with short-time Fourier transforms (STFTs), frequency spectrographs and HPM power density data for 1,000 and 500 pulses at 1.6 GHz and 4.6 GHz, respectively, are presented.

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+ A high power microwave triggered RF opening switch
  S. Beeson, J. Dickens, A. Neuber, "A high power microwave triggered RF opening switch", Rev. Sci. Instrum., (2015).
Abstract:  A 4-port S-band waveguide structure was designed and fabricated such that a signal of any amplitude (less than 1 MW) can be switched from a normally closed state, <0.5 dB insertion loss (IL), to an open state >30 dB IL by initiating plasma in a gas cell situated at the junction of this waveguide and one propagating a megawatt level magnetron pulse. The 90/10 switching time is as low as 20 ns with a delay of ∼30 ns between the onset of the high power microwave pulse and the initial drop of the signal. Two ports of this device are for the high power triggering pulse while the other two ports are for the triggered signal in a Moreno-like coupler configuration. In order to maintain high isolation, these two sets of waveguides are rotated 90° from each other with a TE111 resonator/plasma cell located at the intersection. This manuscript describes the design and optimization of this structure using COMSOL 4.4 at the design frequency of 2.85 GHz, comparison of simulated scattering parameters with measured "cold tests" (testing without plasma), and finally the temporal waveforms of this device being used to successfully switch a low power CW signal from 2 W to <5 mW on a sub-microsecond timescale.

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+ A Model Study of the Role of Workfunction Variations in Cold Field Emission From Microstructures With Inclusion of Field Enhancements
  H. Qiu, R. P. Joshi, A. Neuber, and J. Dickens, "A Model Study of the Role of Workfunction Variations in Cold Field Emission From Microstructures With Inclusion of Field Enhancements," Semicond. Sci. Technol. 30, 105038 (2015).
Abstract:  An analytical study of field emission from microstructures is presented that includes position-dependent electric field enhancements, quantum corrections due to electron confinement and fluctuations of the workfunction. Our calculations, applied to a ridge microstructure, predict strong field enhancements. Though quantization lowers current densities as compared to the traditional Fowler–Nordheim process, strong field emission currents can nonetheless be expected for large emitter aspect ratios. Workfunction variations arising from changes in electric field penetration at the surface, or due to interface defects or localized screening, are shown to be important in enhancing the emission currents.

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+ Analysis of high field effects on the steady-state current-voltage response of semi-insulating 4H-SiC for photoconductive switch applications
  R. Tiskumara, R. P. Joshi, D. Mauch, J. C. Dickens, and A. A. Neuber, "Analysis of high field effects on the steady-state current-voltage response of semi-insulating 4H-SiC for photoconductive switch applications," J. Appl. Phys. 118, 095701 (2015)
Abstract:  A model-based analysis of the steady-state, current-voltage response of semi-insulating 4H-SiC is carried out to probe the internal mechanisms, focusing on electric field driven effects. Relevant physical processes, such as multiple defects, repulsive potential barriers to electron trapping, band-to-trap impact ionization, and field-dependent detrapping, are comprehensively included. Results of our model match the available experimental data fairly well over orders of magnitude variation in the current density. A number of important parameters are also extracted in the process through comparisons with available data. Finally, based on our analysis, the possible presence of holes in the samples can be discounted up to applied fields as high as ∼275 kV/cm.

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+ Anode Materials for High-Average-Power Operation in Vacuum at Gigawatt Instantaneous Power Levels
  Curtis F Lynn, Jonathan M. Parson, Michael C. Scott, Steve E. Calico, James C. Dickens, Andreas A. Neuber, and John J. Mankowski. "Anode Materials for High-Average-Power Operation in Vacuum at Gigawatt Instantaneous Power Levels." Electron Devices, IEEE Transactions on 62, no. 6 2044-2047 (2015)
Abstract:  The thermal behavior of several electrically conducting solids under high incident electron fluence in high vacuum was evaluated. At electron energies of up to ~200 keV, the depth-dose relationship for electron penetration into the materials was considered, and the resulting energy deposition profile from the surface was revealed to extend to a maximum of ~175 μm below the surface depending on the anode material. Black body radiation is considered as the major mechanism that balances the power deposited in the material on the timescales of interest. Comparing the radiated power density at the sublimation temperature for different materials, metallic/nonmetallic, revealed that pyrolytic graphite anodes may radiate over 20 times more power than metallic anodes before failure due to sublimation. In addition, transparent pyrolytic graphite anodes (with a thickness on the order of several tens of micrometer) potentially radiate up to 40 times that of metallic anodes, since heating by the electron beam is approximately uniform throughout the thickness of the material, thus radiation is emitted from both sides. Experimental results obtained from titanium and pyrolytic graphite anodes validate the thermal analysis.

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+ Development and testing of an active high voltage saturation probe for characterization of ultra-high voltage silicon carbide semiconductor devices
  Bilbao, Argenis V.; Schrock, James A.; Ray, William B.; Kelley, Mitchell D.; Holt, Shad L.; Giesselmann, Michael G.; Bayne, Stephen B., Development and testing of an active high voltage saturation probe for characterization of ultra-high voltage silicon carbide semiconductor devices, Review of Scientific Instruments, 86, 085104 (2015)
Abstract:  Obtaining accurate collector to emitter voltage measurements when characterizing high voltage silicon carbide (SiC) devices requires the ability to measure voltages in the range of zero to 10 V while the device is in the on-state and the ability to withstand ultra-high voltages while the device is in the off-state. This paper presents a specialized voltage probe capable of accurately measuring the aforementioned range. A comparison is made between the proposed probe and other commonly used high voltage probe alternatives in relation to high voltage SiC device testing. Testing of the probe was performed to ensure linearity, high accuracy, and high bandwidth.

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+ Digital control of a rapid capacitor charger with sensor-less voltage feedback
  M. G. Giesselmann and A. Bilbao, "Digital control of a rapid capacitor charger with sensor-less voltage feedback," in IEEE Transactions on Dielectrics and Electrical Insulation, vol. 22, no. 4, pp. 1930-1936, August 2015.
Abstract:  This paper describes the implementation of a load voltage observer into the control algorithms of a Rapid Capacitor Charger controlled by a digital signal controller (DSC) with a fast DSP core. A hybrid peak current mode control algorithm with digital control of the PWM signal and high speed analog current sensing is used to control the inverter of the charger. The DSC controller keeps the current loop stable using adaptive slope compensation. In addition to providing fast adaptive digital control of the current loop, the DSC can perform additional functions such as estimation of the voltage level of the load capacitor. This avoids the cost, bandwidth limitations and insulation challenges of a conventional HV-sensor. To evaluate the performance of the load voltage observer, we measured the output voltage with a laboratory grade HV probe to establish a reference to test the results of the digital algorithm.

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+ Evaluating the Performance of a Carbon-Epoxy Capillary Cathode and Carbon Fiber Cathode in a Sealed-Tube Vircator Under UHV Conditions
  E. Rocha, P. M. Kelly, J. M. Parson, C. F. Lynn, J. C. Dickens, A. A. Neuber, J. J. Mankowski, T. Queller, J. Gleizer, and Y. E. Krasik. "Evaluating the Performance of a Carbon-Epoxy Capillary Cathode and Carbon Fiber Cathode in a Sealed-Tube Vircator Under UHV Conditions." IEEE Trans. on Plasma Sci. 43, 2670-2675 (2015)
Abstract:  This paper evaluates the performance of a bimodal carbon fiber cathode and a carbon-epoxy multicapillary cathode operating within a reflex-triode sealed-tube virtual cathode oscillator (vircator). The experimental results reveal that both cathodes exhibit similar emission behavior, although with some significant operational differences. An eight-stage 84-J pulseforming network-based Marx generator serves to drive both cathodes at 250 kV and 3-4 kA with a ~70-ns pulsewidth. Both cathodes undergo conditioning over 10000 pulses to determine gas evolution as well as electrical changes over time. Gas evolution of both cathodes is observed using a residual gas analyzer to determine individual gas constituents. A comparison of diode voltage, diode current, RF output, and outgassing data for both cathodes during vircator operation over 10000 pulses is presented to quantify cathode performance in a sealed-tube vircator. Changes in cathode surface morphology, from virgin to postmortem, are discussed. Data for various anode-cathode gap distances, from 3 to 15 mm, are presented. The evolution of voltage and current inputs to the vircator is discussed.

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+ Evaluation of a Pulsed Ultraviolet Light-Emitting Diode for Triggering Photoconductive Semiconductor Switches
  D. Mauch, C. Hettler, W. W. Sullivan, A. A. Neuber, and J, Dickens, "Evaluation of a Pulsed Ultraviolet Light-Emitting Diode for Triggering Photoconductive Semiconductor Switches," IEEE Trans. Plasma Sci. 43, 2182-2186 (2015)
Abstract:  The power output, forward voltage, conversion efficiency, and spectral characteristics of a 365 nm ultraviolet light-emitting diode (LED) were measured for applications of triggering wide-bandgap photoconductive switches for pulsed power applications. Pulsed currents through the LED ranged from 125 mA up to 2.2 A at widths from 10 μs up to several seconds. Using time-resolved electroluminescence spectroscopy, peak emission was observed to occur at 368.5 nm for short pulses with a red-shift to 371.8 nm for pulses 8 s in duration. A peak light output of 4.1 W was measured for short pulses (<;50 μs) of 2.12 A, corresponding to six times the rated output specification. The LED was used to trigger a high-voltage photoconductive semiconductor switch (PCSS) at voltages up to 6 kV into a high-impedance load. The 365 nm LED is a promising candidate for optical triggering of PCSS devices.

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+ Failure Analysis of 1200-V/150-A SiC MOSFET Under Repetitive Pulsed Overcurrent Conditions
  J. A. Schrock et al., "Failure Analysis of 1200-V/150-A SiC MOSFET Under Repetitive Pulsed Overcurrent Conditions," in IEEE Transactions on Power Electronics, vol. 31, no. 3, pp. 1816-1821, March 2016.
Abstract:  SiC MOSFETs are a leading option for increasing the power density of power electronics; however, for these devices to supersede the Si insulated-gate bipolar transistor, their characteristics have to be further understood. Two SiC vertically oriented planar gate D-MOSFETs rated for 1200 V/150 A were repetitively subjected to pulsed overcurrent conditions to evaluate their failure mode due to this common source of electrical stress. This research supplements recent work that demonstrated the long term reliability of these same devices [1]. Using an RLC pulse-ring-down test bed, these devices hard-switched 600 A peak current pulses, corresponding to a current density of 1500 A/cm2. Throughout testing, static characteristics of the devices such as BVDSS, RDS (on), and VGS(th) were measured with a high power device analyzer. The experimental results indicated that a conductive path was formed through the gate oxide; TCAD simulations revealed localized heating at the SiC/SiO2 interface as a result of the extreme high current density present in the device's JFET region. However, the high peak currents and repetition rates required to produce the conductive path through the gate oxide demonstrate the robustness of SiC MOSFETs under the pulsed overcurrent conditions common in power electronic applications.

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+ Heating Based Model Analysis for Explosive Emission Initiation at Metal Cathodes
  A. Majzoobi, R. P. Joshi, A. A. Neuber, and J. C. Dickens, "Heating Based Model Analysis for Explosive Emission Initiation at Metal Cathodes," AIP Advances 5, 127237, 2015.
Abstract:  This contribution presents a model analysis for the initiation of explosive emission; a phenomena that is observed at cathodesurfaces under high current densities. Here, localized heating is quantitatively evaluated on ultrashort time scales as a potential mechanism that initiates explosive emission, based on a two-temperature, relaxation time model. Our calculations demonstrate a strong production of nonequilibrium phonons, ultimately leading to localized melting. Temperatures are predicted to reach the cathode melting point over nanosecond times within the first few monolayers of the protrusion. This result is in keeping with the temporal scales observed experimentally for the initiation of explosive emission.

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+ High Power Lateral Silicon Carbide Photoconductive Semiconductor Switches and Investigation of Degradation Mechanisms
  D. Mauch, W. Sullivan III, A. Bullick, A. Neuber, J. Dickens, "High Power Lateral Silicon Carbide Photoconductive Semiconductor Switches and Investigation of Degradation Mechanisms," IEEE Trans. Plasma Sci. 43, 2021-2031, 2015.
Abstract:  Several generations of high power, lateral, linear mode, intrinsically triggered 4H-SiC photoconductive semiconductor switch designs and their performance are presented. These switches were fabricated from high purity semi-insulating 4H-SiC samples measuring 12.7 mm × 12.7 mm × 0.36 mm and were able to block dc electric fields up to 370 kV/cm with leakage currents less than 10 μA without failure. Switching voltages and current s up to 26 kV and 450 A were achieved with these devices and ON-state resistances of 2 Ω were achieved with 1 mJ of 355 nm laser energy (7 ns FWHM). After fewer than 100 high power switching cycles, these devices exhibited cracks near the metal/SiC interface. Experimental and simulation results investigating the root cause of this failure mechanism are also presented. These results strongly suggest that a transient spike in the magnitude of the electric field at the metal/SiC interface during both switch closing and opening is the dominant cause of the observed cracking.

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+ High-Mobility Stable 1200-V, 150-A 4H-SiC DMOSFET Long-Term Reliability Analysis Under High Current Density Transient Condition
  J. A. Schrock et al., "High-Mobility Stable 1200-V, 150-A 4H-SiC DMOSFET Long-Term Reliability Analysis Under High Current Density Transient Conditions," in IEEE Transactions on Power Electronics, vol. 30, no. 6, pp. 2891-2895, June 2015.
Abstract:  For SiC DMOSFETs to obtain widespread usage in power electronics their long-term operational ability to handle the stressful transient current and high temperatures common in power electronics needs to be further verified. To determine the long-term reliability of a single 4H-SiC DMOSFET, the effects of extreme high current density were evaluated. The 4H-SiC DMOSFET has an active conducting area of 40 mm2, and is rated for 1200 V and 150 A. The device was electrically stressed by hards-witching transient currents in excess of four times the given rating (>600 A) corresponding to a current density of 1500 A/cm2. Periodically throughout testing, several device characteristics including RDS(on) and VG S(th) were measured. After 500 000 switching cycles, the device showed a 6.77% decrease in RDS (on), and only a 132-mV decreased in VG S(th). Additionally, the dc characteristics of the device were analyzed from 25 to 150 °C and revealed a 200-mV increase in on-state voltage drop at 20 A and a 2-V reduction in VG S(th) at 150 °C. These results show this SiC DMOSFET has robust long-term reliability in high-power applications that are susceptible to pulse over currents, such as pulsed power modulators and hard-switched power electronics.

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+ Material selection of a ferrimagnetic loaded coaxial delay line for phasing gyromagnetic nonlinear transmission lines
  J. M. Johnson, D. V. Reale, W. H. Cravey, R. S. Garcia, D. H. Barnett, A. A. Neuber, J. C. Dickens, and J. J. Mankowski. "Material selection of a ferrimagnetic loaded coaxial delay line for phasing gyromagnetic nonlinear transmission lines." Review of Scientific Instruments 86, 8, 084702 (2015)
Abstract:  Implementing nonlinear transmission line (NLTL) technology in the design of a high power microwave source has the benefits of producing a comparatively small and lightweight solid-state system where the emission frequency is easily tuned. Usually, smaller in physical size, single NLTLs may produce significantly less power than its vacuum based counterparts. However, combining individual NLTL outputs electrically or in free-space is an attractive solution to achieve greater output power. This paper discusses a method for aligning a four element NLTL antenna array with coaxial geometry using easily adjustable temporal delay lines. These delay lines, sometimes referred to as pulse shock lines or pulse sharpening lines, are placed serially in front of the main NLTL line. The propagation velocity in each delay line is set by the voltage amplitude of an incident pulse as well as the magnetic field bias. Each is adjustable although for the system described in this paper, the voltage is held constant while the bias is changed through applying an external DC magnetic field of varying magnitude. Three different ferrimagnetic materials are placed in the temporal delay line to evaluate which yields the greatest range of electrical delay with the least amount of variability from consecutive shots.

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+ Multipactor threshold calculation of coaxial transmission lines in microwave applications with nonstationary statistical theory
  S. Lin, H. Wang, Y. Li, C. Liu, N. Zhang, W. Cui and A. Neuber, "Multipactor threshold calculation of coaxial transmission lines in microwave applications with nonstationary statistical theory," Phys. Plasmas 22, 082114 (2015)
Abstract:  This paper presents a statistical theory for the initial onset of multipactor breakdown in coaxial transmission lines, taking both the nonuniform electric field and random electron emission velocity into account. A general numerical method is first developed to construct the joint probability density function based on the approximate equation of the electron trajectory. The nonstationary dynamics of the multipactor process on both surfaces of coaxial lines are modelled based on the probability of various impacts and their corresponding secondary emission. The resonant assumption of the classical theory on the independent double-sided and single-sided impacts is replaced by the consideration of their interaction. As a result, the time evolutions of the electron population for exponential growth and absorption on both inner and outer conductor, in response to the applied voltage above and below the multipactor breakdown level, are obtained to investigate the exact mechanism of multipactor discharge in coaxial lines. Furthermore, the multipactor threshold predictions of the presented model are compared with experimental results using measured secondary emission yield of the tested samples which shows reasonable agreement. Finally, the detailed impact scenario reveals that single-surface multipactor is more likely to occur with a higher outer to inner conductor radius ratio.

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+ Optically isolated, 2 kHz repetition rate, 4 kV solid-state pulse trigger generator
  D. H. Barnett, J. M. Parson, C. F. Lynn, P. M. Kelly, M. Taylor, S. Calico, M. C. Scott, J. C. Dickens, A. A. Neuber, and J. J. Mankowski, "Optically isolated, 2 kHz repetition rate, 4 kV solid-state pulse trigger generator," Rev. Sci. Instrum. 86, 034702 (2015).
Abstract:  This paper presents the design and operation characteristics of a solid-state high voltage pulse generator. Its primary utilization is aimed at triggering a gaseous spark gap with high repeatability. Specifically, the trigger generator is designed to achieve a risetime on the order of 0.1 kV/ns to trigger the first stage, trigatron spark gap of a 10-stage, 500 kV Marx generator. The major design components are comprised of a 60 W constant current DC-DC converter for high voltage charging, a single 4 kV thyristor, a step-up pulse transformer, and magnetic switch for pulse steepening. A risetime of <30 ns and pulse magnitude of 4 kV is achieved matching the simulated performance of the design.

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+ Optimizing drive parameters of a nanosecond, repetitively pulsed microdischarge high power 121.6 nm source
  J. Stephens, A. Fierro, D. Trienekens, J. Dickens, and A. Neuber, "Optimizing drive parameters of a nanosecond, repetitively pulsed microdischarge high power 121.6 nm source," Plasma Sources Science and Technology 24, 015013 (6pp) (2015).
Abstract:  Utilizing nanosecond high voltage pulses to drive microdischarges (MDs) at repetition rates in the vicinity of 1 MHz previously enabled increased time-averaged power deposition, peak vacuum ultraviolet (VUV) power yield, as well as time-averaged VUV power yield. Here, various pulse widths (30-250 ns), and pulse repetition rates (100 kHz-5 MHz) are utilized, and the resulting VUV yield is reported. It was observed that the use of a 50 ns pulse width, at a repetition rate of 100 kHz, provided 62 W peak VUV power and 310 mW time-averaged VUV power, with a time-averaged VUV generation efficiency of ~1.1%. Optimization of the driving parameters resulted in 1-2 orders of magnitude increase in peak and time-averaged power when compared to low power, dc-driven MDs.

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+ Particle-in-Cell Based Parameter Study of 12-Cavity, 12-Cathode Rising-Sun Relativistic Magnetrons for Improved Performance
  A. Majzoobi, R. P. Joshi, A. A. Neuber, and J. C. Dickens, "Particle-in-Cell Based Parameter Study of 12-Cavity, 12-Cathode Rising-Sun Relativistic Magnetrons for Improved Performance," AIP Advances 5, 107102 (2015).
Abstract:  Particle-in-cell simulations are performed to analyze the efficiency, output power and leakage currents in a 12-Cavity, 12-Cathode rising-sun magnetron with diffraction output (MDO). The central goal is to conduct a parameter study of a rising-sun magnetron that comprehensively incorporates performance enhancing features such as transparent cathodes, axial extraction, the use of endcaps, and cathode extensions. Our optimum results demonstrate peak output power of about 2.1 GW, with efficiencies of ∼70% and low leakage currents at a magnetic field of 0.45 Tesla, a 400 kV bias with a single endcap, for a range of cathode extensions between 3 and 6 centimeters.

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+ Robert Barker Memorial Session: Leadership in Plasma Science and Applications
  K. Becker, Kurt, B. Godfrey, E. Kunhardt, M. Laroussi, L. Ludeking, A. Neuber, E. Schamiloglu, A. Woods, Robert Barker Memorial Session: Leadership in Plasma Science and Applications," to be published in IEEE Trans Plasma Sci (2015).
Abstract:  This paper summarizes the Dr. Robert J. Barker memorial session at the IEEE International Conference on Plasma Science 2014. Each section summarizes progress in a plasma research area strongly influenced by Dr. Barker's leadership: 1) plasma medicine; 2) atmospheric-pressure plasmas; 3) high-power microwaves; 4) pulsed power; and 5) numerical simulation of plasmas. He had a profound influence on these and other plasma science applications, as well as on numerous individual researchers. He will be missed greatly.

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+ Self-Induced Gaseous Plasma as HPM Opening Switch Medium
  S. Lin, S. Beeson, C. Liu, J. Dickens, A. Neuber, "Self-Induced Gaseous Plasma as HPM Opening Switch Medium," Phys. Plasmas 22, 043509 (2015)
Abstract:  Self-induced gaseous plasma is evaluated as active opening switch medium for pulsed high power microwave radiation. The self-induced plasma switch is investigated for N2 and Ar environments under pressure conditions ranging from 25 to 700 Torr. A multi-pass TE111 resonator is used to significantly reduce the delay time inherently associated with plasma generation. The plasma forms under the pulsed excitation of a 4 MW magnetron inside the central dielectric tube of the resonator, which isolates the inner atmospheric gas from the outer vacuum environment. The path from the power source to the load is designed such that the pulse passes through the plasma twice with a 35 ns delay between these two passes. In the first pass, initial plasma density is generated, while the second affects the transition to a highly reflective state with as much as 30 dB attenuation. Experimental data revealed that virtually zero delay time may be achieved for N2 at 25 Torr. A two-dimensional fluid model was developed to study the plasma formation times for comparison with experimental data. The delay time predicted from this model agrees well with the experimental values in the lower pressure regime (error < 25%), however, due to filamentary plasma formation at higher pressures, simulated delay times may be underestimated by as much as 50%.

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+ Time-discretized Extreme and Vacuum Ultraviolet Spectroscopy of Spark Discharges in Air, N2 and O2
  D. Trienekens, J. Stephens, A. Fierro, J. Dickens, and A. Neuber "Time-discretized Extreme and Vacuum Ultraviolet Spectroscopy of Spark Discharges in Air, N2 and O2," Journal of Physics D: Applied Physics 49, 3, (2015).
Abstract:  In this paper we present time-discretized spectra of spark discharges in air, N2 and O2. In previous work, a system for temporally resolved spectral analysis of extreme ultraviolet (EUV) and vacuum ultraviolet (VUV) emission from spark discharges was presented, along with some initial results. As was noted in this paper, statistical variances and the lacking of an apparatus sensitivity profile limited the usability of the data obtained. We have investigated the cause of these variances and improved the setup to reduce their effect. We also investigated the apparatus sensitivity profile to correct the intensity of measured lines. Newly obtained spectra in dry air, N2 and O2 are presented. Air and N2 show high emission in the vicinity of 100 nm, where direct photoionization of molecular oxygen is possible, in the first 250 ns of the discharge. We conclude this emission originates from nitrogen, which has several intense molecular transitions in this region. This finding is confirmed by our experimental results which show the emission in this region is much lower in oxygen.

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Publication Year:  2014
+ 3-D Simulation of Low-Temperature Plasma Development Under Pulsed Conditions
  A. Fierro, J. Dickens, A. Neuber, "3-D Simulation of Low-Temperature Plasma Development Under Pulsed Conditions," IEEE Transactions on Plasma Science 42, 2864-2865, (2014).
Abstract:  The development of a low-temperature plasma in a needle-protrusion to plane gap is investigated utilizing a 3-D particle-in-cell/Monte Carlo collision method implemented to run on single NVIDIA graphics processing unit. In addition to electron collisions, the model includes field detachment, photon tracking, and a drift-diffusion approximation for positive ions. The simulated geometry tracks several million electrons with 15-μm spatial resolution.

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+ A Passive Measurement of Dissociated Atom Densities in Atmospheric Pressure Air Discharge Plasmas using Vacuum Ultraviolet Self-Absorption Spectroscopy
  G. Laity, A. Fierro, J Dickens, A Neuber, "A Passive Measurement of Dissociated Atom Densities in Atmospheric Pressure Air Discharge Plasmas using Vacuum Ultraviolet Self-Absorption Spectroscopy," Journal of Applied Physics 115, 123302, (2014).
Abstract:  We demonstrate a method for determining the dissociation degree of atmospheric pressure air discharges by measuring the self-absorption characteristics of vacuum ultraviolet radiation from O and N atoms in the plasma. The atom densities are determined by modeling the amount of radiation trapping present in the discharge, without the use of typical optical absorption diagnostic techniques which require external sources of probing radiation into the experiment. For an 8.0 mm spark discharge between needle electrodes at atmospheric pressure, typical peak O atom densities of 8.5e17 1/cm3 and peak N atom densities of 9.9e17 1/cm are observed within the first ∼1.0 mm of plasma near the anode tip by analyzing the OI and NI transitions in the 130.0-132.0 nm band of the vacuum ultraviolet spectrum.

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+ An evaluation system for experimental silicon and silicon carbide super gate turn off thyristors
  Bayne, Stephen; Lacouture, Shelby; Lawson, Kevin; Giesselmann, Michael; Scozzie, Charles J; O’Brien, Heather; Ogunniyi, Aderinto A; ",An evaluation system for experimental silicon and silicon carbide super gate turn off thyristors,Review of Scientific Instruments,85,7,075107,2014,AIP Publishing
Abstract:  This paper describes the design and implementation of a small-scale pulsed power system specifically intended to evaluate the suitability of experimental silicon and silicon carbide high power Super Gate Turn Off thyristors for high action (500 A2 s and above) pulsed power applications where energy is extracted from a storage element in a rapid and controlled manner. To this end, six of each type of device was placed in a controlled three phase rectifier circuit which was in turn connected to an aircraft ground power motor-generator set and subjected to testing protocols with varying power levels, while parameters such as offset firing angle were varied.

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+ Bias-field controlled phasing and power combination of gyromagnetic nonlinear transmission lines
  D. V. Reale, J.-W. B. Bragg, N. R. Gonsalves, J. M. Johnson, A. A. Neuber, J. C. Dickens, and J. J. Mankowski, "Bias-field controlled phasing and power combination of gyromagnetic nonlinear transmission lines," Review of Scientific Instruments, 85, 054706 (2014).
Abstract:  Gyromagnetic Nonlinear Transmission Lines (NLTLs) generate microwaves through the damped gyromagnetic precession of the magnetic moments in ferrimagnetic material, and are thus utilized as compact, solid-state, frequency agile, high power microwave (HPM) sources. The output frequency of a NLTL can be adjusted by control of the externally applied bias field and incident voltage pulse without physical alteration to the structure of the device. This property provides a frequency tuning capability not seen in many conventional e-beam based HPM sources. The NLTLs developed and tested are mesoband sources capable of generating MW power levels in the L, S, and C bands of the microwave spectrum. For an individual NLTL the output power at a given frequency is determined by several factors including the intrinsic properties of the ferrimagnetic material and the transmission line structure. Hence, if higher power levels are to be achieved, it is necessary to combine the outputs of multiple NLTLs. This can be accomplished in free space using antennas or in a transmission line via a power combiner. Using a bias-field controlled delay, a transient, high voltage, coaxial, three port, power combiner was designed and tested. Experimental results are compared with the results of a transient COMSOL simulation to evaluate combiner performance.

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+ Conditioning of carbon fiber cathodes in UHV-sealed tubes at 200 A/cm²
  J. Parson, C. Lynn, J. Mankowski, M. Kristiansen, A. Neuber, J. Dickens, "Conditioning of carbon fiber cathodes in UHV-sealed tubes at 200 A/cm²," IEEE Trans. On Plasma Sci. 42, 2007-2014 (2014).
Abstract:  This paper presents a study on outgassing and electrical conditioning for three carbon fiber cathode types in a vacuum-sealed, high-power microwave virtual-cathode-oscillator (vircator) that operates in the low 1e-9 torr pressure regime. The three cathode types consist of a bare bimodal fiber structure, a bare unimodal fiber structure, and a cesium-iodide coated bimodal fiber structure with identical fiber coverage of 2% by area with a surface area of ~20 cm2. The electrodes are cleaned by a 1.2 kW, argon/oxygen microwave plasma prior to complete vircator assembly, followed by a 300 °C bake-out for 72 h. Each cathode was pulsed in a single pulse operation by an 80 J, low inductance Marx generator with an approximate pulsewidth of 100 ns full-width at half-maximum for 10000 current pulses. The data presented includes individual gas constituents, high-speed intensified charge coupled device (ICCD) imaging, and voltage and current waveforms. The conditioning process resulted in a gas load reduction of ~80% overall, with the indication that the bare bimodal fiber structure performed the best as diode power increased throughout the experiment, while the power decreased for the other tested cathode types.

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+ Emission Behavior of Three Conditioned Carbon Fiber Cathode Types in UHV-Sealed Tubes at 200 A/cm²
  J. Parson, C. Lynn, J. Mankowski, A. Neuber, and J. Dickens, "Emission Behavior of Three Conditioned Carbon Fiber Cathode Types in UHV-Sealed Tubes at 200 A/cm²," IEEE Trans. on Plasma Sci. 42, 3982 - 3988 (2014).
Abstract:  When subjected to high electric fields in vacuum, carbon fiber cathodes produce intense electron beams suitable for high-power microwave (HPM) generation at very high current densities. However, the production mechanisms of these intense electron beams are not fully understood. This paper presents the postmortem examination of three conditioned carbon fiber cathode types. The three cathode types consist of an uncoated, bare unimodal fiber structure, a bare bimodal fiber structure, and a cesium-iodide (CsI)-coated bimodal fiber structure, all with identical fiber coverage of 2% by area. Each cathode was conditioned prior to testing by single pulse operation driven by an 80 J Marx generator for 10 000 pulses. HPM, voltage, and current waveforms of each cathode are presented. The bare bimodal cathode radiated more microwave power than the CsI-coated cathode and bare unimodal cathode. Scanning electron microscopy imagery presents evidence of two emission mechanisms: 1) explosive electron emission and 2) surface flashover, which both were found on the CsI-coated cathode. In addition, no evidence of surface flashover was found on either uncoated cathode.

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+ Global Model for Total Delay Time Distribution of High Power Microwave Surface Flashover,
  S. Beeson, J. Dickens, and A. Neuber, "Global Model for Total Delay Time Distribution of High Power Microwave Surface Flashover," IEEE Trans. On Plasma Sci. 42, 3450-3457 (2014).
Abstract:  A global model of high-power microwave (HPM) window breakdown is elucidated. The model provides a practical approach for estimating the maximum microwave power and pulse length that can be transmitted for a given window geometry at varying background gas pressure. Based on recent experimental and modeling progress, the formative and statistical breakdown delay time contributions are included in the model. The provided details are intended to give the reader a starting point in designing an HPM system for which surface breakdown along the output window is a major concern. Spanning five orders of magnitude in power, four microwave bands, three orders of magnitude in pulsewidth, three orders of magnitude in pressure, and three different gas types, the model serves to determine the probability of breakdown for a given set of input parameters with the modest computational effort. Examples of how to use the model are given, and the results are compared with actual systems and measured experimental delay times.

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+ Graphics processing unit accelerated three-dimensional model for the simulation of pulsed low-temperature plasmas
  A. Fierro, J. Dickens, and A. Neuber, "Graphics processing unit accelerated three-dimensional model for the simulation of pulsed low-temperature plasmas," Physics of Plasmas 21, 123504 (2014).
Abstract:  A 3-dimensional particle-in-cell/Monte Carlo collision simulation that is fully implemented on a graphics processing unit (GPU) is described and used to determine low-temperature plasma characteristics at high reduced electric field, E/n, in nitrogen gas. Details of implementation on the GPU using the NVIDIA Compute Unified Device Architecture framework are discussed with respect to efficient code execution. The software is capable of tracking around 10e6 particles with dynamic weighting and a total mesh size larger than 1e8 cells. Verification of the simulation is performed by comparing the electron energy distribution function and plasma transport parameters to known Boltzmann Equation (BE) solvers. Under the assumption of a uniform electric field and neglecting the build-up of positive ion space charge, the simulation agrees well with the BE solvers. The model is utilized to calculate plasma characteristics of a pulsed, parallel plate discharge. A photoionization model provides the simulation with additional electrons after the initial seeded electron density has drifted towards the anode. Comparison of the performance benefits between the GPU-implementation versus a CPU-implementation is considered, and a speed-up factor of 13 for a 3D relaxation Poisson solver is obtained. Furthermore, a factor 60 speed-up is realized for parallelization of the electron processes.

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+ Imaging of Explosive Emission Cathode and Anode Plasma in a Vacuum-Sealed Vircator High-Power Microwave Source at 250 A/cm²
  J. Parson, J. Mankowski, J. Dickens, A. Neuber, "Imaging of Explosive Emission Cathode and Anode Plasma in a Vacuum-Sealed Vircator High-Power Microwave Source at 250 A/cm²," IEEE Trans. On Plasma Sci. 42, 2592 - 2593 (2014).
Abstract:  Cold cathode operation under high current densities leads to explosive electron emission (EEE) that contributes to early A-K gap closure. Hence, inconsistent vacuum conditions and, if utilized in a high power microwave device, degradation of microwave output power are observed. The EEE centers are known to produce localized plasmas on the surface of the cathode that release and ionize the electrode material. Further, low melting point material in the anode is released due to electron bombardment accompanied by a significant surface temperature increase. Postmortem analysis has revealed particles up to 50 μm in diameter embedded in the opposite electrode. High speed ICCD imaging during A-K gap operation enabled resolving the plasma's spatial characteristics in time. Images of cathode and anode plasma during the operation of a virtual cathode oscillator at 250 A/cm2 under ultrahigh vacuum conditions are presented.

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+ Influence of VUV illumination on breakdown mechanics: pre-ionization, direct photoionization, and discharge initiation
  J Stephens, A Fierro, J Dickens, and A Neuber, "Influence of VUV illumination on breakdown mechanics: pre-ionization, direct photoionization, and discharge initiation," Journal of Physics D: Applied Physics 47 (32), 325501 (2014).
Abstract:  A microdischarge (MD) vacuum ultraviolet (VUV) light source is fired onto a N2-NO (99.92 : 0.08%) target gas. The minor gas constituent, NO, was chosen for its ionization potential (9.23 eV) and photoionization cross-section (1.4e−18 cm2) at the wavelength of interest (121.6 nm, 10.2 eV). The result is a plasma generated entirely by volume photoionization in a N2-NO background. Using a very low electric field amplitude, charge carriers are drifted though the photoplasma at picoampere levels, serving as a non-invasive diagnostic. Using a simple one-dimensional fluid approximation for the low electric field condition, theoretical predictions of photoplasma current were found to be in meaningful agreement with experimental data. The impact of direct photoionization and pre-ionization on nanosecond timescale high voltage breakdown yielded two primary observations: (1) a significant reduction in the formative delay time necessary for spark formation, and (2) almost complete elimination of the statistical delay time. Again utilizing one-dimensional fluid approximations, reasonable agreement between experimental and simulated breakdown voltage was observed. Utilizing the same VUV source to illuminate a HV spark gap biased to about 95% self-breakdown voltage revealed that direct volume photoionization alone was insufficient to trigger breakdown of the high voltage gap. However, permitting electrode illumination, the same source was found to be capable of triggering breakdown in the undervoltaged gap, albeit with a large temporal jitter.

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+ Micrometer-resolution high speed imaging of pulsed microdischarge ignition
  J. Stephens, A. Fierro, J. Dickens, and A. Neuber, "Micrometer-resolution high speed imaging of pulsed microdischarge ignition," IEEE Trans. On Plasma Sci. 42, 2652 - 2653 (2014).
Abstract:  The application of a short, pulsed excitation is known to allow for higher power deposition into microdischarges without the onset of instabilities. Here, a MOSFET-based high voltage pulser is used to drive a 50-torr argon microdischarge with short pulsed currents of ~75 A, with <100-ns full-width at half-maximum, and a repetition rate of 1 MHz. With this excitation, an average power density of ~1e13 W/m3 is achieved, with a peak power density~3e14 W/m3. A high speed iCCD camera is used to observe ignition processes and confirm the absence of unstable operation. The images were taken using a 5-ns gate time with a spatial resolution of ~2.5 μm.

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+ Nanosecond, repetitively pulsed microdischarge vacuum ultraviolet source
  J. Stephens, A. Fierro, B. Walls, J. Dickens, A. Neuber, "Nanosecond, repetitively pulsed microdischarge vacuum ultraviolet source," Applied Physics Letters 104 (7), 074105, (2014).
Abstract:  A microdischarge is driven by short pulses (80 ns FWHM) with peak current levels up to 80 A, with a repetition frequency of 1 MHz (1 pulse/μs) allowing for ∼550 W input power. Experiments in pure argon (Ar2*, 127 nm) and argon-hydrogen (Lyman-α, 121.6 nm) were conducted. Using short pulses, the argon excimer emission was not observed. Alternatively, Ar-H2 operated at both higher power and efficiency (0.63%) whenever pulsed. Using Ar-H2, the experiments result in an average generated vacuum ultraviolet power just above 3.4 W with a peak power of 42.8 W, entirely at Lyman-α.

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+ Piezoelectric Ignition of Nanocomposite Energetic Materials
  E. Collins, M. Pantoya, AA. Neuber, M. Daniels, "Piezoelectric Ignition of Nanocomposite Energetic Materials," Journal of Propulsion and Power 30 (1), 15-18, (2014).
Abstract:  Piezoelectric initiators are a unique form of ignition for energetic material because the current and voltage are tied together by impact loading on the crystal. This study examines the ignition response of an energetic composite composed of aluminum and molybdenum trioxide nanopowders to the arc generated from a lead zirconate and lead titanate piezocrystal. The mechanical stimuli used to activate the piezocrystal varied to assess ignition voltage, power, and delay time of aluminum-molybdenum trioxide for a range of bulk powder densities. Results show a high dielectric strength leads to faster ignition times because of the higher voltage delivered to the energetic. Ignition delay is under 0.4 ms, which is faster than observed with thermal or shock ignition. Electric ignition of composite energetic materials is a strong function of interparticle connectivity, and thus the role of bulk density on electrostatic discharge ignition sensitivity is a focus of this study. Results show that the ignition delay times are dependent on the powder bulk density with an optimum bulk density of 50%. Packing fractions and electrical conductivity were analyzed and aid in explaining the resulting ignition behavior as a function of bulk density. Read More: http://arc.aiaa.org/doi/abs/10.2514/1.B35034

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+ Safe Operating Area and Long-Term Reliability of 9-kV Silicon Carbide PNPN Super Gate Turn-Off Thyristors
  K. Lawson et al., "Safe Operating Area and Long-Term Reliability of 9-kV Silicon Carbide PNPN Super Gate Turn-Off Thyristors," in IEEE Electron Device Letters, vol. 35, no. 8, pp. 862-864, Aug. 2014.
Abstract:  One of the major requirements for adoption of new silicon carbide (SiC) super gate turn-off thyristors (SGTOs) into high-energy applications is to verify the safe operating area and long-term reliability capabilities of these devices. In this letter, we have developed a unique high-energy testing system that can evaluate the performance limitations with respect to lifetime capabilities of the 9 kV, 1 cm2, SGTOs at ultrahigh pulsed current levels from 1 to 3.5 kA. The test system produces square current pulses with a user specified current amplitude and a 100-μs pulsewidth at a maximum repetition rate of 1 shot/s (>0.1% duty cycle). A lifetime safe operating area with respect to maximum pulsed current was then established that these 1 cm2, 9 kV, SiC SGTOs can perform reliably without significant degradation at pulsed current levels up to 2.0 kA. At current levels above 2.0 kA shifts in the on-state voltage are observed probably due to device over-heating at such high current levels and having not enough time to fully dissipate the heat between any two shots, which results in the device rapidly deteriorating due to increased on-state losses ultimately leading to premature failure.

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+ Semiempirical wide-range conductivity model with exploding wire verification
  J Stephens, J Dickens, and A Neuber, "Semiempirical wide-range conductivity model with exploding wire verification," Physical Review E 89 (5), 053102 (2014).
Abstract:  Based on well-established physical relationships, a semiempirical set of equations dictating the electrical conductivity of dense, strongly coupled, partially ionized copper is presented. With the empirical coefficients, the model is tuned to experimental conductivity data obtained from exploding wire experiments [A. W. DeSilva and J. D. Katsouros, Phys. Rev. E 57, 5945 (1998)]. The result is a wide-range conductivity model, with demonstrated accuracy from room temperature-density conditions to 0.01 g/cm3 and 30 kK. Using magnetohydrodynamic simulation the ability to utilize the conductivity model for predictive simulations is demonstrated. A complete electrical conductivity dataset for copper has been made available to the public.

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+ System for Time-Discretized VUV Spectroscopy of Spark Breakdown in Air
  D. Ryberg, A. Fierro, J. Dickens, and A. Neuber,"System for Time-Discretized VUV Spectroscopy of Spark Breakdown in Air," Rev. Sci. Inst. 85, 103109 (2014).
Abstract:  A system for time-discretized spectroscopic measurements of the vacuum ultraviolet (VUV) emission from spark discharges in the 60-160 nm range has been developed for the study of early plasma-forming phenomena. The system induces a spark discharge in an environment close to atmospheric conditions created using a high speed puff value, but is otherwise kept at high vacuum to allow for the propagation of VUV light. Using a vertical slit placed 1.5 mm from the discharge the emission from a small cross section of the discharge is allowed to pass into the selection chamber consisting of a spherical grating, with 1200 grooves/mm, and an exit slit set to 100 μm. Following the exit slit is a photomultiplier tube with a sodium salicylate scintillator that is used for the time discretized measurement of the VUV signal with a temporal resolution limit of 10 ns. Results from discharges studied in dry air, Nitrogen, SF6, and Argon indicate the emission of light with wavelengths shorter than 120 nm where the photon energy begins to approach the regime of direct photoionization.

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+ Temporally resolved electron density of a repetitive, nanosecond pulsed microdischarge
  J. Stephens, A. Fierro, J. Dickens, and A. Neuber, "Temporally resolved electron density of a repetitive, nanosecond pulsed microdischarge" Journal of Physics D: Applied Physics 47, 465205 (2014).
Abstract:  Using high speed spectroscopic diagnostics, temporally resolved optical emission spectroscopy is performed on a nanosecond, repetitively pulsed microdischarge. The microdischarge operates in an argon-hydrogen gas mixture (99%/1%) to provide a Lyman-α vacuum ultraviolet emission. Based on the Stark broadening of the 486.1 nm, Balmer-β hydrogen transition, the temporally resolved electron density was determined. Experimental electron density data are compared with the results of a 0D rate equation model. Peak electron density is estimated to be 5.6e15 1 cm-3, corresponding to a ~0.25% degree of ionization. Using the approximate experimental ionization rate, the electron temperature is estimated to be ~3.5 eV.

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Publication Year:  2013
+ A compact 45 kV curve tracer with picoampere current measurement capability
  W.W. Sullivan, D. Mauch, A. Bullick, C. Hettler, A. Neuber, J. Dickens, "A compact 45 kV curve tracer with picoampere current measurement capability," Rev. Sci. Inst. 84, 034702 (2013).
Abstract:  This paper discusses a compact high voltage curve tracer for high voltage semiconductor device characterization. The system sources up to 3 mA at up to 45 kV in dc conditions. It measures from 328 V to 60 kV with 15 V resolution and from 9.4 pA to 4 mA with 100 fA minimum resolution. Control software for the system is written in Microsoft Visual C# and features real-time measurement control and IV plotting, arc-protection and detection, an electrically isolated universal serial bus interface, and easy data exporting capabilities. The system has survived numerous catastrophic high voltage device-under-test arcing failures with no loss of measurement capability or system damage. Overall sweep times are typically under 2 min, and the curve tracer system was used to characterize the blocking performance of high voltage ceramic capacitors, high voltage silicon carbide photoconductive semiconductor switches, and high voltage coaxial cable.

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+ All solid-state high power microwave source with high repetition frequency
  J.-W. Bragg, W. Sullivan, D. Mauch, A. Neuber, J. Dickens, "All solid-state high power microwave source with high repetition frequency," Review of Scientific Instruments, 84(5), 054703 - 054703-7 (2013)
Abstract:  An all solid-state, megawatt-class high power microwave system featuring a silicon carbide (SiC) photoconductive semiconductor switch (PCSS) and a ferrimagnetic-based, coaxial nonlinear transmission line (NLTL) is presented. A 1.62 cm2, 50 kV 4H-SiC PCSS is hard-switched to produce electrical pulses with 7 ns full width-half max (FWHM) pulse widths at 2 ns risetimes in single shot and burst-mode operation. The PCSS resistance drops to sub-ohm when illuminated with approximately 3 mJ of laser energy at 355 nm (tripled Nd:YAG) in a single pulse. Utilizing a fiber optic based optical delivery system, a laser pulse train of four 7 ns (FWHM) signals was generated at 65 MHz repetition frequency. The resulting electrical pulse train from the PCSS closely follows the optical input and is utilized to feed the NLTL generating microwave pulses with a base microwave-frequency of about 2.1 GHz at 65 MHz pulse repetition frequency (prf). Under typical experimental conditions, the NLTL produces sharpened output risetimes of 120 ps and microwave oscillations at 2-4 GHz that are generated due to damped gyromagnetic precession of the ferrimagnetic material's axially pre-biased magnetic moments. The complete system is discussed in detail with its output matched into 50 Ω, and results covering MHz-prf in burst-mode operation as well as frequency agility in single shot operation are discussed.

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+ Ferrimagnetic Nonlinear Transmission Lines as High-Power Microwave Sources
  J.-W. Bragg, J. Dickens, and A. Neuber, “"Ferromagnetic Nonlinear Transmission Lines as High Power Microwave Source" IEEE Trans. on Plasma Sci. 41, 232-237, 2013.
Abstract:  Ferrimagnetic nonlinear transmission lines (NLTLs) have the potential to fill a high-power microwave niche where compact cost-effective sources are lacking. NLTLs utilize nonlinear ferrimagnetic properties and magnetization dynamics to provide ultrafast pulse rise times (100 ps or less) and microwave signals with peak power ranging from kilowatts to hundreds of megawatts. The frequency of operation has been shown to range from 900 MHz up to 5 GHz depending on geometry and external magnetic fields. NLTLs, theoretically, can be pulsed to tens of kilohertz with little to no variance in microwave signal between shots. This paper covers recent advances in ferrimagnetic-based NLTLs, specifically effects of applied and bias magnetic fields on peak power and frequency, as well as temperature dependence.

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+ Focused cathode design to reduce anode heating during vircator operation
  C. F. Lynn, J. C. Dickens, and A. A. Neuber, "Focused cathode design to reduce anode heating during vircator operation," Phys. Plasmas 20, 103113 (2013).
Abstract:  Virtual cathode oscillators, or vircators, are a type of high power microwave device which operates based on the instability of a virtual cathode, or cloud of electrons, which forms when electron current injected into the drift tube exceeds the space charge limited current within the drift tube. Anode heating by the electron beam during vircator operation ultimately limits achievable pulse lengths, repetition rates, and the duration of burst mode operation. This article discusses a novel cathode design that focuses electrons through holes in the anode, thus significantly reducing anode heating by the electrons emitted from the cathode during the first transit through the A-K gap. Reflexing electrons continue to deposit energy on the anode; however, the discussed minimization of anode heating by main beam electrons has the potential to enable higher repetition rates as well as efficiency and longer diode lifetime. A simulation study of this type of cathode design illustrates possible advantages.

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+ Material selection considerations for coaxial, ferrimagnetic-based nonlinear transmission lines
  J.-W. B. Bragg, J. C. Dickens, and A. A. Neuber, "Material selection considerations for coaxial, ferrimagnetic-based nonlinear transmission lines," J. Appl. Phys. 113, 064904, (2013).
Abstract:  The growing need for solid-state high power microwave sources has renewed interest in nonlinear transmission lines (NLTLs). This article focuses specifically on ferrimagnetic-based NLTLs in a coaxial geometry. Achieved peak powers exceed 30 MW at 30 kV incident voltage with rf power reaching 4.8 MW peak and pulse lengths ranging from 1-5 ns. The presented NLTL operates in S-band with the capability to tune the center frequency of oscillation over the entire 2-4 GHz band and bandwidths of approximately 30%, placing the NLTL into the ultra-wideband-mesoband category of microwave sources. Several nonlinear materials were tested and the relationship between NLTL performance and material parameters is discussed. In particular, the importance of the material's ferromagnetic resonance linewidth and its relationship to microwave generation is highlighted. For a specific nonlinear material, it is shown that an optimum relation between incident pulse magnitude and static bias magnitude exists. By varying the nonlinear material's bias magnetic field, active delay control was demonstrated.

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+ Plasma relaxation mechanics of pulsed high power microwave surface flashover
  S. Beeson, J. Dickens, and A. Neuber, "Plasma relaxation mechanics of pulsed high power microwave surface flashover," Physics of Plasmas 20(9), 093509 - 093509-9 (2013).
Abstract:  Microwave transmission and reflection characteristics of pulsed radio frequency field generated plasmas are elucidated for air, N2, and He environments under pressure conditions ranging from 10 to 600 torr. The pulsed, low temperature plasma is generated along the atmospheric side of the dielectric boundary between the source (under vacuum) and the radiating environment with a thickness on the order of 5 mm and a cross sectional area just smaller than that of the waveguide. Utilizing custom multi-standard waveguide couplers and a continuous low power probing source, the scattering parameters were measured before, during, and after the high power microwave pulse with emphasis on the latter. From these scattering parameters, temporal electron density estimations (specifically the longitudinal integral of the density) were calculated using a 1D plane wave-excited model for analysis of the relaxation processes associated. These relaxation characteristics ultimately determine the maximum repetition rate for many pulsed electric field applications and thus are applicable to a much larger scope in the plasma community than just those related to high power microwaves. This manuscript discusses the diagnostic setup for acquiring the power measurements along with a detailed description of the kinematic and chemical behavior of the plasma as it decays down to its undisturbed state under various gas type and pressure conditions.

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+ Simultaneous measurement of nitrogen and hydrogen dissociation from vacuum ultraviolet self-absorption spectroscopy in a developing low temperature plasma at atmospheric pressure
  G. Laity, A. Fierro, J. Dickens, A. Neuber, and K. Frank, "Simultaneous measurement of nitrogen and hydrogen dissociation from vacuum ultraviolet self-absorption spectroscopy in a developing low temperature plasma at atmospheric pressure," Appl. Phys. Letters, 102, 184104, (2013).
Abstract:  We demonstrate a method for determining the dissociation density of N and H atoms present in a developing low temperature plasma, based on the emission and self-absorption of vacuum ultraviolet radiation produced from the plasma. Spark plasmas are produced via pulsed discharge in N2/H2 mixtures at atmospheric pressure, where information on the dissociated densities of the constituent gas molecules is desired without employing invasive diagnostic techniques. By analyzing the self-absorption line profile of 121.5 nm Lyman-α H radiation emitted within the first ∼1.0 mm of plasma near the anode tip, a peak dissociated H atom concentration of 5.6e17 1/cm3 was observed ∼100 ns into spark formation, with an estimated electron density of 2.65 e18 1/cm3 determined from Stark broadening. Similarly, simultaneous line fitting of the N 120.0/124.3 nm emission profiles revealed a peak dissociated N atom concentration of 3.8e17 1/cm during the same discharge period.

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Publication Year:  2012
+ A finite-difference time-domain simulation of high power microwave generated plasma at atmospheric pressures
  P. J. Ford, S. R. Beeson, H. G. Krompholz, and Andreas A. Neuber, "A finite-difference time-domain simulation of high power microwave generated plasma at atmospheric pressures," Phys. Plasmas 19, 073503 (2012), DOI:10.1063/1.4736863
Abstract:  A finite-difference algorithm was developed to calculate several RF breakdown parameters, for example, the formative delay time that is observed between the initial application of a RF field to a dielectric surface and the formation of field-induced plasma interrupting the RF power flow. The analysis is focused on the surface being exposed to a background gas pressure above 50 Torr. The finite-difference algorithm provides numerical solutions to partial differential equations with high resolution in the time domain, making it suitable for simulating the time evolving interaction of microwaves with plasma; in lieu of direct particle tracking, a macroscopic electron density is used to model growth and transport. This approach is presented as an alternative to particle-in-cell methods due to its low complexity and runtime leading to more efficient analysis for a simulation of a microsecond scale pulse. The effect and development of the plasma is modeled in the simulation using scaling laws for ionization rates, momentum transfer collision rates, and diffusion coefficients, as a function of electric field, gas type and pressure. The incorporation of plasma material into the simulation involves using the Z-transform to derive a time-domain algorithm from the complex frequency-dependent permittivity of plasma. Therefore, the effect of the developing plasma on the instantaneous microwave field is calculated. Simulation results are compared with power measurements using an apparatus designed to facilitate surface flashover across a polycarbonate boundary in a controlled N2, air, or argon environment at pressures exceeding 50 Torr.

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+ An Explosively Driven High Power Microwave Pulsed Power System
  M. Elsayed, A. Neuber, J. Dickens, J. Walter, M. Kristiansen, and L. Altgilbers, "An Explosively Driven High Power Microwave Pulsed Power System," Rev. Sci. Instrum. 83, 024705 (2012).
Abstract:  The increased popularity of high power microwave systems and the various sources to drive them is the motivation behind the work to be presented. A stand-alone, self-contained explosively driven high power microwave pulsed power system has been designed, built, and tested at Texas Tech University's Center for Pulsed Power and Power Electronics. The system integrates four different sub-units that are composed of a battery driven prime power source utilizing capacitive energy storage, a dual stage helical flux compression generator as the main energy amplification device, an integrated power conditioning system with inductive energy storage including a fast opening electro-explosive switch, and a triode reflex geometry virtual cathode oscillator as the microwave radiating source. This system has displayed a measured electrical source power level of over 5 GW and peak radiated microwaves of about 200 MW. It is contained within a 15 cm diameter housing and measures 2 m in length, giving a housing volume of slightly less than 39 l. The system and its sub-components have been extensively studied, both as integrated and individual units, to further expand on components behavior and operation physics. This report will serve as a detailed design overview of each of the four subcomponents and provide detailed analysis of the overall system performance and benchmarks.

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+ Design and Testing of Multi-Standard Waveguide Couplers
  S. Beeson and A. Neuber, "Design and Testing of Multi-Standard Waveguide Couplers," Rev. Sci. Instrum. 83, 034702 (2012).
Abstract:  Most applications that use waveguides are designed for a single frequency or single band of frequency, and thus the waveguide dimensions are chosen for single mode operation. In special cases where multiple frequencies across multiple bands are needed (i.e., probing the temporal response of decaying plasma using a cw source that is generated by a pulsed source), special techniques must be used in order to implement both sources into a single waveguide structure. This paper presents two types of couplers designed to implement x-band frequencies into an s-band system with a large coupling coefficient (< −10 dB) and small reflection coefficient (> −10 dB) at the design frequency of 11 GHz. Along with a discussion on the design procedure, a detailed description on the parameter optimization and initial values estimation is presented. The custom waveguide structures were tested utilizing an Agilent E8364B PNA network analyzer, and showed reasonable agreement with the simulated performance over the frequency range of interest.

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+ Electric field enhanced conductivity in strongly coupled dense metal plasma
  J. Stephens and A. Neuber, "Electric field enhanced conductivity in strongly coupled dense metal plasma," Phys. Plasmas 19, 060702 (2012).
Abstract:  Experimentation with dense metal plasma has shown that non-negligible increases in plasma conductivity are induced when a relatively low electric field (∼6 kV/cm) is applied. Existing conductivity models assume that atoms, electrons, and ions all exist in thermal equilibrium. This assumption is invalidated by the application of an appreciable electric field, where electrons are accelerated to energies comparable to the ionization potential of the surrounding atoms. Experimental data obtained from electrically exploded silver wire is compared with a finite difference hydrodynamic model that makes use of the SESAME equation-of-state database. Free electron generation through both thermal and electric field excitations, and their effect on plasma conductivity are applied and discussed.

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+ Experimental and Theoretical Evaluation of Surface Coated Exploding Wires
  J. Stephens, A. Neuber, and M. Kristiansen, "Experimental and Theoretical Evaluation of Surface Coated Exploding Wires," Phys. Plasmas 19, 032702 (2012).
Abstract:  This paper discusses the effect of surface coatings on exploding wire behavior. Three different surface coatings of different thicknesses and materials have been studied, each with a 99.99% pure silver conducting core. Experimentally, the wires are subjected to peak current densities in excess of 107 A/cm2 on a microsecond time scale. High Speed intensified Charge-Coupled Device (iCCD) images. A theoretical one-dimensional finite difference model has been developed to predict wire behavior and determine the mechanism(s) responsible for the deviations in behavior induced by the presence of a surface coating.

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+ Investigation into the Temperature Dependence of Ferrimagnetic Nonlinear Transmission Lines
  J.-W. Bragg, J. Dickens, and A. Neuber, "Investigation into the Temperature Dependence of Ferrimagnetic Nonlinear Transmission Lines," IEEE Trans. Plasma Sci. 99, pp. 1-5 (2012).
Abstract:  In pulsed power systems, coaxial based nonlinear transmission lines (NLTLs) loaded with ferrimagnetic materials act as pulse sharpeners or high power microwave sources. Microwave generation comes by way of nonlinearities present in the ferrimagnetic material as well as excitation of damped gyromagnetic precession at large incident power levels. Ferrimagnetic properties highly depend on operating temperature; therefore, there exists a need to understand operational performance of ferrite loaded NLTLs under different temperature environments. Ferrite samples are chilled or heated to temperatures between $-20 ^{circ}hbox{C}$ to 150 $^{circ}hbox{C}$, providing a wide range of possible operating temperatures. The Curie temperature of the tested samples is approximately 120 $^{circ}hbox{C}$; therefore, this study allows observation of precession performance in possible operating temperatures as well as a brief look at the consequences of exceeding the Curie temperature. The design, testing, and results for an NLTL measuring 0.3 m in length with ferrite inner and outer diameters of 3 mm and 6 mm, respectively, are detailed. Results reveal precessional performance, both peak power and frequency of oscillations, versus temperature.

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+ The Impact of Wire Environment on Electro-Explosive Fuse Performance
  J. Stephens, W. Mischke, A. Neuber, "The Impact of Wire Environment on Electro-Explosive Fuse Performance", to be published in IEEE Trans. Plasma Sci. (2012).
Abstract:  The environment surrounding an exploding wire is known be a controlling factor in electro-explosive fuse performance. Recent experiments have shown that the application of an insulating surface coating to the fuse wire can significantly increase the rate of impedance transition and impedance magnitude of the exploding wire. This paper discusses the performance of surface coated fuses tested in commonly used solid and gaseous media. For comparison, these experiments are compared to bare wire fuse experiments in identical environments. Previously developed exploding wire models are utilized to aid in the interpretation of the experimental fuse behavior. Differential wire voltage, voltage pulse length, and degree of post vaporization conduction (i.e., restrike) are discussed for each experiment.

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Publication Year:  2011
+ Imaging of Pressure-Dependent High-Power Microwave Surface Flashover
  S. Beeson, P. Ford, J. Foster, H. Krompholz, and A. Neuber, "Imaging of Pressure-Dependent High-Power Microwave Surface Flashover," IEEE Transactions on Plasma Science 39, 2600-2601, (2011).
Abstract:  Open-shutter and intensified charge-coupled device images of high-power microwave breakdown were taken in an effort to characterize the pressure dependence of plasma development. These images were taken with a Nikon D200 and Andor iStar DH734-25U-03, respectively. With the pressures increasing from 200 mtorr to 155 torr, the plasma changes from a diffuse discharge encompassing a large volume to a multichannel structure following the electric field lines.

[PDF]

+ Investigation of the Delay Time Distribution of High Power Microwave Surface Flashover
  J. Foster, H. Krompholz, A. Neuber, "Investigation of the Delay Time Distribution of High Power Microwave Surface Flashover," Physics of Plasmas 18, 013502 (2011).
Abstract:  Characterizing and modeling the statistics associated with the initiation of gas breakdown has proven to be difficult due to a variety of rather unexplored phenomena involved. Experimental conditions for high power microwave window breakdown for pressures on the order of 100 to several 100 torr are complex: there are little to no naturally occurring free electrons in the breakdown region. The initial electron generation rate, from an external source, for example, is time dependent and so is the charge carrier amplification in the increasing radio frequency (RF) field amplitude with a rise time of 50 ns, which can be on the same order as the breakdown delay time. The probability of reaching a critical electron density within a given time period is composed of the statistical waiting time for the appearance of initiating electrons in the high-field region and the build-up of an avalanche with an inherent statistical distribution of the electron number. High power microwave breakdown and its delay time is of critical importance, since it limits the transmission through necessary windows, especially for high power, high altitude, low pressure applications. The delay time distribution of pulsed high power microwave surface flashover has been examined for nitrogen and argon as test gases for pressures ranging from 60 to 400 torr, with and without external UV illumination. A model has been developed for predicting the discharge delay time for these conditions. The results provide indications that field induced electron generation, other than standard field emission, plays a dominant role, which might be valid for other gas discharge types as well.

[PDF]

+ Modeling statistical variations in high power microwave breakdown
  J. Krile and A. Neuber, "Modeling statistical variations in high power microwave breakdown," Appl. Phys. Lett. 98, 211502, (2011).
Abstract:  Flashover of high power microwave (HPM) vacuum isolation windows presents a serious design limitation of megawatt class HPM systems. The delay time from HPM radiation incident on the window to flashover development on the atmospheric side is critical. Previously developed modeling efforts have yielded reasonable correlation with experimentally observed average delay times while failing to capture any statistical variations. Simply preseeding the volume with an initial electron density is identified as inadequate to describe the source of initiatory electrons. The process of field assisted electron detachment is examined and shown to be a probable candidate for the initiatory electron generation.

[PDF]

+ Phenomenology of Streamer Propagation during Pulsed Dielectric Surface Flashover
  G. Laity, A. Neuber, A. Fierro, L. Hatfield, "Phenomenology of Streamer Propagation during Pulsed Dielectric Surface Flashover," IEEE Transactions on Dielectrics and Electrical Insulation 18, pp. 946-953, (2011).
Abstract:  There is a growing demand for understanding the physics of surface flashover, as it relates to the breakdown of electric fields on high power systems in the aerospace community. Specifically, the quantitative role of vacuum ultraviolet (VUV) radiation which is self-produced during the initial nanoseconds of surface flashover is virtually unknown. An experiment was constructed which allows detailed electrical and optical measurements of VUV emission during the timescales in which streamers are propagating before the transition into spark discharge. Repeated surface flashover events are generated using a solid-state high voltage pulser, with breakdown recorded in a number of gases at atmospheric pressure. Streamers are photographed using fast optical imaging with 3 ns resolution. Fast voltage and current diagnostics revealed a number of distinct stages of streamer development ranging from the onset of cathode directed streamers to the sharp current rise during final voltage collapse. The emission of VUV radiation is discussed in context to the observed streamer and electrical characteristics.

[PDF]

+ Rapid Formation of Dielectric Surface Flashover due to Pulsed High Power Microwave Excitation
  J. Foster, S. Beeson, H. Krompholz, A. Neuber, "Rapid Formation of Dielectric Surface Flashover due to Pulsed High Power Microwave Excitation," IEEE Transactions on Dielectrics and Electrical Insulation 18, pp. 964-970 (2011).
Abstract:  High power microwave (HPM) dielectric surface flashover can be rapidly induced by providing breakdown initiating electrons in the high field region. An experimental setup utilizing a 2.85 GHz HPM source to produce a 4.5 MW, 3 μs pulse is used for studying HPM surface flashover in various atmospheric conditions. If flashover is to occur rapidly in an HPM system, it is desirable to provide a readily available source of electrons while keeping insertion loss at a minimum. The experimental results presented in this paper utilize a continuous UV source (up to 0.3 mW/cm2) to provide photo-emitted seed electrons from the dielectric surface. Similarly, electrons were provided through the process of field emission by using metallic points deposited on the surface. Initial experiments utilizing 0.2 mm2 aluminum points with a spatial density of 25/cm2 have increased the apparent effective electric field by a factor of ~1.5 while keeping the insertion loss low (<0.01 dB). The field enhancements have sharply reduced the delay time for surface flashover. For an environment consisting of air at 2.07x104 Pa (155 Torr), for instance, the delay time is reduced from 455 ns to 101 ns. Two radioactive sources were also used in an attempt to provide seed electrons in the high field regions. Presented in this paper is a comparison of various field-enhancing geometries and how they relate to flashover development along with an analysis of time resolved imaging and an explanation of experimental results with radioactive materials.

[PDF]

+ Spatially Resolved Vacuum UV Spectral Imaging of Pulsed Atmospheric Flashover
  G. Laity, A. Fierro, L. Hatfield, J. Dickens, and A. Neuber, "Spatially Resolved Vacuum UV Spectral Imaging of Pulsed Atmospheric Flashover," to be published in IEEE Transactions on Plasma Science, (2011).
Abstract:  Not Available

[PDF]

+ Statistical analysis of high power microwave breakdown surface flashover delay times in nitrogen with metallic field enhancements
  J. Foster, H. Krompholz, and A. Neuber, "Statistical analysis of high power microwave breakdown surface flashover delay times in nitrogen with metallic field enhancements," Phys. Plasmas 18, 113505, (2011).
Abstract:  The physical mechanisms that contribute to atmospheric breakdown induced by high power microwaves (HPMs) are of particular interest for the further development of high power microwave systems and related technologies. For a system in which HPM is produced in a vacuum environment for the purpose of radiating into atmosphere, it is necessary to separate the atmospheric environment from the vacuum environment with a dielectric interface. Breakdown across this interface on the atmospheric side and plasma development to densities prohibiting further microwave propagation are of special interest. In this paper, the delay time between microwave application and plasma emergence is investigated. Various external parameters, such as UV illumination or the presence of small metallic points on the surface, provide sources for electron field emission and influence the delay time which yields crucial information on the breakdown mechanisms involved. Due to the inherent statistical appearance of initial electrons and the statistics of the charge carrier amplification mechanisms, the flashover delay times deviate by as much as ±50% from the average, for the investigated case of discharges in N2 at pressures of 60–140 Torr and a microwave frequency of 2.85 GHz with 3 μs pulse duration, 50 ns pulse risetime, and MW/cm2 power densities. The statistical model described in this paper demonstrates how delay times for HPM surface flashover events can be effectively predicted for various conditions given sufficient knowledge about ionization rate coefficients as well as the production rate for breakdown initiating electrons.

[PDF]

Publication Year:  2010
+ Capacitor Evaluation for Compact Pulsed Power
  E. J. Matthews, M. Kristiansen, A. A. Neuber, "Capacitor Evaluation for Compact Pulsed Power", IEEE Transaction on Plasma Science 38, 500-508 (2010)
Abstract:  An evaluation of the energy density and efficiency of high-voltage capacitors, from various manufacturers, at voltages above their rated level is presented. Characteristics such as decreasing capacitance, decreasing efficiency, and increasing energy density are described. Data are taken from eight capacitors; six of which are composed of varying nonlinear ceramic materials as a dielectric, and the remaining two are wound capacitors, which were chosen to exhibit their linear characteristics. Rapid (1-100 ms) charging and discharging, similar to that of a generator operation at a repetition rate of more than 10 Hz with an ~100-ns pulse, were the conditions simulated in this particular test setup.

[PDF]

+ Characterization of a 50 J Linear Transformer Driver
  David Matia, Hermann Krompholz, Travis Vollmer, Andreas Neuber, Michael Giesselmann, Magne Kristiansen, "Characterization of a 50 J Linear Transformer Driver", Proceedings of the 2010 IEEE International Power Modulator and High Voltage Conference, May 23-27, 2010, Atlanta, GA.
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.

[PDF]

+ Development of a 40-stage distributed energy railgun
  Karhi, R.; Giesselmann, M.; Wetz, D.; Diehl, J.; "Development of a 40-stage distributed energy railgun "; Pulsed Power Conference, 2009. PPC '09. IEEE Digital Object Identifier: 10.1109/PPC.2009.5386257 Publication Year: 2009 , Page(s): 747 - 752
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. Outcom- es of these initial experimental results will aid the development of the 40-stage system.

[PDF]

+ Modeling and Simulation of Simple Flux-Trapping FCGs Utilizing PSpice Software
  Young, A.; Neuber, A.; Kristiansen, M.; "Modeling and Simulation of Simple Flux-Trapping FCGs Utilizing PSpice Software"; Plasma Science, IEEE Transactions on Volume: 38 , Issue: 8 , Part: 1; Publication Year: 2010 , Page(s): 1794 - 1802
Abstract:  A novel modeling and simulation method for flux-trapping flux-compression generators (FT-FCGs) is presented, which utilizes PSpice circuit-simulation software to solve complex differential equations derived from circuit analysis. The primary motivation for the model development is the desire for a technique to rapidly design and prototype FT-FCGs for use as drivers in high-power microwave sources. The derivation of FT-FCG equations will be given, both in the ideal (lossless) and nonideal cases. For the nonideal case, three flux conservation coefficients are added to the equations to account for intrinsic flux loss in the circuit. Time-varying inductance curves are calculated using zero-dimensional models found in literature and adapted to fit this model. A simple FT-FCG design is used as an example to show the steps taken to complete a simulation. The same design was also fabricated and tested for comparison with predicted results from the model. A comparison of the waveforms acquired through simulation and experiment was found to result in good agreement for a given set of values for the flux conservation coefficients. A discussion of the derived equations, both lossless and nonideal, is given, as well as a discussion on the investigation of the impact of the three flux constants on the circuit. Analysis is offered on the results of this investigation, and conclusions are given on the effectiveness of this model to predict FT-FCG behavior.

[PDF]

+ Pulsed magnetic field excitation sensitivity of match-type electric blasting caps
  J. Parson, J. Dickens, J. Walter, A. Neuber, "Pulsed magnetic field excitation sensitivity of match-type electric blasting caps," Review of Scientific Instruments 81, pp. 105115-105115-7 (2010).
Abstract:  This paper presents a study on energy deposition and electromagnetic compatibility of match-type electroexplosive devices (EEDs), which recently have found more usage in pulsed power environments with high electromagnetic interference (EMI) background. The sensitivity of these devices makes them dangerous to intended and unintended radiation produced by devices commonly used in pulsed power environments. Match-type EEDs have been found to be susceptible to such low levels of energy (7-8 mJ) that safe operation of these EEDs is vital when in use near devices that produce high levels of pulsed EMI. The scope of this paper is to provide an investigation that incorporates results of similar studies to provide detonation characteristics of these EEDs. The three topics included in this study are sensitivity testing, modeling of the thermodynamic heat propagation, and electromagnetic compatibility from pulsed electromagnetic radiation. The thermodynamic joule heating of the primary explosive has been modeled by a solution to the 1D heat equation. A simple pulsed generator, Marx generator with an inductive load, was used for the electromagnetic compatibility assessment of the coupled field between the pulse generator and shorted EED. The results of the electromagnetic compatibility assessment relate the resistive, inductive, and capacitive components of the pulse generator to the area of the shorted EED.

[PDF]

+ Simulation of Compact Explosively-Driven Ferroelectric Generators
  D. Bolyard, T. Krile, A. Neuber, M. Kristiansen, "Simulation of Compact Explosively-Driven Ferroelectric Generators", IEEE Trans. On Plasma Sci. 38, 1008 - 1014 (2010)
Abstract:  Pressure simulations have been performed for several experimental explosively driven ferroelectric generators, with 2.54-cm-diameter PZT EC-64 discs as the ferroelectric material, using the hydrodynamic code system CTH, developed by Sandia National Laboratories. An empirical relationship was found between the results of the pressure simulations and the output voltages of the experimental generators, and an algorithm was generated to convert the simulated pressure into open-circuit voltage. This empirical algorithm has been applied to simulations of different experimental ferroelectric generators, and the results show a good correlation when compared to the corresponding experimental open-circuit output voltages. The experimentally achieved output voltages normalized for a thickness range from 14 to 34 kV/cm

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+ System for Time Resolved Spectral Studies of Pulsed Atmospheric Discharges in the Visible to VUV Range
  G. Laity, A. Neuber, G. Rogers, K. Frank, "System for Time Resolved Spectral Studies of Pulsed Atmospheric Discharges in the Visible to VUV Range", accepted for publication to Review of Scientific Instruments, 2010.
Abstract:  Vacuum ultraviolet (VUV) emission is believed to play a major role in the development of plasma streamers in pulsed atmospheric discharges, but detection of VUV light is difficult in pulsed experiments at atmospheric pressures. Since VUV light is absorbed in most standard optical materials as well, careful attention must be given to the selection of the lens and mirror optics used in these studies. Of highest interest is the VUV emission during the initial stage of pulsed atmospheric discharges, which has a typical duration in the nanosecond regime. An experiment was designed to study this fast initial stage of VUV emission coupled with fast optical imaging of streamer propagation, both with temporal resolution on the order of nanoseconds. A repetitive solid-state high voltage pulser was constructed which produces triggered flashover discharges with low jitter and consistent pulse amplitude. VUV emission is captured utilizing both photomultiplier and intensified charge-coupled device detectors during the fast stage of streamer propagation. These results are discussed in context with the streamer formation photographed in the visible wavelength regime with 3 ns exposure time.

[PDF]

+ VUV Emission and Streamer Formation in Pulsed Dielectric Surface Flashover at Atmospheric Pressure
  G. Rogers, A. Neuber, G. Laity, K. Frank, J. Dickens, "VUV Emission and Streamer Formation in Pulsed Dielectric Surface Flashover at Atmospheric Pressure", accepted for publication in IEEE Trans. On Plasma Sci. (2010).
Abstract:  There is a growing interest in the physics of surface flashover between the interface of atmosphere and vacuum in some high-power systems. More specifically, the quantitative role of vacuum ultraviolet (VUV) radiation for the photoionization leading to a streamer development during the initial stages of a breakdown is unknown. This paper describes an experimental setup used to measure the VUV radiation emitted from atmospheric flashover as well as time-resolved imaging of the flashover event. A pulser providing the voltage to the gap was designed with special considerations in mind, including long lifetime, low noise, and high reproducibility. This enabled the study of the flashover in various background gases with an emphasis on spectroscopic measurements. The calculated spectra are compared with the measured spectra, and it is found that atomic oxygen and nitrogen are responsible for most of the VUV production in an air breakdown at atmospheric pressure in the wavelength range of 115–180 nm. Time-resolved spectroscopy reveals that the VUV radiation is emitted during the initial stages while the streamers are developing.

[PDF]

Publication Year:  2009
+ Optimization of an FCG Based High Power Microwave System using Nonexplosive Pulsed Power
  C. Davis, A. Neuber, A. Young, J. Walter, J. Dickens, M. Kristiansen, "Optimization of an FCG Based High Power Microwave System using Nonexplosive Pulsed Power," IEEE Trans. On Plasma Science, 27, 2321- 2327 (Sept. 2009)
Abstract:  This paper presents a nonexplosive pulsed-power system that replicates the output current waveform of a flux compression generator (FCG). The primary purpose of this system is to efficiently test the power conditioning components of an explosively driven HPM system, while drastically reducing the time between tests which are inherent with explosive experiments. The power conditioning system (PCS) of the HPM system includes an energy-storage inductor, an electroexplosive opening switch (fuse), and a peaking gap and serves to match the FCG output characteristics with the HPM diode load requirements. A secondary purpose of the nonexplosive test bed is to provide data points which could be directly compared with those from explosively driven experiments. For this reason, a reflex-triode virtual cathode oscillator (vircator) was connected to the output of the nonexplosive system, and the results of which were compared with similar testing done with an FCG and a compact Marx generator. Since the behavior of the fuse is known to play a critical role in the performance of the PCS, a study was performed on the effect of different fuse designs on the overall performance of the PCS. Specifically, the quality of the electrical connection between the fuse wire array and the rest of the system was tested. Fuse design experiments were conducted with the nonexplosive test bed firing into a water resistor dummy load, which showed a 13% increase in peak load voltage and more than an 11% increase in energy transfer for fuses with improved wire-electrode connection strength. Some basic rules about fuse design, as well as conclusions on the performance of the PCS when driving an HPM load, are given.

[PDF]

+ Plasma Structures Observed in Gas Breakdown Using a 1.5-MW, 110-GHz Pulsed Gyrotron
  Y. Hidaka, E. M. Choi, I. Mastovsky, M. A. Shapiro, J. R. Sirigiri, and R. J. Temkin, G. F. Edmiston, A. A. Neuber, and Y. Oda, "Plasma Structures Observed in Gas Breakdown Using a 1.5-MW, 110-GHz Pulsed Gyrotron", Phys. Plasmas 16, 055702 (2009).
Abstract:  Not Available
+ Recent Advances in Explosive Pulsed Power
  L.L. Altgilbers, A.H. Stults, M. Kristiansen, A. Neuber, J. Dickens, A. Young, T. Holt, M. Elsayed, R. Curry, K. O’Connor, J. Baird, S. Shkuratov, B. Freeman, D. Hemmert, F. Rose, Z. Shotts, Z. Roberts, W. Hackenberger, E. Alberta, M. Rader, A. Dougherty, "Recent Advances in Explosive Pulsed Power,", Journal of Directed Energy, 3, 1-43 (2009)
Abstract:  Not Available
+ Short Pulse High Power Microwave Surface Flashover at 3 GHz
  J. Krile, L McQuage, G. Edmiston, J. Walter, A. Neuber, "Short Pulse High Power Microwave Surface Flashover at 3 GHz", IEEE Trans. On Plasma Sci. 37, pp. 2139-2145 (2009)
Abstract:  High power microwave (HPM) induced surface flashover is investigated in order to gain a better understanding of this phenomenon and reduce the limitations it imposes on transmitted power levels. This work builds on previous testing using a magnetron producing 5 MW for 4 ¿s at 2.85 GHz. Both the previous and current experimental setups are designed to produce a flashover on the high pressure side of a transmission window without the influence of a triple point. Limitations of the previous experiment included a maximum power of 5 MW and a pulse rise time of 50 ns. The current HPM source is an experimental virtual cathode oscillator (vircator), the output of which has been extensively characterized. The vircator is capable of producing 50 MW peak for 100 ns with an adjustable frequency from 3 to 5 GHz and a rise time of < 4 ns. The dominant modes of the vircator and magnetron are the circular TE11 and rectangular TE10 modes respectively, with the major electric field component in both setups normal to the direction of propagation, yielding comparable field geometries at the transmission window. The experimental setup permits the study of factors including gas pressure, composition, temperature, and air speed. Diagnostic equipment allows the analysis of power levels and flashover luminosity with sub-nanosecond resolution.

[PDF]

+ Variation of the statistical and formative time lags of high power microwave surface flashover utilizing a superimposed DC electric field
  J. Foster, M. Thomas, A. A. Neuber, "Variation of the statistical and formative time lags of high power microwave surface flashover utilizing a superimposed DC electric field," J. Appl. Phys. 106, pp. 063310-063310-4 (2009).
Abstract:  In an effort to investigate the physics involved in the initiation of high power microwave surface flashover, a strong direct current (dc) electric field was introduced to the flashover region. The primary objective of this study is to demonstrate that an external electric field can have a significant impact on the delay time for surface flashover. It has been observed experimentally that the statistical and formative delay times for surface flashover can be varied depending on the polarity of the applied dc field. This external electric field may sweep possible breakdown initiating electrons away from the flashover region prior to the application of the high power microwave pulse. A distinct increase in the average statistical delay was observed primarily with a superimposed dc field in a positive polarity geometry as well as a decrease in the formative delay for either polarity in 167 mbar of nitrogen.

[PDF]

Publication Year:  2008
+ Breakdown Delay Times for Subnanosecond Gas Discharges at Pressures Below One Atmosphere
  J.E. Chaparro, W. Justis, H.G. Krompholz, L.L. Hatfield, A. A. Neuber, Breakdown Delay Times for Subnanosecond Gas Discharges at Pressures Below One Atmosphere, IEEE Transactions on Plasma Science 36, 2505 - 2511 (2008).
Abstract:  With a RADAN 303-A pulser (a rise time of 150 ps and a maximum voltage of 150 kV into matched load), fast breakdown in argon and air is investigated. An oil-filled coaxial transmission line is coupled with a lens to a biconical section and a radial millimeter-size gap operated at subatmospheric pressure. Diagnostics include capacitive voltage dividers which allow the determination of voltage across and current through the gap with a temporal resolution defined by the digitizer (20 Gs/s, 6 GHz) used. A scintillator-photomultiplier combination with different metal absorber foils and a temporal resolution of 2 ns is used as X-ray detector to obtain a rough energy spectrum of the X-rays and electrons in the range of 10-150 keV. Discharges are characterized by runaway electrons over much of the pressure range, with a strong excitation and ionization layer at the cathode surface, and ldquofree-fallrdquo conditions with negligible gaseous ionization for the rest of the gap. High-energy electrons (> 60 keV) are observed up to atmospheric pressure. Time-to-breakdown curves versus pressure have been measured for different applied voltage rise times. They resemble Paschen curves with a steep increase toward low pressure and a slow increase toward high pressure. The major experimental findings and particularly the time-to-breakdown curves are confirmed using simple force-equation modeling. Monte Carlo calculations simulating collisional ionizations and developing electron avalanches in three dimensions have been used to verify and explain the experimental results.

[PDF]

+ Compact Electro-Explosive Fuses for Explosive Driven Pulsed Power
  D. R. McCauley, D. W. Belt, J. J. Mankowski, J. C. Dickens, A. A. Neuber, and M. Kristiansen, "Compact Electro-Explosive Fuses for Explosive Driven Pulsed Power", to appear in IEEE Transactions on Plasma Science (2008)
Abstract:  Compact electroexplosive fuses (EEFs) as part of an explosively driven system are of interest for the one-time single-shot generation of high-power pulses. For instance, the transition from a very large driving current produced by an explosively driven flux compression generator (FCG), i.e., low impedance, to a large voltage spike delivered to the load, i.e., high impedance, can be done using an inductive storage system and an EEF. Typically, the EEF can be as large as, if not larger than, the current driver attached to it, thus making it one of the largest components in the system. Reduction in the size of the fuse will allow for size reductions of the entire high-power microwave (HPM) system. The goal of optimizing an EEF as an opening switch is to produce the greatest voltage multiplication possible to drive a load under physical size constraints. To optimize the fuse, several parameters are taken into account, including, but not limited to, fuse material, fuse length, fuse shape, and quenching medium. Individual optimization of these parameters will lead to complete optimization of an EEF, therefore resulting in a compact fuse capable of consistently producing maximum voltage multiplication for HPM systems.

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+ Effects of UV Illumination on Surface Flashover under Pulsed Excitation
  J. T. Krile, A. A. Neuber, H. G. Krompholz, "Effects of UV Illumination on Surface Flashover under Pulsed Excitation", to appear in IEEE Transactions on Plasma Science (2008)
Abstract:  Undesirable surface flashover of high voltage support structures can severely limit the compactness of open air high voltage systems. Only recently, increased effort has been invested in characterizing and quantifying the physical processes involved in surface flashover occurring under atmospheric conditions and under the influence of UV illumination. In this paper, a UV flash lamp and a solid-state UV source, with its much faster turn-off time, were utilized in conjunction with a high temporal resolution testing apparatus. The UV pulse, excitation voltage, discharge current, and flashover self-luminosity were measured with high temporal precision. We relate recent experiments to our experimental findings of surface flashover under atmospheric conditions gained over the past five years. A simple model that describes the observed behavior will be presented. In addition, a more advanced Monte Carlo-type code for electron collision dynamics will be utilized to further analyze the role of UV in surface flashover under atmospheric conditions.

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+ Fast-charging compact seed source for magnetic flux compression generators
  M. Elsayed, M. Kristiansen, A. Neuber, Fast-charging compact seed source for magnetic flux compression generators, 2008 Review of Scientific Instruments. Vol. 79, 124702.
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 kiloampere range for midsized 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 overvoltage 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 40 s), single-use compact seed source (CSS) using solid-state components for the switching scheme. The CSS 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 μH load with a trigger energy of microjoules 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. A 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.

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+ High Current Surface Flashover in a High Pressure SF6 Environment
  J. Krile, A. Neuber, R. Vela, "High Current Surface Flashover in a High Pressure SF6 Environment", to appear in IEEE Transactions on Plasma Science (2008)
Abstract:  A recent upgrade of Sandia National Laboratories' Z-machine has exposed a possible failure mode in the 5 MV laser-triggered gas switches (LTGS). During the closure of the cascade section of the switch, the surface flashover (SF) inside the dielectric switch housing occurred sporadically, affecting subsequent closing timing and damaging the switch housing. A small-scale experiment has been constructed to mimic conditions within the LTGS and to examine the survivability of various materials exposed to high-current SFs.

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+ High Power Microwave Switching Utilizing A Waveguide Spark Gap
  J. Foster, G. Edmiston, M. Thomas, A. Neuber, High Power Microwave Switching Utilizing A Waveguide Spark Gap, Rev. Sci. Instrum. 79, 114701 (2008).
Abstract:  A reduction in the rise time of a 2.85 GHz high power microwave (HPM) pulse is achieved by implementing an overvoltaged spark gap inside a waveguide structure. The spark gap is oriented such that when triggered, the major electric field component of the dominant TE10 mode is shorted. The transition from a transmissive to a highly reflective microwave structure in a relatively short period of time (tens of nanoseconds) creates a means to switch multimegawatt power levels on a much faster timescale than mechanical switches. An experimental arrangement composed of the waveguide spark gap and a high power circulator is used to reduce the effective rise time of a HPM pulse from a U.S. Air Force AW/PFS-6 radar set from 600 ns down to 50 ns. The resulting HPM pulse exhibits a much more desirable excitation profile when investigating microwave induced dielectric window flashover. Since most theoretical discussions on microwave breakdown assume an ideal step excitation, achieving a “squarelike” pulse is needed if substantial comparison between experiment and theory is sought. An overview of the experimental setup is given along with relevant performance data and comparison with computer modeling of the structure.

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+ High Power Microwave System
  T. Holt, A. Young, M. Elsayed, J. Walter, A. Neuber, and M. Kristiansen, "High Power Microwave System", to appear in IEEE Transactions on Plasma Science (2008)
Abstract:  Not Available
+ Images From the Development of a High-Power Microwave System
  T. Holt, A. Young, M. Elsayed, J. Walter, A. Neuber, and M. Kristiansen, Images From the Development of a High-Power Microwave System, IEEE Transactions on Plasma Science 36, 1414-1415 (2008).
Abstract:  A recently developed self-contained compact single-shot high-power microwave (HPM) system was tested and characterized. The explosive-driven system utilizes a reflex triode virtual cathode oscillator (vircator) as the HPM source. An open-shutter image acquired with a digital single-lens reflex camera during operation was used to show plasma development extending beyond the anode-cathode gap of the vircator. The plasma's self-emission is due to ionized material eroded and desorbed from both the cathode and the anode.

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+ Imaging of High Power Microwave Induced Surface Flashover on a Corrugated Dielectric Window
  G. Edmiston, J. Krile, A. Neuber, "Imaging of High Power Microwave Induced Surface Flashover on a Corrugated Dielectric Window", to appear in IEEE Transactions on Plasma Science (2008)
Abstract:  Dielectric window flashover is a severe pulse-shortening phenomenon limiting the power levels radiated in high power microwave (HPM) systems. This type of flashover develops in regions under high field stress coinciding with the dielectric interfaces separating the vacuum and atmospheric pressure sections of a microwave system. The formation of plasma at the exit aperture of a transmitting system can have several detrimental effects, including premature termination of the radiated pulse and/or the reflection of potentially damaging levels of radiation back toward the microwave source. Experimental studies of HPM surface flashover have been conducted under a variety of conditions in the S-band at power levels up to 5 MW with the aim of quantifying the relative impact of parameters such as gas pressure, type, and window geometry. One particular geometry variant designed with grooves perpendicular to the major electric field component at the window surface exhibited superior flashover suppression characteristics when compared with smooth window geometries. Images of HPM surface flashover evolution on this corrugated dielectric window geometry are presented.

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+ Imaging of the Explosive Emission Cathode Plasma in a Vircator High-Power Microwave Source
  Walter, J.; Mankowski, J.; Dickens, J.; Imaging of the Explosive Emission Cathode Plasma in a Vircator High-Power Microwave Source; Plasma Science, IEEE Transactions on Volume 36, Issue 4, Part 1, Aug. 2008 Page(s):1388 - 1389 Digital Object Identifier 10.1109/TPS.2008.924489
Abstract:  Most pulsed high-power microwave sources use explosive electron emission cathodes to generate high current electron beams. In the explosive emission process, the current emitted through small field emission points becomes high enough to cause the cathode material to vaporize and form a plasma. Plasma characteristics, such as uniformity and expansion rate, will affect the performance of the microwave source. High-speed optical imaging can be used to resolve some characteristics of the plasma in time. The images of the cathode plasma during the operation of a triode-geometry virtual cathode oscillator high-power microwave source are presented for three different cathode materials.

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+ Impact of Volume Breakdown on Surface Flashover in High Pressure SF6
  A. Neuber, J. Krile, G. Rogers, H. Krompholz, "Impact of Volume Breakdown on Surface Flashover in High Pressure SF6,", Acta Physica Polonica 115, 995-997 (2008)
Abstract:  Not Available
+ Low-Jitter Triggered Spark Gap With High-Pressure Gas Mixtures
  Yeong-Jer Chen; Mankowski, J.J.; Dickens, J.C.; Walter, J.; Kristiansen, M.; Low-Jitter Triggered Spark Gap With High-Pressure Gas Mixtures; Plasma Science, IEEE Transactions on Volume 36, Issue 5, Part 3, Oct. 2008 Page(s):2546 - 2553 ; Digital Object Identifier 10.1109/TPS.2008.2004366
Abstract:  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 ultralow 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 that 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 30 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 >100-kV 10-ns rise-time pulses at a rep rate of 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. Switch operations in 30 kV and 10 Hz have shown reliable subnanosecond 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 data collected for each of the pure gases. Recovery was monitored with no major problems at the 100-Hz operation, and subnanosecond jitter results for H2 , N2, and SF6 are also recorded.

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+ Secondary Arc Formation Within a Distributed Energy Railgun
  Karhi, R.W.; Mankowski, J.J.; Dickens, J.C.; Kristiansen, M.; Wetz, D.A.; Secondary Arc Formation Within a Distributed Energy Railgun; Plasma Science, IEEE Transactions on Volume 36, Issue 5, Part 3, Oct. 2008 Page(s):2738 - 2746 Digital Object Identifier 10.1109/TPS.2008.2004228
Abstract:  Experimental results comparing a breech-fed scheme and two distributed energy schemes for a free-running arc are presented. Analysis and observations of the issues associated with distributed energy switching of a plasma arc in the railgun are explored. The use of a free-running arc allows experiments to emulate the ablation and restrike phenomenon of a plasma armature railgun at high speeds (> 5 km/s) without the requirement of a large amount of stored energy. Numerous experimental tests were conducted to investigate the dynamics of plasma arcs within a distributed energy source railgun. Variations of switch timing, bore pressure, bore material, current amplitude, and current pulse length within each stage have been tested. These data reveal important design parameters for distributed energy railguns. The arc length, stage length, and stage trigger timing play a crucial role in distributed energy railgun performance. Failure to take these parameters into consideration will result in velocity reduction through plasma arc restrike and/or splitting.

[PDF]

+ Seed Electron Production from O- Ions under High Power Microwave Excitation
  G. F. Edmiston, A. A. Neuber, H. G. Krompholz, J. T. Krile, "Seed Electron Production from O- Ions under High Power Microwave Excitation", J. Appl. Phys. 103, 063303 (2008)
Abstract:  Surface and volume breakdown formation during pulsed high-power microwave (HPM) excitation can severely limit the power densities which can be transmitted into an atmospheric medium. Recent studies in this area have focused on developing models which accurately predict flashover formation at either dielectric/air interfaces or in the gas volume directly adjacent to these interfaces. These models are typically validated through comparison with experimentally gathered data. With respect to HPM surface flashover, experiments 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. A Monte Carlo-type electron motion simulation code, MC, has been developed to calculate the increasing electron density during flashover formation in this case. Results from the MC 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 ultraviolet 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 often assumed to be 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 toward predicting HPM flashover over a wide range of parameters, particularly in the presence of highly electronegative gases such as SF6 or O2, in which there is an absence of free electrons with zero applied field.

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+ Utilization of a Nonexplosive Test Bed for Flux-Compression-Generator Electroexplosive Opening Switches
  D. W. Belt, J. J. Mankowski, A. A. Neuber, J.C. Dickens, M. Kristiansen, Utilization of a Nonexplosive Test Bed for Flux-Compression-Generator Electroexplosive Opening Switches, IEEE Transactions on Plasma Science 36, 2684 - 2690, (2008).
Abstract:  Helical flux compression generators (HFCGs) 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-muH inductor. One way to drive a high-power microwave source with an HFCG is by power conditioning, such as an inductive energy storage system (IESS). The output performance of the IESS is contingent upon the opening switch scheme, usually an electroexplosive fuse. Our previous work involving fuse parameter characterization has established a baseline for potential fuse performance. In order to optimize the electroexplosive wire fuse, we have constructed a nonexplosive 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 use of the nonexplosive HFCG test bed will allow the verification of scalability of the fuse parameter model and also allow testing of exotic fuse materials. The nonexplosive test bed has provided a more efficient method for electroexplosive switch development and has allowed us to expand the study of opening switches. We will also 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.

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Publication Year:  2007
+ A Bench Top Railgun With Distributed Energy Sources
  Mankowski, J.; Dickens, J.; Giesselmann, M.; McDaniel, B.; McHale, B.; Kristiansen, M.; IEEE Transactions on Magnetics, Volume 43, Issue 1, Part 2, Jan. 2007 Page(s):167 - 169
Abstract:  Experimental results of a distributed energy source railgun are presented. Distributed energy source railguns were first proposed by Marshal in an asynchronous scheme and later by Parker synchronously. Both schemes employ a "traveling excitation wave" to push the projectile along the rail. The primary advantages of such a scheme over the common breech-fed is higher efficiency due to less energy remaining in the rail and lower rail resistive loses. Another advantage is the reduction in the probability of re-strike. However, these advantages are achieved at a cost of higher switching complexity. As a proof of principle experiment, we have constructed a bench-top solid armature railgun with distributed energy sources. Instead of a single, capacitive, breech-fed, energy source, the current is supplied by two storage capacitor banks, placed at different positions along the rail. The switching configuration, which requires a dedicated switch at each capacitor, is realized with sold state switches. The railgun is diagnosed in order to evaluate performance and to appropriately trigger the switches. In addition, experimental results are compared to simulation

[PDF]

+ Cathode and Anode Optimization in a Virtual Cathode Oscillator
  Chen, Y.; Mankowski, J.; Walter, J.; Kristiansen, M.; Gale, R.; IEEE Transactions on Dielectrics and Electrical Insulation, [see also IEEE Transactions on Electrical Insulation] Volume 14, Issue 4, Aug. 2007 Page(s):1037 - 1044
Abstract:  Not Available

[PDF]

+ Contributing Factors to Window Flashover Under Pulsed High Power Microwave Excitation at High Altitude
  G. Edmiston, A. Neuber, L. McQuage, J. Krile, H. Krompholz, J. Dickens, "Contributing Factors to Window Flashover Under Pulsed High Power Microwave Excitation at High Altitude", IEEE Transactions on Dielectrics and Electrical Insulation 14, pp. 783-789 (2007)
Abstract:  One of the major limiting factors for the transmission of high power microwave (HPM) radiation is the interface between dielectric-vacuum or even more severely between dielectric-air if HPM is to be radiated into the atmosphere. Surface flashover phenomena which occur at these transitions severely limit the power levels which can be transmitted. It is of major technological importance to predict surface flashover events for a given window geometry, material and power level. When considering an aircraft based high power microwave platform, the effects on flashover formation due to variances in the operational environment corresponding to altitudes from sea level to 50,000 feet (760 to 90 Torr; 1 Torr=133.3 Pa) are of primary interest. The test setup is carefully designed to study the influence of each atmospheric variable without the influence of high field enhancement or electron injecting metallic electrodes. Experimental data of flashover delay times across different materials, such as polycarbonate, Teflonreg, and high density polyethylene as a function of background pressure and gas type, air, N2, argon are discussed. An empirical relationship between flashover field amplitude and delay time is given.

[PDF]

+ Dielectric Surface Flashover at Atmospheric Conditions with Unipolar Pulsed Voltage Excitation
  Morales, K.; Krile, J.; Neuber, A.; Krompholz, H.; IEEE Transactions on Dielectrics and Electrical Insulation, [see also IEEE Transactions on Electrical Insulation], Volume 14, Issue 4, Aug. 2007 Page(s):774 - 782
Abstract:  Not Available

[PDF]

+ IEEE Transactions on Dielectrics and Electrical Insulation
  G. Edmiston, A. Neuber, L. McQuage, J. Krile, H. Krompholz, J. Dickens, IEEE Transactions on Dielectrics and Electrical Insulation, Volume: 14 , Issue: 4, Page(s): 783 - 789
Abstract:  Not Available
+ Interface Breakdown During High-Power Microwave Transmission
  Neuber, A. A.; Edmiston, G. F.; Krile, J. T.; Krompholz, H.; Dickens, J. C.; Kristiansen, M.; IEEE Transactions on Magnetics, Volume 43, Issue 1, Part 2, Jan. 2007 Page(s):496
Abstract:  The major limiting factor in the transmission of narrowband high-power microwaves (HPM) has been the interface between vacuum-vacuum or even more severely between vacuum-air if HPM are to be radiated into the atmosphere. Extensive studies have identified the physical mechanisms associated with vacuum/dielectric flashover, as opposed to the mechanisms associated with dielectric/air flashover, which are not as well known. Due to the high electron collision frequencies (in the terahertz range) with the background gas molecules, established mitigation methods and concepts of vacuum/dielectric flashover will have to be re-evaluated. The primarily limiting factors of HPM transmission through a dielectric/air interface are presented based on recent experiments at 2.85 GHz. The physics of the involved mechanisms and their practical ramifications are discussed. The potential of surface roughness/geometry for flashover mitigation is addressed as

[PDF]

+ Jitter and Recovery Rate of a Triggered Spark Gap with High Pressure Gas Mixtures
  Yeong-Jer Chen; Mankowski, J.J.; Walter, J.W.; Dickens, J.C.; Jitter and Recovery Rate of a Triggered Spark Gap with High Pressure Gas Mixtures; Pulsed Power Plasma Science, 2007. PPPS 2007. Conference Record - Abstracts. IEEE 17-22 June 2007 Page(s):255 - 25
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.

[PDF]

+ Pulsed Dielectric Surface Flashover in an SF6 Environment
  J. T. Krile, R. Vela, A. A. Neuber, and H. G. Krompholz, "Pulsed Dielectric Surface Flashover in an SF6 Environment", IEEE Transactions on Plasma Science 35, pp. 1580-1587 (2007)
Abstract:  A recently upgraded laser-triggered gas switch at Sandia National Laboratories has developed a failure mode that results in the breakdown spark tracking to the inside of the containment envelope. These breakdowns along the surface, or surface flashovers, degrade the performance of the overall switch, causing the switch to prefire in the successive shot. In the following, experimental results of pulsed surface flashover across different dielectric materials in SF6, primarily at atmospheric pressure, as well as flashover and volume breakdown in at pressures from 1.3 to 365.4 kPa are presented. In addition to fast voltage and current monitoring of the breakdown event, an increased emphasis was put on imaging the event as well as gathering optical emission spectra (~200-700 nm) from it. As much as possible, the small-scale experiments were designed to reproduce, at least partly, the conditions as they are found in the large 5-MV switch. An effort was made to determine what changes could be made to reduce the occurrence of surface flashovers, in addition to some broadly applicable conclusions on surface flashovers in an SF6 environment.

[PDF]

+ Spectral Analysis of Pulsed Volume Breakdown in SF6 at High Pressures
  Krile, J. T.; Vela, R.; Neuber, A. A.; Krompholz, H. G.; IEEE Transactions on Plasma Science, Volume 35, Issue 4, Part 3, Aug. 2007 Page(s):1163 - 1169
Abstract:  The Z-machine, which is located at Sandia National Laboratories, is currently undergoing refurbishment to increase the output drive current. Due to increased switching voltage requirements, some switch failure modes have been identified with the laser-triggered gas switch design, including envelope surface flashover. In order to improve the performance and lifetime of these switches, a basic understanding of the underlying physics of the failure mechanisms is required. A small-scale experimental setup has been constructed to approximate conditions within the switch. The possible impact of the $hbox{SF}_{6}$ volume spark between the switch electrodes on the envelope surface flashover is investigated. Measured optical spectra of the $ hbox{SF}_{6}$ volume spark over a wide pressure range, from rough vacuum to 40 psig overpressure, are analyzed regarding their potential to contribute to switch failure

[PDF]

Publication Year:  2006
+ Conduction and breakdown mechanisms in transformer oil
  M Butcher, AA Neuber, MD Cevaolls, JC Dickens, H Krompholz, "Conduction and breakdown mechanisms in transformer oil" Plasma Science, IEEE Transactions on 34 (2), 467-475
Abstract:  Not Available
+ Conduction and breakdown mechanismsin transformer oil
  M Butcher, AA Neuber, MD Cevallos, JC Dickesn, H Krompholz, "Conduction and breakdown mechanismsin transformer oil" Plasma Science, IEEE Transactions on 34 (2), 467-475
Abstract:  Not Available
+ Conduction and breakdown mechanismsin transformer oil
  Butcher, M.; Neuber, A.A.; Cevallos, M.D.; Dickens, J.C.; Krompholz, H.; IEEE Transactions on Plasma Science, Volume 34, Issue 2, Part 3, April 2006 Page(s):467 - 475
Abstract:  With a fast coaxial test setup using high speed electrical and optical diagnostics, prebreakdown current pulses and shadowgraphy images are measured for direct current (dc) breakdown in Univolt 61 transformer oil. Also, dc currents across the gap are measured using a high sensitivity electrometer. The conduction and breakdown mechanisms in transformer oil as function of applied hydrostatic pressures are quantified. Together, this information provides data on the development of current flow in the system. We have identified three stages in the conduction process prior to breakdown for highly nonuniform fields. Stage 1 is characterized by a resistive current at low fields. Increasing the applied electric field lowers the effective barrier at the metal/dielectric interface allowing a "tunneling" mechanism to begin, leading to the rapid rise in the injection current observed in stage 2. In stage 3, at high fields, the current reaches space charge saturation with an apparent mobility of 3/spl middot/10/sup -3/ cm/sup 2//V/spl middot/s prior to breakdown. The processes of final breakdown show a distinct polarity dependence. A strong pressure dependence of the breakdown voltage is recorded for negative needle/plane breakdown; a 50% reduction in breakdown voltage is observed when the hydrostatic pressure is lowered from atmospheric pressure to hundreds of mtorr. Positive needle discharges show a reduction of only about 10% in breakdown voltage for the reduced pressure case. Weak pressure dependence indicates the breakdown mechanism does not have a strong gaseous component. We will discuss possible links between conduction current and dc breakdown.

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+ Design and implementation of a flux compression generator nonexplosive test bed for electroexplosive fuses
  D Belt, J Mankowski, A Neuber, J Dickens, M Kristiansen, "Design and implementation of a flux compression generator nonexplosive test bed for electroexplosive fuses" Review of scientific instruments 77, 094702
Abstract:  Not Available
+ Design and implementation of a flux compression generator nonexplosive test bed for electroexplosive fuses
  D. Belt, J. Mankowski, A. Neuber, J. Dickens, and M. Kristiansen Center for Pulsed Power and Power Electronics, Texas Tech University, Lubbock, Texas 79409-3102; Departments of Electrical, Texas Tech University, Lubbock, Texas 79409-3102; and Computer Engineering and Physics, Texas Tech University, Lubbock, Texas 79409-3102 Review of Scientific Instruments, Vol 77, Article 094702 (2006) (7 pages)
Abstract:  Helical flux compression generators (HFCGs) 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 µH inductor. By utilizing an electroexplosive fuse, a large dI/dt into a coupled load is possible. Our previous work with a nonoptimized fuse has produced ~100 kV into a 15 load, which leads into a regime relevant for high power microwave systems. It is expected that ~300 kV can be achieved with the present two-stage HFCG driving an inductive storage system with electroexploding fuse. In order to optimize the electroexplosive wire fuse, we have constructed a nonexplosive 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 four stages of inductance change and is based upon a piecewise linear regression model of the HFCG wave form. The nonexplosive test bed will provide a more efficient method of component testing and has demonstrated positive initial fuse results. By utilizing the nonexplosive test bed, we hope to reduce the physical size of the inductive energy storage system and fuse substantially. ©2006 American Institute of Physics

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+ High-Power Microwave Surface Flashover of a Gas&# 8211; Dielectric Interface at 90&# 8211; 760 torr
  G Edminston, J Krile, A Neuber, J Dickens, H Krompholz, "High-Power Microwave Surface Flashover of a Gas&# 8211; Dielectric Interface at 90&# 8211; 760 torr" Plasma Science, IEEE Transactions on 34 (5), 1782-1788
Abstract:  Not Available
+ High-Power Microwave Surface Flashover of a Gas-Dielectric Interface at 90-760 torr
  Edmiston, G.; Krile, J.; Neuber, A.; Dickens, J.; Krompholz, H.; IEEE Transactions on Plasma Science, Volume 34, Issue 5, Part 1, Oct. 2006 Page(s):1782 - 1788
Abstract:  The major limiting factor in the transmission of high-power microwave (HPM) has been the interface between dielectric–vacuum or, even more severely, between dielectric–air, if HPM is to be radiated into the atmosphere. Extensive studies have identified the physical mechanisms associated with vacuum–dielectric flashover, as opposed to the mechanisms associated with air–dielectric flashover, which are not as well known. Surface-flashover tests involving high field enhancement due to the presence of a triple point have shown that volume breakdown threshold (dielectric removed) is approximately 50% higher than the flashover threshold with a dielectric interface over the 90–760 torr range. In order to quantify the role of field enhancement in the flashover process independent of electron injection from metallic surfaces, the effects of the triple point are minimized by carefully choosing the geometry, and in some cases, the triple point is “removed” from the flashover location. Experimental results were presented, including the impact of gas pressure and the presence of UV illumination, along with temperature analysis of the developing discharge plasma and temporally resolved images of the flashover formation. These results are compared with literature data for volume breakdown in air, with discussion on the similarities and differences between the data.

[PDF]

+ Monte Carlo simulation of HPM window breakdown at atmospheric conditions
  John T. Krile, Andreas A. Neuber, Hermann G. Krompholz, and Thomas L. Gibson, Monte Carlo simulation of HPM window breakdown at atmospheric conditions. Applied Physics Letters vol. 89, 201501 (2006).
Abstract:  Not Available
+ Phenomenology of subnanosecond gas discharges at pressures below one atmosphere
  HG Krompholz, LL Hatfield, AA Neuber, KP Kohl, JE Chaparro, HY Ryu, "Phenomenology of subnanosecond gas discharges at pressures below one atmosphere" Plasma Science, IEEE Transactions on 34 (3), 927-936
Abstract:  Not Available
+ Phenomenology of subnanosecond gas discharges at pressures below one atmosphere
  Krompholz, H.G.; Hatfield, L.L.; Neuber, A.A.; Kohl, K.P.; Chaparro, J.E.; Han-Yong Ryu; IEEE Transactions on Plasma Science, Volume 34, Issue 3, Part 3, June 2006 Page(s):927 -
Abstract:  Volume breakdown and surface flashover in quasi-homogeneous applied fields in 10/sup -5/ to 600 torr argon and dry air are investigated, using voltage pulses with 150 ps risetime, <1ns duration, and up to 150 kV amplitude into a matched load. The test system consists of a transmission line, a transition to a biconical section, and a test gap, with gap distances of about 1mm. The arrangement on the other side of the gap is symmetrical. Diagnostics include fast capacitive voltage dividers, for determination of voltage waveforms in the gap, and conduction current waveforms through the gap. X-ray diagnostics use a scintillator-photomultiplier combination with different absorber foils yielding coarse spectral resolution. Optical diagnostics include use of a streak camera to get information on the discharge channel geometry and dynamics, and temporally resolved measurements with photomultipliers. Breakdown delay times are on the order of 100-400 ps, with minima occurring in the range of several 10torr. X-ray emission extends to pressures >100 torr, indicating the role of runaway electrons during breakdown. Maximum X-ray emission coincides with shortest breakdown delay times at several 10 torr. Simple modeling using the average force equation and cross sections for momentum transfer and ionization supports the experimental results

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+ Pulsed dielectric surface flashover in nitrogen at atmospheric conditions
  Morales, K.P.; Krile, J.T.; Neuber, A.A.; Krompholz, H.G.; IEEE Transactions on Dielectrics and Electrical Insulation, Volume 13, Issue 4, Aug. 2006 Page(s):803 - 809
Abstract:  Dielectric flashover along insulators in vacuum has been comprehensively researched in the past. Less studied, but of similar importance, is surface flashover at atmospheric pressures and the impact of an atypical electrode geometry, humidity, and ultraviolet (UV) illumination. Previous research has shown distinct discharge behavior in air and nitrogen environments for an electrode geometry in which the applied electric field lines curve above the dielectric surface. It was concluded that the discharge development path, whether along the electric field lines 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 discharge’s production of UV radiation in an oxygen rich environment. Thus, experiments were conducted in a nitrogen environment employing UV surface illumination in order to observe the affects on the flashover spark behavior. From the experimental data, it can be ascertained that UV illumination and intensity play a significant role in the discharge development path. Based on these results an explanation of the physical mechanisms primarily involved in unipolar surface flashover will be presented. Additional experiments regarding the effects of humidity on the discharge behavior will be discussed as well.

[PDF]

+ Pulsed dielectric surface flashover in nitrogen at atmospheric conditions
  KP Morales, JT Krile, AA Neuber, HG Krompholz, "Pulsed dielectric surface flashover in nitrogen at atmospheric conditions" Dielectrics and Electical Insulation, IEEE Transactions on 13 (4), 803-809
Abstract:  Not Available
+ Pulsed power technology development at Sandia.
  Dillon Heirman McDaniel, David Emery Bliss, Keith R LeChien, Larry Kevin Warne, James Albert Van Den Avyle, Kenneth William Struve, Andreas A Neuber, Kenneth Randel Prestwich, Joseph Ray Woodworth, Jane Marie Lehr, Keith Conquest Hodge, John Phillip Corley, Peter Eric Wakeland, Scott J MacGregor, Richard Miller, Randy McKee, John Eric Maenchen, Scott Kovaleski, Mark Edward Savage, David L Johnson, "Pulsed power technology development at Sandia." Sandia National Laboratories.
Abstract:  Not Available
+ Similarities Of Dielectric Surface Flashover at Atmospheric Conditions for Pulsed Unipolar and RF Excitation
  J. Krile, G. Edmiston, K. Morales, A. Neuber, H. Krompholz, and M. Kristiansen, Similarities Of Dielectric Surface Flashover at Atmospheric Conditions for Pulsed Unipolar and RF Excitation, Laser Physics in Special Issue "Plasma, Beams, and Lasers" Dedicated to Professor Gennady A. Mesyats on his 70th Birth Anniversary, vol. 16, pp. 194-201, 2006.
Abstract:  Not Available
+ Similarities of dielectric surface flashover under atmospheric conditions for pulsed unipolar and RF excitation
  J Krile, G Edmiston, K Morales, A Neuber, H Krompholz, M Kristiansen, "Similarities of dielectric surface flashover under atmospheric conditions for pulsed unipolar and RF excitation" Laser Physics 16 (1), 194-201
Abstract:  Not Available
+ The Impact of Field Enhancements and Charge Injection on the Pulsed Breakdown Strength of Water
  Wetz, D.A.; Mankowski, J.J.; Dickens, J.C.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 34, Issue 5, Part 1, Oct. 2006 Page(s):1670 - 1679
Abstract:  A unique theoretical model of the breakdown mechanism in water has been developed and further tested in both simulation software and experimentation. The conducted experiments test the degree to which electrode material, surface roughness, and surface area impact the dielectric strength of water. Voltage pulses with respective rise times of roughly 200 and 20 ns were applied to a water test gap producing electric fields in excess of 1.5 MV/cm. In experiments testing various electrode materials, thin film coatings of various metallic alloys and oxides were applied to Bruce-profiled stainless steel electrodes, with an effective area of 5$hboxcm^2$, through ion beam deposition. Similar Bruceprofiled stainless steel electrodes with surface roughness ranging from 0.26 to 1.96$muhboxm$and effective areas ranging from 0.5 to 75$hboxcm^2$were used in the study of surface roughness and area. Additionally, shadowgraph images of a point plane geometry were taken to further understand the breakdown processes that occur.

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Publication Year:  2005
+ 5.1 Shocked Gases within the Flux Compression Generator Volume
  BL Freeman, AA Neuber, "5.1 Shocked Gases within the Flux Compression Generator Volume" Explosively Driven Pulsed Power: Helical Magnetic Flux Compression Generators 127
Abstract:  Not Available
+ 8.1 Seed Sources Basic
  JC Dickens, AA Neuber, "8.1 Seed Sources Basic" Explosively driven pulsed power: helical magnetic flux compression generators
Abstract:  Not Available
+ DC and pulsed dielectric suface flashover at atmospheric pressure
  JT Krile, AA Neuber, JC Dickens, HG Krompholz, "DC and pulsed dielectric suface flashover at atmospheric pressure" Plasma Science, IEEE Transactions on 33 (4), 1149-1154
Abstract:  Not Available
+ DC and Pulsed Dielectric Surface Flashover at Atmospheric Pressure
  Krile, J.T.; Neuber, A.A.; Dickens, J.C.; Krompholz, H.G.; IEEE Transactions on Plasma Science, Volume 33, Issue 4, Part 1, Aug. 2005 Page(s):1149 - 1154
Abstract:  In a wide variety of high-voltage applications surface flashover plays a major role in the system's performance and yet has not been studied in great detail for atmospheric conditions with modern diagnostic tools. Environmental conditions to be considered include pressure, humidity, and gas present in the volume surrounding the dielectric. In order to gain knowledge into the underlying process involved in dielectric surface flashover, a setup has been created to produce and closely monitor the flashover event. Surface flashover for both direct current and pulsed voltages is considered. Within the setup, parameters such as geometry, material, and temporal characteristics of the applied voltage can be altered. Current, voltage, and luminosity are measured with nanosecond to sub-nanosecond resolution. Previously measured optical emission spectra is also discussed.

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+ Design and optimization of a compact, repetitive, high-power microwave system
  Y. J. Chen, A. A. Neuber, J. Mankowski, J. C. Dickens, and M. Kristiansen Texas Tech University, Center for Pulsed Power and Power Electronics, Lubbock, Texas 79409-3102 R. Gale Texas Tech University, Nano Tech Center, Lubbock, Texas 79409-3102 Review of Scientific Instruments, Vol 76, Article 104703 (2005) (8 pages)
Abstract:  The electrical characteristics and design features of a low inductance, compact, 500 kV, 500 J, 10 Hz repetition rate Marx generator for driving an high-power microwave (HPM) source are discussed. Benefiting from the large energy density of mica capacitors, four 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 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 virtual cathode oscilator (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. Design and testing of a low cost, all-metal Vircator cathode will also be discussed. ©2005 American Institute of Physics

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+ Design and optimization of a compact, repetitive, high-power microwave system
  YJ Chen, AA Neuber, J Mankowski, JC Dickens, M Kristiansen, R Gale, "Design and optimization of a compact, repetitive, high-power microwave system" Review of scientific instruments 76, 104703
Abstract:  Not Available
+ Fast, transient energy extraction from high-frequency AC alternators for use in electromagnetic launch applications
  M Giesselman, B McHale, M Crawford, "Fast, transient energy extraction from high-frequency AC alternators for use in electromagnetic launch applications" Magnetics, IEEE Transactions on 41 (1), 289-293
Abstract:  Not Available
+ Generator Modeling
  M Giesselmann, I Smith, B Novac, A Neuber, "Generator Modeling", Explosively Driven Pulsed Power, 159-199
Abstract:  Not Available
+ Guest Editorial Special Issue on Power Modulators and Repetitive Pulsed Power
  Kirkici, H.; Neuber, A.; Umstattd, R.J.; IEEE Transactions on Plasma Science, Volume 33, Issue 4, Part 1, Aug. 2005 Page(s):1134 - 1135
Abstract:  Not Available

[PDF]

+ Guest Editorial Special Issue on Power Modulators and Repetitve Pulsed Power
  H Kirkici, A Neuber, RJ Rmstattd, "Guest Editorial Special Issue on Power Modulators and Repetitve Pulsed Power" Plasma Science, IEEE Transactions on 33 (4), 1134-1154
Abstract:  Not Available
+ Imaging of dielectric surface flashover in atmospheric conditions
  Krile, J.; Neuber, A.; Dickens, J.; Krompholz, H.; IEEE Transactions on Plasma Science, Volume 33, Issue 2, Part 1, Apr 2005 Page(s):270 - 271
Abstract:  Using a gated intensified digital charge coupled device (ICCD) camera, the development of flashovers across a dielectric surface has been imaged in various gasses at atmospheric pressures. The arc displayed a strong tendency to develop close to the surface, as opposed to following the electric field line leading away from the surface, when oxygen is present in the environment. These findings along with spectroscopy data help to yield a better understanding of the processes involved in surface flashover.

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+ Imaging of negative polarity dc breakdown streamer expansion in transformer oil due to variations in background pressure
  Cevallos, M.D.; Butcher, M.; Dickens, J.; Neuber, A.; Krompholz, H.; IEEE Transactions on Plasma Science, Volume 33, Issue 2, Part 1, April 2005 Page(s):494 - 495
Abstract:  The breakdown physics of transformer oil is investigated using high speed electrical and optical diagnostics. Experiments are done in self-breakdown mode utilizing a needle/plane geometry. Shadowgraphy combined with high-speed electrical diagnostics are aimed at measuring streamer expansion as a function of external pressure. Assuming a breakdown mechanism for negative needle based on bubble formation with subsequent carrier amplification in the gas phase implies a pressure dependence, which is observed in the experiments, i.e. the expansion velocity decreases with increasing pressure.

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+ Microbubble-based model analysis of liquid breakdown initiation by a submicrosecond pulse
  J. Qian, R. P. Joshi, J. Kolb, and K. H. Schoenbach, J. Dickens, A. Neuber, M. Butcher, M. Cevallos, and H. Krompholz, E. Schamiloglu and J. Gaudet, "Microbubble-based model analysis of liquid breakdown initiation by a submicrosecond pulse," J. Appl. Phys. 97, 113304, 2005.
Abstract:  Not Available
+ Power Conditioning
  T Heeren, M Giesselmann, A Neuber, "Power Conditioning" Explosively Dirven Pulsed Power, 201-233
Abstract:  Not Available
+ The Impact of Surface Conditioning and Area on the Pulsed Breakdown Strength of Water
  Wetz, D.A., Jr.; Truman, K.P.; Mankowski, J.J.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 33, Issue 4, Part 1, Aug. 2005 Page(s):1161 - 1169
Abstract:  Experimental results are presented on the degree to which electrode surface conditioning and surface area impact the dielectric strength of water. The applied pulse to the test gap reached electric field levels greater than 1.5 MV/cm with risetimes around 200 and 50 ns, respectively. The test gap is composed of 304 stainless steel electrodes machined with a Bruce profile. Electrode surface roughness ranged from 0.34 to 1.41$muhbox m$and effective areas ranged from 0.5 to 75$hbox cm^2$. Additional results are presented on the pulsed breakdown strength of Rexolite with various surface finishes ranging from .025 to 5.715$muhbox m$. Conclusions are made as to the effect electrode surface area and surface roughness has on the holdoff voltage of water dielectric systems. Conclusions are also made as to the impact of the surface condition of Rexolite has on its bulk breakdown strength.

[PDF]

Publication Year:  2004
+ Approximate Analytical Solitopms for the Space-Charge-Limited Current in One-Dimensional and Two-Dimensional Cylindrical Diodes
  "Approximate Analytical Solitopms for the Space-Charge-Limited Current in One-Dimensional and Two-Dimensional Cylindrical Diodes", Physics of Plasmas, 11, 6 3278-3283, June 2004 (with James Dickesn, L.L. Hatfield, and Eun-Ho Choi).
Abstract:  Not Available
+ Approximate Analytical Solutions for the Space-Charge-Limited Current in One-Dimensional and Two-Dimensional Cylindrical Diodes
  "Approximate Analytical Solutions for the Space-Charge-Limited Current in One-Dimensional and Two-Dimensional Cylindrical Diodes", Physics of Plasmas, June 2004 11 6, 3278-3283, (with James Dickens, L.L. Hatfield, and Eun-Ho Choi).
Abstract:  Not Available
+ DC flashover of a dielectric surface in atmospheric conditions
  Krile, J.T.; Neuber, A.A.; Dickens, J.C.; Krompholz, H.G.; IEEE Transactions on Plasma Science, Volume 32, Issue 5, Part 1, Oct. 2004 Page(s):1828 - 1834
Abstract:  Surface flashover is a major consideration in a wide variety of high-voltage applications, and yet has not been studied in great detail for atmospheric conditions, with modern diagnostic tools. Environmental conditions to be considered include pressure, humidity, and gas present in the volume surrounding the dielectric. In order to gain knowledge into the underlying process involved in dielectric surface flashover, a setup has been created to produce and closely monitor the flashover event. Within the setup parameters such as geometry, material, and temporal characteristics of the applied voltage can be altered. Current, voltage, luminosity, and optical emission spectra are measured with nanosecond to subnanosecond resolution. Spatially and temporally resolved light emission data is also gathered along the arc channel. Our fast imaging data show a distinct trend for the spark in air to closely follow the surface even if an electrical field with a strong normal component is present. This tendency is lacking in the presence of gases such as nitrogen, where the spark follows more closely the electric field lines and develops away from the surface. Further, the breakdown voltage in all measured gases decreases with increasing humidity, in some cases as much as 50% with an increase from 10% relative humidity to 90% relative humidity.

[PDF]

+ Guest Editorial Fifth Special Issue on Pulsed Power Science and Technology
  Dickens, J.C.; Lehr, J.M.; Mankowski, J.; IEEE Transactions on Plasma Science, Volume 32, Issue 5, Part 1, Oct. 2004 Page(s):1763 - 1764
Abstract:  Not Available

[PDF]

+ High Power Microwave Breakdown of Gas-Dielectric Interface at 90 to 760 Torr
  G Edmistion, A Neuber, H Krompholz, J Dickens, "High Power Microwave Breakdown of Gas-Dielectric Interface at 90 to 760 Torr" APS Meeting Abstracts 1, 1011
Abstract:  Not Available
+ Magnetic flux compression Generators
  Neuber, A.A.; Dickens, J.C.; Proceedings of the IEEE Volume 92, Issue 7, July 2004 Page(s):1205 - 1215
Abstract:  Magnetic flux compression generators offer the largest pulsed power output per unit size or weight when compared with other more conventional systems. They have found widespread use as pulsed power sources for hydrodynamics programs and high magnetic field research at national laboratories or in commercial applications, including exploration for oil and minerals and mine detection. Also, due to their nature as a true one-time-use device with superior energy density, a large portion of applications is defense related. A variety of basic magnetic flux compression generator designs have been developed and tested during the past four decades. All of them rely on the explosive-driven deformation of a system of conductors having an initial, preferably large, inductance. The most successful basic design is the helical flux compression generator, which is capable of producing a high-energy output into large impedance loads, just as it is needed for a practical pulsed power source. This paper will review the advances and state of the art of primarily helical magnetic flux compression generators mainly developed as pulsed power sources and will offer new insights gained as a result of a recently completed five-year AFOSR/DoD Multidisciplinary University Research Initiative program that studied the basic physics and engineering aspects of helical flux compression generators

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+ Microwave frequency determination mechanisms in a coaxial vircator
  Xupeng Chen; Dickens, J.; Mankowski, J.; Hatfield, L.L.; Eun Ha Choi; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 32, Issue 5, Part 1, Oct. 2004 Page(s):1799 - 1804
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. In this paper, some experiments showing different results are reported. In particular, the E-beam is observed to play 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 with different geometries has been investigated in detail. Investigation of the E-beam performance will improve understanding of the interaction between the E-beam and microwaves, which is a key for determining the microwave frequency. These results are helpful in optimizing the design of a cylindrical diode to avoid microwave frequency shifting and mode competition.

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+ Modern Pulsed Power: Charlie Martin and Beyond
  Schamiloglu, E.; Barker, R.J.; Gundersen, M.; Neuber, A.A.; Proceedings of the IEEE on Pulsed Power Technology, Volume 92, Issue 7, July 2004 Page(s):1014 - 1020
Abstract:  In this introduction to the Special Issue on pulsed power and its applications, background information is provided for the nonspecialist to better understand the many challenges in designing pulsed power systems, and the wide diversity of applications that are now emerging. The approach to providing a tutorial on pulsed power technology is to make available to the reader the paper written by J. C. Martin which appeared in a Special Section of the Proceedings of the IEEE on pulsed power technology in June 1992. That paper is supplemented in this introduction with additional information that complements many of the invited papers composing this Special Issue.

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+ Quantification of ohmic and intrinsic flux losses in helical flux compression Generators
  Hernandez, J.C.; Neuber, A.A.; Dickens, J.C.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 32, Issue 5, Part 1, Oct. 2004 Page(s):1902 - 1908
Abstract:  Helical magnetic flux compression generators (MFCGs) are the most promising energy sources with respect to their current amplification and compactness. They are able of producing high current pulses required in many pulsed power applications with at least one order of magnitude higher energy density than capacitive storage with similar discharge characteristics. However, the main concern with MFCGs is their intrinsic flux loss that limits severely their performance and which is not yet well understood. In general, all flux losses have a differing degree of impact, depending on the generator's volume, current and energy amplification, size of the driven load, and angular frequency of armature-helix contact point. Although several computer models have been developed in the open literature, none of them truly quantify, starting from basic physics principles, the ohmic and intrinsic flux losses in helical MFCGs. This paper describes a novel method that provides a separate calculation of intrinsic flux losses (flux that is left behind in the conductors and lost for compression) and ohmic losses, being especially easy to implement and fast to calculate. We also provide a second method that uses a simple flux quantification, making a mathematical connection between the intrinsic flux losses, quantified by the first method, and the intrinsic flux losses observed in the generators. This second method can also be used to a priori estimate the MFCG performance. Further, we will show experimental and calculated data and discuss the physical efficiency limits and scaling of generator performance at small sizes.

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+ Research issues in developing compact pulsed power for high peak power applications on mobile platforms
  Gaudet, J.A.; Barker, R.J.; Buchenauer, C.J.; Christodoulou, C.; Dickens, J.; Gundersen, M.A.; Joshi, R.P.; Krompholz, H.G.; Kolb, J.F.; Kuthi, A.; Laroussi, M.; Neuber, A.; Nunnally, W.; Schamiloglu, E.; Schoenbach, K.H.; Tyo, J.S.; Vidmar, R.J.; Proceedings of the IEEE on Pulsed Power, Volume 92, Issue 7, July 2004 Page(s):1144 - 1165
Abstract:  Pulsed power is a technology that is suited to drive electrical loads requiring very large power pulses in short bursts (high-peak power). Certain applications require technology that can be deployed in small spaces under stressful environments, e.g., on a ship, vehicle, or aircraft. In 2001, the U.S. Department of Defense (DoD) launched a long-range (five-year) Multidisciplinary University Research Initiative (MURI) to study fundamental issues for compact pulsed power. This research program is endeavoring to: 1) introduce new materials for use in pulsed power systems; 2) examine alternative topologies for compact pulse generation; 3) study pulsed power switches, including pseudospark switches; and 4) investigate the basic physics related to the generation of pulsed power, such as the behavior of liquid dielectrics under intense electric field conditions. Furthermore, the integration of all of these building blocks is impacted by system architecture (how things are put together). This paper reviews the advances put forth to date by the researchers in this program and will assess the potential impact for future development of compact pulsed power systems

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+ Scanning the Technology
  E. Schamiloglou, R. J. Barker, M. Gunderson, and A. A. Neuber, “Scanning the Technology,” Proceedings of the IEEE, vol. 92, pp. 1014-1020, 2004.
Abstract:  Not Available
+ Unipolar Surface Flashover
  J Krile, A Neuber, H Krompholz, J Dickens, "Unipolar Surface Flashover" APS Meeting Abstracts 1, 1013
Abstract:  Not Available
Publication Year:  2003
+ A Completely Explosive Pulsed Power Mini-System
  "A Completely Explosive Pulsed Power Mini-System", Review of Scientific Instruments, 74, # 1, p 225-230, 2003, (with E.F. Talantsev, S.I. Shkuratov, and J. Dickens).
Abstract:  Not Available
+ Autonomous Ultra-Compact Explosive-Driven High-Voltage Generator Based on a Transverse Shock Wave Demagnetization of Nd2Fe14B Hard Ferromagnetics
  "Autonomous Ultra-Compact Explosive-Driven High-Voltage Generator Based on a Transverse Shock Wave Demagnetization of Nd2Fe14B Hard Ferromagnetics", Review of Scientific Instruments, 74, no. 1, Part 225-230, 2003 (with S.I. Shkuratov, E.F. Talantsev, and J.C. Dickens).
Abstract:  Not Available
+ Currents produced by explosive driven transverse shock wave ferromagnetic source of primary power in a coaxial single-turn seeding coil of a Magnetocumulative generator
  "Currents produced by explosive driven transverse shock wave ferromagnetic source of primary power in a coaxial single-turn seeding coil of a Magnetocumulative generator", Journal of Applied Physics, 93, 4529-4535, 15 April 2003 with Sergey I Shkuratov, Evgueni F. Talantsev and James C. Dickens).
Abstract:  Not Available
+ Efficiency results from a coaxial vircator using a simple feedback technique
  Mankowski, J.; Cheng, X.; Dickens, J.; Kritiansen, M.; Choi, E.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 1, 15-18 June 2003 Page(s):455 - 458 Vol.1
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 /spl sim/9.5%. Measured radiated field patterns show evidence of multimode operation.

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+ Fast, real-time monitoring of rotating machines using digital motion control coprocessors
  M Giesselmann, B McHale, M Crawford, "Fast, real-time monitoring of rotating machines using digital motion control coprocessors" Magnetics, IEEE Transactions on 39 (1), 343-347
Abstract:  Not Available
+ Fast, Real-Time Monitoring of Rotating Machines using Digital Motion Control Co-Processors
  M. Giesselmann, B. McHale, and M. Crawford, “Fast, Real-Time Monitoring of Rotating Machines using Digital Motion Control Co-Processors,” presented at 2002 Electromagnetic Launch Symposium, St. Louis, France, IEEE Transactions on Magnetics, Vol. 39, No.1, January 2003, p. 343-347.
Abstract:  This paper describes the use of methods and techniques that have been developed for high-performance control of relatively small and slow turning industrial machines and extend these techniques to the more demanding regime of AC machines used for kinetic energy storage and fast AC servos for military applications. In particular this paper describes a technique for fast monitoring of the output voltage of AC generators. To accomplish fast monitoring, the (sinusoidal) AC output voltage is converted to a DC quantity that represents the instantaneous amplitude. This is achieved through the use of a rotational transformation. This transformation, also called "vector rotation," can be used for very fast observation of the momentary amplitudes of all electrical machine quantities, such that averaging of the AC value (to determine "momentary average" rms amplitude) is not necessary. The procedure is implemented by tightly integrating a digital motion control coprocessor into the memory map of a 16-bit microcontroller.

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+ Flashover across a dielectric surface at atmospheric pressure
  A Neuber, J Krile, J Dickens, H Krompholz, "Flashover across a dielectric surface at atmospheric pressure" APS Texas Sections Fall Meeting Abstracts 1, 1001
Abstract:  Not Available
+ Helical MFCG For Driving A High Inductance Load
  Andreas A. Neuber, Juan-Carlos Hernández, James C. Dickens, Magne Kristiansen, Electromagnetic Phenomena, vol. 3, pp. 397-404, (2003).
Abstract:  Even at small dimensions of less than 0.5 meter in length end-initiated helical 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. 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 less than 10 kV. Many pulsed power devices require less current but a considerably higher voltage level. For effectively driving a high inductance load of several μH, a multistage MFCG design has been suggested. We successfully tested a dual stage MFCG with a total length of 250 mm, a helix inner diameter of 51 mm, which 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 ~ 13 into a 3 μH load and will discuss the generator performance based on experimental current/voltage waveforms and specify the observed losses.

[PDF]

+ Longitudinal Shock Wave Demagnetization of High Energy Nd2Fe14B Ferromagnetics
  "Longitudinal Shock Wave Demagnetization of High Energy Nd2Fe14B Ferromagnetics", Applied Physics Letters, 82 8, p.1248-1250, 2003, (with S.I. Shkuratov, E.F. Talantsev, and J.C. Dickens).
Abstract:  Not Available
+ Phenomenology of conduction and breakdown in transformer oil
  M Butcher, M Cevallos, M Haustien, A Neuber, J Dickens, H Krompholz, "Phenomenology of conduction and breakdown in transformer oil" Electrical Insulation and Dielectric Phenomena, 2003. Annual Report
Abstract:  Not Available
+ Seed Currents Produced by an Ultracompact Explosive Driven Transverse Shock Wave Ferromagnetic Source of Primary Power in a Seeding Coil of a Magnetocumulative Generator
  "Seed Currents Produced by an Ultracompact Explosive Driven Transverse Shock Wave Ferromagnetic Source of Primary Power in a Seeding Coil of a Magnetocumulative Generator", Applied Physics Letters, 82, 1248-1250, 2003 (with S.I. Shkuratov, E.F. Talantsev, and J.C. Dickens).
Abstract:  Not Available
Publication Year:  2002
+ Compact Explosive-Driven Generator of Primary Power Based on a Longitudinal Shock Wave Demagnetization of Hard Ferri- and Ferromagnetics
  "Compact Explosive-Driven Generator of Primary Power Based on a Longitudinal Shock Wave Demagnetization of Hard Ferri- and Ferromagnetics", IEEE Transactions on Plasma Science Special Issue on Pulsed Power Science and Technology, November 2002, (with S.I. Shkuratov, J.C. Dickens, and J.C. Hernendez).
Abstract:  Not Available
+ Computer Simulation of Power Electronics
  M Giesselmann, "Computer Simulation of Power Electronics" The Power Electronics Handbook, edited by Tim Skvarenina. Chapter 23, p.23-1...23
Abstract:  Not Available
+ Current Mode of Pulsed Power Generation in Moving Magnet Systems
  "Current Mode of Pulsed Power Generation in Moving Magnet Systems", IEEE Transactions on Plasma Science Special Issue on Pulsed Power Science and Technology, November 2002, (with S. Shkuratov, J.C. Dickens, and J.C. Hernandez).
Abstract:  Not Available
+ Extended Kalman Filter Training of Neural Networks on a SIMD Parallel Machine
  Shuhui Li, Donald C. Wunsch, Edgar O’Hair, Michael G. Giesselmann, “Extended Kalman Filter Training of Neural Networks on a SIMD Parallel Machine”, Journal of Parallel and Distributed Computing, Volume 62, Number 4, April 2002, 544-562.
Abstract:  Not Available
+ Extended Kalman filter training of neural networks on a SIMD parallel machine
  S Li, DC Wunsch, E O'Hair, MG Giesselman, "Extended Kalman filter training of neural networks on a SIMD parallel machine" Journal of Parallel and Distributed Computing 62 (4), 544-562
Abstract:  Not Available
+ Field enhanced microwave breakdown in a plasma limiter
  Mankowski, J.J.; Hemmert, D.; Neuber, A.; Krompholz, H.; IEEE Transactions on Plasma Science, Volume 30, Issue 1, Part 1, Feb. 2002 Page(s):102 - 103
Abstract:  A new type of plasma limiter is being developed which can turn on in less than 1 ns. The approach taken is to initiate streamer breakdown via a micron radius needle tip. Images were taken of the gap region in argon at several pressures in order to investigate the role of the tip region

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+ Gas breakdown in the subnanosecond regime with voltages below 15 kV
  Krompholz, H.; Hatfield, L.L.; Kristiansen, M.; Hemmert, D.; Short, B.; Mankowski, J.; Brown, M.D.J.; Altgilbers, L.L.; IEEE Transactions on Plasma Science, Volume 30, Issue 5, Part 1, Oct. 2002 Page(s):1916 - 1921
Abstract:  Gaseous breakdown in the subnanosecond regime is of interest for fast pulsed power switching, short pulse electromagnetics, and for plasma limiters to protect electronic devices from high power microwave radiation. Previous investigations of subnanosecond breakdown were mainly limited to high-pressure gases or liquids, with voltages in excess of 100 kV. In this paper, we investigate subnanosecond breakdown at applied voltages below 7.5 kV in point-plane geometries in argon, with a needle radius <0.5 /spl mu/m. The coaxial setup allows current and voltage measurements with temporal resolutions down to 80 ps. Voltages of 7.5 kV (which are doubled at the open gap before breakdown) produce breakdowns with a delay of about 1 ns. With negative pulses applied to the tip and the same amplitude, breakdown is always observed during the rising part of the pulse, with breakdown delay times below 800 ps, at pressures between 10/sup 2/ and 10/sup 4/ Pa. At lower pressure, a longer delay time (8 ns at 6 Pa) is observed. We expect the breakdown mechanism to be dominated by electron field emission, but still influenced by gaseous amplification.

[PDF]

+ High-speed optical diagnostic of an exploding wire fuse
  M Giesselmann, T Heeren, A Neuber, J Walter, M Kristiansen, "High-speed optical diagnostic of an exploding wire fuse" Plasma Science, IEEE Transactions on 30 (1), 100-101
Abstract:  Not Available
+ High-speed optical diagnostic of an exploding wire fuse
  Giesselmann, M.; Heeren, T.; Neuber, A.; Walter, J.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 30, Issue 1, Part 1, Feb. 2002 Page(s):100 - 101
Abstract:  Explosive flux compression generators generate hundreds of kiloamperes and voltages of a few kilovolts. A power conditioning stage is required since typically voltages in the hundreds of kilovolts range are needed. Inductive energy storage systems with an opening switch provide the necessary voltage gain. In our application, the opening switch has been implemented as an exploding wire fuse. The voltage gain, and hence the performance of the system, is greatly dependent on the opening switch. We utilized high-speed optical imaging (up to 107 pictures/s) to assess the performance of the exploding wire fuse

[PDF]

+ Rapid Capacitor Charger for Compact Marx Generators
  M Giesselmann, T Heeren, "Rapid Capacitor Charger for Compact Marx Generators" SAE Technical Paper, 01-2181
Abstract:  Not Available
+ Shock Wave Demagnetization of BaFe12O19 Hard Ferrimagnetics
  "Shock Wave Demagnetization of BaFe12O19 Hard Ferrimagnetics", Journal of Applied Physics 91 (2002) 3007-3009 (with S.I. Shkuratov, E.F. Talantsev and J. Dickens.
Abstract:  Not Available
+ Single Shot, Repetitive and Life-Time High-Voltage Testing of Capacitors
  "Single Shot, Repetitive and Life-Time High-Voltage Testing of Capacitors", IEEE Transactions on Plasma Science Special Issue on Pulsed Power Science and Technology, 30 1665, October 2002, (with S.I. Shkuratov, E.F. Talantsev, L.L. Hatfield, and J.C. Dickens).
Abstract:  Not Available
+ Subnanosecond corona inception in an ultrawideband environment
  Mankowski, J.; Dickens, J.; Kristiansen, M.; Lehr, J.; Prather, W.; Gaudet, J.; IEEE Transactions on Plasma Science, Volume 30, Issue 3, Part 1, June 2002 Page(s):1211 - 1214
Abstract:  Corona discharges in ultrawideband radiating systems can have adverse effects on performance such as reflection, phase dispersion, and significant power losses. A test-bed has been assembled to experimentally observe corona created by voltage pulses similar to ultrawideband systems. The current work involves the attenuation of an incident pulse after propagation through a self-initiated corona and relative measurements of visible light emission from the photoionization produced during streamer development. Several gas dielectrics, including ambient air, N/sub 2/, H/sub 2/, and SF/sub 6/, were tested.

[PDF]

+ The Conductivity of a Longitudinal-Shock-Wave-Compressed Nd2Fe14B Hard Ferromagnetics
  "The Conductivity of a Longitudinal-Shock-Wave-Compressed Nd2Fe14B Hard Ferromagnetics", Modern Physics Letters B, 16, No. 12 (2002) 1-11 (with E.F. Talantsev, S.I. Shkuratov, and J. Dickens).
Abstract:  Not Available
+ Theoretical Treatment of Explosive Driven Ferroelectric Generators
  "Theoretical Treatment of Explosive Driven Ferroelectric Generators", IEEE Transactions on Plasma Science Special Issue on Pulsed Power Science and Technology, 30 1665, October 2002, (with S.I. Shkuratov, Ya. Tkach, E.F. Talantsev, J. Dickens, L.L. Altgilbers, and P.T. Tracy).
Abstract:  Not Available
+ Thermodynamic state of the magnetic flux compression generator volume
  Neuber, A.; Holt, T.; Dickens, J.C.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 30, Issue 5, Part 1, Oct. 2002 Page(s):1659 - 1664
Abstract:  The thermodynamic state of the gas trapped in the volume of helical magnetic flux compression generators was measured using optical emission spectroscopy and fast pressure probes. Three main stages of operation are discussed: (1) the initial stage, which can be represented by a freely expanding armature, that shows fairly low gas temperatures, as low as 2000 K; (2) the intermediate stage during 14-4 /spl mu/s before generator burnout that exhibits mainly an atomic copper line transition at about 0.8 eV; (3) the last few /spl mu/s that reveal a highly compressed gas with temperatures of about 5000 K and pressures of about 1500 bar. Most experiments were conducted in air, initially at STP, some results are given for argon and sulfur hexafluoride initially at one atmosphere. Additionally, the thermodynamic state is linked to the electrical volume breakdown threshold via simple resistance measurements that were conducted in current-free flux compression generators.

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+ Transverse Shock Wave Demagnetization of Nd2Fe14B High-Energy Hard Ferromagnetics
  "Transverse Shock Wave Demagnetization of Nd2Fe14B High-Energy Hard Ferromagnetics", Journal of Applied Physics 92 (2002) 159-162 (with S.I. Shkuratov, E.F. Talantsev, and J. Dickens).
Abstract:  Not Available
+ Ultracompact Explosive-Driven High-Current Source of Primary Power Badsed on Shock Wave Demagnetization of Nd2Fe14B Hard Ferromagnetics
  "Ultracompact Explosive-Driven High-Current Source of Primary Power Badsed on Shock Wave Demagnetization of Nd2Fe14B Hard Ferromagnetics", Review of Scientific Instruments, 73 (2002) 2738-2742 (with S.I. Shkuratov, E.F. Talantsev, and J. Dickens).
Abstract:  Not Available
+ Vacuum ultraviolet luminous efficiency and plama ion density in alternating current plasma display panels
  "Vacuum ultraviolet luminous efficiency and plama ion density in alternating current plasma display panels", Applied Physics Letters, 81, 3341-3343, 28 October, 2002 (with Eun Ha Choi, Jenon Chulol Ahn, Min Wug Moon, Yoon Jung, Myung Chul Choi, Yoonho Seo, Guangsup Cho, Han Sup Uhm, Kunihide Tachibana, and Ki Woong Whang).
Abstract:  Not Available
Publication Year:  2001
+ 14.1 Power Semiconductor Devices
  K Rajashekara, MM Swamy, M Giesselmann, H Akagi, "14.1 Power Semiconductor Devices" Power Electronics
Abstract:  Not Available
+ Advanced modeling of an exploding flux compression generator using lumped element models of magnetic diffusion
  M Giesselmann, T Heeren, A Neuber, M Kristiansen, "Advanced modeling of an exploding flux compression generator using lumped element models of magnetic diffusion" Pulsed Power Plasma Science, 2001. PPPS-2001. Digest of Technical Papers 1 162-165
Abstract:  Not Available
+ Calculation of air temperature and pressure history during the operation of a flux compression generator
  X Le, J Rasty, A Neuber, J Dickens, M Kristiansen, "Calculation of air temperature and pressure history during the operation of a flux compression generator" Pulsed Power Plasma Science, 2001. PPPS-2001. Digest of Technical Papers 2 (2) 939-942
Abstract:  Not Available
+ Compact design of a 30 kV rapid capacitor charger
  M Giesselmann, M Kristiansen, "Compact design of a 30 kV rapid capacitor charger" Pulsed Power Plasma Science, 2001. PPPS-20001. Digest of Technical Papers 1 640-643
Abstract:  Not Available
+ Comparative Analysis of Regression and Artificial Neural Network models for Wind Turbine Power Curve Estimation
  Shuhui Li, Don C. Wunsch, Edgar O'Hair, and Michael G. Giesselmann, "Comparative Analysis of Regression and Artificial Neural Network models for Wind Turbine Power Curve Estimation", Transactions of the ASME, Journal of Solar Energy Engineering, Vol. 123, November 2001.
Abstract:  Not Available
+ Comparative analysis of regression and artificial neural network models for wind turbine power curve estimation
  S Li, DC Wunsch, E O'Hair, MG Giesselmann, "Comparative analysis of regression and artificial neural network models for wind turbine power curve estimation" Journal of Solar Energy Engineering 123,327
Abstract:  Not Available
+ Electrical behavior of a simple helical flux compression generator for code benchmarking
  Neuber, A.; Dickens, J.; Cornette, J.B.; Jamison, K.; Parkinson, E.R.; Giesselmann, M.; Worsey, P.; Baird, J.; Schmidt, M.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 29, Issue 4, Aug. 2001 Page(s):573 - 581
Abstract:  A variety of basic magnetic flux compression (MFC) generator geometries have been tested during the last three decades. Though size and operating regimes differ widely, 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 is solely based on physical principles and manages without heuristic factors. A simple generator was designed to address flux and current losses of the helical generator. The generator's maximum current amplitude is given as a function of the seed current and the resulting “seed-current” spread is compared to the output of state-of-the-art computer models. Temporally resolved current and current time derivative signals are compared as well. The detailed generator geometry is introduced in order to facilitate future computer code bench marking or development. The impact of this research on the present understanding of magnetic flux losses in helical MFC generators is briefly discussed

[PDF]

+ High speed optical diagnostics of an exploding wire fuse for power conditioning of explosive flux compression generators
  M Giesselmann, T Heeren, A Neuber, J Walter, M Kristiansen, "High speed optical diagnostics of an exploding wire fuse for power conditioning of explosive flux compression generators" Pulsed Power Plasma Science, 2001. PPPS-2001. Digest of Technical Papers 1 (1) 102-105
Abstract:  Not Available
+ Modeling of a Compulsator and Railgun System
  Michael Giesselmann and Don Eccleshall, “Modeling of a Compulsator and Railgun System”, IEEE Transactions on Magnetics, Vol. 37, No.1, January 2001, p. 129…134.
Abstract:  Not Available
+ Modeling of a compulsator and railgun system
  M Giesselmann, D Eccleshall, "Modeling of a compulsator and railgun system" Magnetics, IEEE Transactions on 37 (1), 129-134
Abstract:  Not Available
+ Pulsed Power Systems
  "Pulsed Power Systems"”, Encyclopedia of Physical Science and Technology, Third Edition edited by Robert A. Meyers, Vol. 13 (2001), Academic Press, Inc., San Diego, CA (with James C. Dickens).
Abstract:  Not Available
+ Studies on a Helical Magnetic Flux Compression Generator
  A. Neuber, J. Dickens, M. Giesselmann, M. Kristiansen, B. Freeman, D. Dorsey, P. Worsey, J. Baird, M. Schmidt, “Studies on a Helical Magnetic Flux Compression Generator”, Paper 2000-01-3617, Journal of Aerospace, SAE 2000 Transactions, Section 1, ISBN 0-7680-0840-9, © 2001, p. 865…869.
Abstract:  Not Available
+ Theory of the virtual cathode oscillator
  "Theory of the virtual cathode oscillator", Physics of Plasmas, 8, #8, Aug 2001 (with Weihua Jiang).
Abstract:  Not Available
+ Using Neural Networks to Estimate Wind Turbine Power Generation
  Shuhui Li, Donald C. Wunsch II, Edgar O'Hair, and Michael G. Giesselmann, “Using Neural Networks to Estimate Wind Turbine Power Generation”, IEEE Transactions on Energy Production, No. 3, Vol. 16, September 2001.
Abstract:  Not Available
Publication Year:  2000
+ A review of short pulse generator technology
  Mankowski, J.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 28, Issue 1, Feb. 2000 Page(s):102 - 108
Abstract:  Today's ultrafast, pulse generators are capable of producing high-voltage pulses, (>1 kV), with fast, leading-edge rise times, (<1 ns). A review of generator implementation methods is presented that includes a detailed discussion of the various circuit designs and a list of commercially available high-voltage pulse generators. All of these generators are capable of rise times less than a few ns and voltages greater than several hundred volts. Finally, a brief description of the three primary switch types, reed, spark gap, and solid state is presented

[PDF]

+ Dielectric/Gas Interface Breakdown Caused by High Power Microwaves
  D. Hemmert, A. Neuber, H. Krompholz, L.L Hatfield, and M. Kristiansen: Dielectric/Gas Interface Breakdown Caused by High Power Microwaves. Proceedings of the 13th International Conference on High-Power Particle Beams, June 25-30, 2000, Nagaoka, Japan, invited.
Abstract:  Not Available
+ Experimental and analytical investigation of a pulsed power conditioning system for magnetic flux compression generators
  M Giesselmann, T Heeren, E Kristiansen, JG Kim, JC Dickens, M Kristiansen, "Experimental and analytical investigation of a pulsed power conditioning system for magnetic flux compression generators" Plasma Science, IEEE Transactions on 28 (5), 1368-1376
Abstract:  Not Available
+ Experimental and Analytical Investigation of a Pulsed Power Conditioning System for Magnetic Flux Compression Generators
  M. Giesselmann, T. Heeren, E. Kristiansen, J. Kim, J. Dickens, M. Kristiansen, “Experimental and Analytical Investigation of a Pulsed Power Conditioning System for Magnetic Flux Compression Generators”, IEEE Transactions on Plasma Science, October 2000, p. 1368…1376.
Abstract:  Not Available
+ High Current and High Voltage Pulsed Testing of Resistors
  "High Current and High Voltage Pulsed Testing of Resistors", IEEE Transactions on Plasma Science, Special Issue on Pulsed Power Science and Technology, 28 1607-1614, Oct. 2000 (with S.I. Shkuratov, J. Dickens, L.L. Hatfield, and E. Horrocks).
Abstract:  Not Available
+ High-power microwave window breakdown under vacuum and atmospheric conditions
  D Hemmert, AA Neuber, JC Dickens, H Krompholz, LL Hatfield, M Kristiansen, "High-power microwave window breakdown under vacuum and atmospheric conditions" Proceedings of SPIE 4031, 90
Abstract:  Not Available
+ Microwave magnetic field effects on high-power microwave window breakdown
  Hemmert, D.; Neuber, A.A.; Dickens, J.; Krompholz, H.; Hatfield, L.L.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 28, Issue 3, June 2000 Page(s):472 - 477
Abstract:  Microwave window breakdown in vacuum is investigated for an idealized geometry, where a dielectric slab is located in the center of a rectangular waveguide with its normal parallel to the microwave direction of propagation. An S-band resonant ring with a frequency of 2.85 GHz and a power of 60 MW is used. With field enhancement tips at the edges of the dielectric slab, the threshold power for breakdown is observed to be dependent on the direction of the microwaves; i.e., it is approximately 20% higher for the downstream side of the slab than it is for the upstream side. Simple trajectory calculations of secondary electrons in an RF field show a significant forward motion of electrons parallel to the direction of microwave propagation. Electrons participating in a saturated secondary avalanche on the upstream side are driven into the surface, and electrons on the downstream side are driven off the surface, because of the influence of the microwave magnetic field. In agreement with the standard model of dielectric surface flashover for dc conditions (saturated avalanche and electron-induced outgassing), the corresponding change in the surface charge density is expected to be proportional to the applied breakdown threshold electric field parallel to the surface

[PDF]

+ Optical diagnostics on helical flux compression generators
  Neuber, A.A.; Dickens, J.C.; Krompholz, H.; Schmidt, M.F.C.; Baird, J.; Worsey, P.N.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 28, Issue 5, Oct. 2000 Page(s):1445 - 1450
Abstract:  Explosively driven magnetic flux compression (MFC) has been object of research for more than three decades. Actual interest in the basic physical picture of flux compression has been heightened by a newly started Department of Defense (DoD) Multi-University Research Initiative. The emphasis is on helical flux compression generators comprising a hollow cylindrical metal liner filled with high explosives and at least one helical coil surrounding the liner. After the application of a seed current, magnetic flux is trapped and high current is generated by moving, i.e., expanding, the liner explosively along the winding of the helical coil. Several key factors involved in the temporal development can be addresses by optical diagnostics. 1) The uniformity of liner expansion is captured by framing camera photography and supplemented by laser illuminated high spatial and temporal resolution imaging. Also, X-ray flash photography is insensitive to possible image blur by shockwaves coming from the exploding liner. 2) The thermodynamic state of the shocked gas is assessed by spatially and temporally resolved emission spectroscopy. 3) The moving liner-coil contact point is a possible source of high electric losses and is preferentially monitored also by emission spectroscopy. Since optical access to the region between liner and coil is not always guaranteed, optical fibers can he used to extract light from the generator. The information so gained will give, together with detailed electrical diagnostics, more insight in the physical loss mechanisms involved in MFC

[PDF]

+ Pulsed Power Generation Using Ferromagnetic Circuits
  "Pulsed Power Generation Using Ferromagnetic Circuits", IEEE Transactions on Plasma Science, Special Issue on Pulsed Power Science and Technology, 28 1347-1352, Oct. 2000 (with S.I. Shkuratov, J. Dickens, L.L. Hatfield, and R. Martin).
Abstract:  Not Available
+ Studies on a helical magnetic flux compression generator
  A Neuber, J Dickens, M Giesselmann, M Kristiansen, B Freeman, D Dorsey, P Worsey, J Baird, M Schmidt, "Studies on a helical magnetic flux compression generator" SAE Transactions 109 (1), 865-869
Abstract:  Not Available
+ The role of outgassing in surface flashover under vacuum
  Neuber, A.A.; Butcher, M.; Krompholz, H.; Hatfield, L.L.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 28, Issue 5, Oct. 2000 Page(s):1593 - 1598
Abstract:  Results of high-speed electrical and optical diagnostics are used as a basis to discuss a new surface flashover model. Outgassing, caused by electron stimulated desorption, is found to play a crucial role in the temporal flashover development. Dielectric unipolar surface flashover under vacuum is experimentally characterized by a three-phase development, which covers a current range from 10-4 A to 100 A. Phase one comprises a fast (several nanoseconds) buildup of a saturated secondary electron avalanche reaching current levels of 10 to 100 mA. Phase two is associated with a slow current amplification reaching currents in the Ampere level within typically 100 ns. The final phase is characterized by a fast current rise up to the impedance-limited current on the order of 100 A. The development during phase two and three is described by a zero-dimensional model, where electron-induced outgassing leads to a Townsend-like gas discharge above the surface. This is supported by time-resolved spectroscopy that reveals the existence of excited atomic hydrogen and ionic carbon before the final phase. The feedback mechanism toward a self-sustained discharge is due to space charge leading to an enhanced field emission from the cathode. A priori unknown model parameters, such as outgassing rate and gas density buildup above the surface, are determined by fitting calculated results to experimental data. The significance of outgassing is also discussed with a view to microwave surface flashover

[PDF]

Publication Year:  1999
+ Dielectric surface flashover in vacuum at 100 K
  Neuber, A.; Butcher, M.; Hatfield, L.L.; Kristiansen, M.; Krompholz, H.; IEEE Transactions on Dielectrics and Electrical Insulation, [see also IEEE Transactions on Electrical Insulation], Volume 6, Issue 4, Aug. 1999 Page(s):512 - 515
Abstract:  Cryogenic components in high power electrical systems and in power electronics gain more and more importance. The behavior of insulators for cryogenic conditions, however, is virtually unknown. In a fast coaxial setup, dielectric test sample and electrodes in vacuum are cooled to <100 K and flashover is characterized using fast electrical and optical diagnostics. Three consecutive development stages for flashover in self-breakdown mode with a gap distance of 0.5 cm can be distinguished: (1) a fast current rise to mA amplitudes within ~2 ns, probably associated with field emission, followed by, (2) a slow current rise to ~5 to 10 A amplitude with duration of 40 ns to 1 μs, associated with secondary emission avalanche saturation, and (3) a transition to a rapid gaseous ionization above the sample caused by electron induced outgassing, leading to impedance-limited current amplitudes of ⩽300 A. Phase (1) shows a higher final current at lower temperature, which is probably due to a higher initial velocity of the secondary electrons, the duration of phase (2) is a decreasing function of breakdown voltage and only slightly dependent on temperature, which points to a weak temperature dependence of the outgassing process. Flashover potentials show a slight increase at lower temperature

[PDF]

+ Dielectric surface flashover in vacuum at 100 K
  A Neuber, M Butcher, LL Hatfield, M Kristiansen, H Krompholz, "Dielectric surface flashover in vacuum at 100 K" Dielectrics and Electrical Insulation, IEEE Transactions on 6 (4), 512-515
Abstract:  Not Available
+ Efficiency Enhancement of Coaxial Virtual Cathode Oscillator
  "Efficiency Enhancement of Coaxial Virtual Cathode Oscillator", 27 1543 (1999) IEEE Transaction Plasma Science, (with W. Jiang and J. Dickens).
Abstract:  Not Available
+ Electric Current in DC Surface Flashover in Vacuum
  A. Neuber, M. Butcher, L. L. Hatfield, and H. Krompholz: Electric Current in DC Surface Flashover in Vacuum. J. Appl. Phys., vol. 15, 3084-3091 (1999)
Abstract:  Not Available
+ Electric current in dc surface flashover in vacuum
  A Neuber, M Butcher, LL Hatfield, H Krompholz, "Electric current in dc surface flashover in vacuum" Journal of applied physics 85, 3084
Abstract:  Not Available
+ High Power Microwave Generation by a Coaxial Virtual Cathode Oscillator
  "High Power Microwave Generation by a Coaxial Virtual Cathode Oscillator", IEEE Transactions on Plasma Science, 27 1538 (1999) (with W. Jiang, K. Woolverton, and J. Dickens).
Abstract:  Not Available
+ Imaging of high-power microwave-induced surface flashover
  Neuber, A.; Hemmert, D.; Dickens, J.; Krompholz, H.; Hatfield, L.L.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 27, Issue 1, Feb. 1999 Page(s):138 - 139
Abstract:  Using two gated intensified digital charge-coupled device cameras, one sensitive in the near infrared to ultraviolet region and one in the soft X-ray region, the temporal development of high-power microwave-induced surface flashover across a vacuum/dielectric interface has been imaged. The emission of X-ray radiation from the interface is caused by field emitted electrons accelerated in the high electromagnetic field impacting the solid. This generation of bremsstrahlung terminates at the moment of full flashover development that is indicated by the optical light emission. A rising plasma density above the dielectric surface due to electron induced outgassing triggers this behavior

[PDF]

+ Initiation of High Power Microwave Dielectric Interface Breakdown
  A. Neuber, D. Hemmert, H. Krompholz, L. Hatfield, and M. Kristiansen: Initiation of High Power Microwave Dielectric Interface Breakdown. J. Appl. Phys., vol. 86, 1724-1728 (1999).
Abstract:  Not Available
+ MULTI-STREAM EXTENDED KALMAN FILTER TRAINING OF NEURAL NETWORKS ON A SIMD PARALLEL MACHINE
  S Li, E O'Hair, DC Wunsch, MG Giesselmann, "MULTI-STREAM EXTENDED KALMAN FILTER TRAINING OF NEURAL NETWORKS ON A SIMD PARALLEL MACHINE" Smart engineering system design: neural networks, fuzzy logic, evolutionary programming, data mining and complex systems: proceedings of the Artificial Neural Networks in Engineering Conference (ANNIE'99), held November 7-10, 1999, in St. Louis, Missouri, USA
Abstract:  Not Available
+ Using PSpice 8.0 to Teach Digital Logic
  M. G. Giesselmann, “Using PSpice 8.0 to Teach Digital Logic”, IEEE Transactions on Education, Vol. 24, No. 4., Nov. 1999, p. 356 and CD-ROM supplement.
Abstract:  Not Available
Publication Year:  1998
+ Finite Rate Chemistry and NO Molefraction in Non-Premixed Turbulent Flames
  A. Neuber, G. Krieger, M. Tacke, E. Hassel, and J. Janicka: Combustion and Flame, vol. 113, 198-211 (1998)
Abstract:  Finite rate chemistry is investigated in turbulent N2-diluted H2 diffusion flames by means of laser spectroscopic methods and a numerical model of combustion. The major species occurring in these hydrogen flames or the temperature are measured with SRS (Spontaneous Raman Spectroscopy) or Rayleigh spectroscopy. Some minor species, the radical OH and the pollutant NO, are simultaneously measured with linear LIF (Laser Induced Fluorescence). Multidimensional pdfs (probability density function) can be deduced from these measurements. Use is made of a numerical model with two principal variables, mixture fraction ξ and reaction progress variable η, as a basis for discussion of the experimental results. A k-ε-turbulence model together with a two-dimensional presumed pdf for the coupling of turbulence and chemistry are applied. So, experimental two-dimensional pdfs as well as mean values of ξ and η as functions of the position in the flame are deduced from the simultaneous measurements. The experimental and theoretical spatial maxima of the mean OH molefraction agree well in magnitude, despite the correlation coefficient between ξ and η of the measured pdf can be as high as 0.5. The neglect of this covariance for the calculation of the presumed pdf is quantified. It results in clear deviations for the OH molefraction. The experimental NO and OH molefractions are better simulated by flame calculations carried out with the presented combustion model than by the also shown calculations based on a single variable for description of chemistry.

[PDF]

+ High voltage subnanosecond breakdown
  Mankowski, J.; Dickens, J.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 26, Issue 3, June 1998 Page(s):874 - 881
Abstract:  Present-day ultra-wideband radiation sources produce Megavolt pulses at hundreds of picosecond (ps) risetimes. Empirical data on the breakdown characteristics for dielectric media at these short time lengths and high voltages are either extremely limited or nonexistent. In support of the design of these ultra-wideband sources, we are investigating the breakdown characteristics, at these voltages and time lengths, of several liquids and high-pressure gases. These include air, N2, H2, SF6, and transformer oil. Gap voltages attained were over 700 kV and gas pressures were over 150 atm (15 MPa). Breakdown times achieved were on the order of 600 ps. Electric field strengths observed for given breakdown times were higher than predicted by other investigators. An empirical fit is presented for the data obtained

[PDF]

+ Window breakdown caused by high-power microwaves
  Neuber, A.; Dickens, J.; Hemmert, D.; Krompholz, H.; Hatfield, L.L.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 26, Issue 3, June 1998 Page(s):296 -
Abstract:  Physical mechanisms leading to microwave breakdown on windows 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 10-6 Pa, 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. Diagnostics include the measurement of incident/reflected power, measurement of local microwave fields, discharge luminosity, and X-ray emission. All quantities are recorded with 0.21-ns resolution. In addition, a framing camera with gating times of 5 ns is used. The breakdown processes for the case with a purely tangential electric field is similar to DC flashover across insulators, and similar methods to increase the flashover field are expected to be applicable

[PDF]

Publication Year:  1997
+ Arc Erosion Behavior of Cu-15% Nb and Cu-15% Cr in Situ Composites”, Elsevier
  "Arc Erosion Behavior of Cu-15% Nb and Cu-15% Cr in Situ Composites”, Elsevier", Wear: an International Journal on Science and Technology of Friction and Wear” 36 (1997) (with P. Liu, S. Bahadur (Univ. Of Iowa) and Anthony L. Donaldson).
Abstract:  Not Available
+ Dielectric Surface Flashover in a Simulated Low Earth Orbit Environment
  F. Hegeler, H. Krompholz, L.L. Hatfield, M. Kristiansen, “Dielectric Surface Flashover in a Simulated Low Earth Orbit Environment”, IEEE Transactions on Plasma Science, 25 (1997) 300
Abstract:  Not Available
+ Dynamic models of 3-phase alternators including saliency effects using Pspice for Windows
  M Giesselmann, "Dynamic models of 3-phase alternators including saliency effects using PSpice for Windows" Magnetics, IEEE Transactions on 33 (1), 231-236
Abstract:  Not Available
+ Dynamic Models of 3-Phase Alternators Including Saliency Effects using PSpice for Windows
  M. Giesselmann, "Dynamic Models of 3-Phase Alternators Including Saliency Effects using PSpice for Windows”, IEEE Transactions on Magnetics, Vol. 33, Number 1, Jan. 1997, p. 231-236.
Abstract:  Not Available
+ Electrical and Optical Characterization of Crystalline Silicon/Porous Silicon Hetero-junctions
  "Electrical and Optical Characterization of Crystalline Silicon/Porous Silicon Hetero-junctions", Solar Energy Materials and Solar Cells, 46, 261 (1997) (with C. Palsule, S. Liu, S. Gangopadhyay, M. Holtz, and D. Lamp).
Abstract:  Not Available
+ Simulation of Fuzzy Logic Control with MicroSim's PSpice 8.0
  M. Giesselmann, "Simulation of Fuzzy Logic Control with MicroSim's PSpice 8.0", MicroSim Source Magazine, December 1997, p. 3-8.
Abstract:  Not Available
+ Using neural networks to predict wind power generation
  S Li, E O'Hair, MG Giesselmann, "Using neural networks to predict wind power generation" Solar Engineering, 415-420
Abstract:  Not Available
Publication Year:  1995
+ Review of the Mechanisms of Electrode and Insulator Erosion and Degradation in High Current Arc Environments
  "Review of the Mechanisms of Electrode and Insulator Erosion and Degradation in High Current Arc Environments", IEEE Transactions on Magnetics, 31, 709, (1995) (with T.G. Engel, S.L. Wester, and A.L. Donaldson).
Abstract:  Not Available
Publication Year:  1994
+ Electron-Beam Controlled Switching Using Quartz and Polycrystalline ZnSe
  "Electron-Beam Controlled Switching Using Quartz and Polycrystalline ZnSe", IEEE Transactions on Electron Devices, 41, 582 (1994) (with W. Jiang, K. Zinsmeyer, M. Less, and K.H. Schoenbach).
Abstract:  Not Available
+ Plasma Development in the Early Phase of Dielectric Surface Flashover
  G. Masten, T. Mueller, F. Hegeler, H. Krompholz, "Plasma Development in the Early Phase of Dielectric Surface Flashover", IEEE Transactions on Plasma Science, 22 (1994) 1034
Abstract:  Not Available
Publication Year:  1993
+ Current, Luminosity, and X-ray Emission in the Early Phase of Dielectric Surface Flashover in Vacuum
  F. Hegeler, G. Masten, H. Krompholz, and L.L Hatfield, "Current, Luminosity, and X-ray Emission in the Early Phase of Dielectric Surface Flashover in Vacuum", IEEE Transactions on Plasma Science, 21 (1993) 223
Abstract:  Not Available
+ Insulator and Electrode Mass Erosion and Surface Voltage Holdoff Recovery for Transient, High Current Surface Discharges
  "Insulator and Electrode Mass Erosion and Surface Voltage Holdoff Recovery for Transient, High Current Surface Discharges", IEEE Transactions on Magnetics, 29, 1143 (1993) (with T.G. Engel and J.C. Dickens).
Abstract:  Not Available
Publication Year:  1992
+ Magnetic field effects on vacuum insulator flashover
  M. Lehr, R. Korzekwa, H. Krompholz, M. Kristiansen, "Magnetic field effects on vacuum insulator flashover", J. Appl. Phys. 71 (1992) 389
Abstract:  Not Available
Publication Year:  1991
+ Estimating the Erosion and Degradation Performance of Ceramic and Polymeric Insulator Materials in High Current Arc Environments
  "Estimating the Erosion and Degradation Performance of Ceramic and Polymeric Insulator Materials in High Current Arc Environments", IEEE Transactions on Magnetics, 27, 533, (1991) (with T.G. Engel, E. O'Hair, and J.N. Marx).
Abstract:  Not Available
+ Expansion of Hydrogen Arcs Driven by Oscillating Currents
  T.G. Engel, M. Kristiansen, H. Krompholz, "Expansion of Hydrogen Arcs Driven by Oscillating Currents", IEEE Transactions on Plasma Science 19 (1991) 959
Abstract:  Not Available
+ Picosecond Time-Resolved Photoluminescence Characterization of a-SiC:H Films Prepared by Electron Cyclotron Resonance Plasma
  "Picosecond Time-Resolved Photoluminescence Characterization of a-SiC:H Films Prepared by Electron Cyclotron Resonance Plasma", J. Non-Cryst. Solids, 137 and 138, 859 (1991) (with S. Gangopadhyay, M. Pleil, W. Borst, and C. Young).
Abstract:  Not Available
+ Plasma Diagnostics for High Power Ignitron Development
  D.L. Loree, M. Giesselmann, M. Kristiansen and A. Shulski, "Plasma Diagnostics for High Power Ignitron Development", IEEE Transactions on Magnetics, Vol. 27, No.1, January 1991.
Abstract:  Not Available
+ Surface-Discharge Switch Design: The Critical Factor
  "Surface-Discharge Switch Design: The Critical Factor", IEEE Trans. Electron Devices, 38, 740, (1991) (with T.G. Engel, M.C. Baker, and L.L. Hatfield).
Abstract:  Not Available
+ The Design and Calibration of a Very Fast Current Probe for Short Pulse Measurements
  S. Calico, M. Crawford, M. Kristiansen, H. Krompholz, "The Design and Calibration of a Very Fast Current Probe for Short Pulse Measurements", Rev. Sci. Instrum 62 (1991) 1511
Abstract:  Not Available
Publication Year:  1990
+ On the Road to Tomsk
  "On the Road to Tomsk", Physics Today, June 1990, 36 (with A.H. Guenther and J.E. Thompson) also translated to Japanese, Physical Science Magazine, Dec. 1990.
Abstract:  Not Available
+ The Influence of Magnetic Fields on Dielectric Surface Flashover
  R. Korzekwa, M. Lehr, H. Krompholz, M. Kristiansen, "The Influence of Magnetic Fields on Dielectric Surface Flashover", IEEE Transactions on Electron Devices, 38 (1990) 745
Abstract:  Not Available
+ Voltage-Current Characteristics of a High-Current Pulsed Discharge in SF6
  "Voltage-Current Characteristics of a High-Current Pulsed Discharge in SF6", (in Japanese), Denki Gakkai Ronbunshi, 110-B, No. 7, 560, (1990)(with Hidenori Akiyama, Tetsuro Tanigawa, Sadao Maeda, and Koichi Takaki), also translated to English in Scripta Technica. (See #102.)
Abstract:  Not Available
+ Voltage-Current Characteristics of High-Current Pulsed Discharges in SF6, Electrical Engineering in Japan
  "Voltage-Current Characteristics of High-Current Pulsed Discharges in SF6, Electrical Engineering in Japan", 111, No. 3 July 1991 (translated from Denki Gakkai Ronbunshi, 110B, No. 7, July 1990, 560-567 (with Hidenori Akiyama, Tetsuro Tanigawa, Sadao Maeda and Koichi Takaki). (Also see #92.)
Abstract:  Not Available
Publication Year:  1989
+ Design Options for Optically Restructuring Damaged Image Detectors
  "Design Options for Optically Restructuring Damaged Image Detectors", SPIE/ Optical Engineering, 28, 854 (1989) (with E.A. Igel).
Abstract:  Not Available
+ Electrode Erosion from High Current Moving Arcs
  "Electrode Erosion from High Current Moving Arcs", IEEE Trans. on Plasms Science, PS-17, 811 (1989) (with F. Mark Lehr).
Abstract:  Not Available
+ Inhibiting Surface Flashover for Space Conditions Using Magnetic Fields
  R. Korzekwa, M. Lehr, H. Krompholz, M. Kristiansen, "Inhibiting Surface Flashover for Space Conditions Using Magnetic Fields", IEEE Trans. on Plasma Science, 17 (1989) 612
Abstract:  Not Available
+ Methods of Increasing the Surface Flashover Potential in Vacuum
  L.L. Hatfield, E.R. Boerwinkle, G. Leiker, H. Krompholz, R. Korzekwa, M. Lehr, M. Kristiansen, "Methods of Increasing the Surface Flashover Potential in Vacuum", IEEE Trans. on Electrical Insulation, 24 (1989) 985
Abstract:  Not Available
+ State-of-the-Art Insulator and Electrode Materials for Use in High Current, High Energy Switching
  "State-of-the-Art Insulator and Electrode Materials for Use in High Current, High Energy Switching", IEEE Trans. on Magnetics, MAG-25, 138 (1989) (with A.L. Donaldson and T.G. Engel).
Abstract:  Not Available
+ The Performance of New, Redesigned Ignitron Tubes in Axial Magnetic Fields
  D. Adkins, M. Giesselmann, and M. Kristiansen, "The Performance of New, Redesigned Ignitron Tubes in Axial Magnetic Fields", IEEE Transactions on Magnetics, Vol. 25, No. 1, January 1989, p. 27...32.
Abstract:  Not Available
+ The Pulsed Discharge Arc Resistance and Its Functional Behavior
  "The Pulsed Discharge Arc Resistance and Its Functional Behavior", IEEE Trans. on Plasma Science, PS-17, 323 (1989) (with T.G. Engel and A.L. Donaldson).
Abstract:  Not Available
+ Warm Plasma Dispersion Relation of the Fast Alfven Wave for Asymmetrical Heating Current Drive
  "Warm Plasma Dispersion Relation of the Fast Alfven Wave for Asymmetrical Heating Current Drive", IEEE Trans. Plasma Science, PS-17, 520 (1989) (with J. Gahl, O. Ishihara, and M. Hagler).
Abstract:  Not Available
Publication Year:  1988
+ Analytical and Experimental Investigations of Reed Contact Bouncing
  "Analytical and Experimental Investigations of Reed Contact Bouncing", IEEE Trans. on Components, Hybrids, and Manufacturing Technology" CHMT-11, 200 (1988) (with B. Miedzinski).
Abstract:  Not Available
+ CO2-Laser Enhanced Electron Attachment in Externally Sustained Diffuse Gas Discharges Containing Vinyl Chloride
  G. Schaefer, M. Giesselmann, B. Pashaie, and M. Kristiansen, "CO2-Laser Enhanced Electron Attachment in Externally Sustained Diffuse Gas Discharges Containing Vinyl Chloride", Journal of Applied Physics 64 (11), 1 December 1988, p. 6123...6127.
Abstract:  Not Available
+ Current-Voltage Characteristics of a High Current Pulsed Discharge in Air
  H. Akiyama, M. Kristiansen, H. Krompholz, B. Maas, "Current-Voltage Characteristics of a High Current Pulsed Discharge in Air", IEEE Trans. on Plasma Science 16 (1988) 312
Abstract:  Not Available
+ Optimization of Gas Mixtures for Electron Beam Controlled Diffuse Discharge Opening Switches
  "Optimization of Gas Mixtures for Electron Beam Controlled Diffuse Discharge Opening Switches", J. Appl. Phys., 63, 1372 (1988) (with R. Korzekwa and G. Schaefer).
Abstract:  Not Available
Publication Year:  1987
+ Fast Alfven Wave Propagation in a Deuterium-Hydrogen Tokamak Plasma
  "Fast Alfven Wave Propagation in a Deuterium-Hydrogen Tokamak Plasma," Plasma Phys. and Controlled Fusion, 29, 93 (1987) (with H. Akiyama, K.L. Wong, J. Gahl and M. Hagler).
Abstract:  Not Available
+ Numerical Studies of Minority Ion Heating Current Drive
  "Numerical Studies of Minority Ion Heating Current Drive," Phys. Fluids, 30, 834 (1987) (with K.L. Wong, O. Ishihara, J. Gahl and M. Hagler).
Abstract:  Not Available
+ Observation of Local Cavity Resonances of Fast Alfven Waves
  "Observation of Local Cavity Resonances of Fast Alfven Waves," Nuclear Fusion, 27, 151 (1987)(with K.L. Wong, M. Hagler, O. Ishihara and H. Akiyama).
Abstract:  Not Available
+ Pulsed Power Systems": Encyclopedia of Physical Science and Technology
  "Pulsed Power Systems": Encyclopedia of Physical Science and Technology, 11, 410 (1987), Academic Press, Inc., San Diego, CA (with M.O. Hagler).
Abstract:  Not Available
Publication Year:  1986
+ Analytical Studies of an Ablation Mass Driver System
  "Analytical Studies of an Ablation Mass Driver System," J. Appl. Phys., 59, 3397 (1986) (with K. Ikuta and M.F. Rose).
Abstract:  Not Available
+ Charging of Insulators in a Surface Discharge Switch
  "Charging of Insulators in a Surface Discharge Switch," IEEE Trans. Elec. Insulation EI-21, 145 (1986) (with R.D. Curry, V.K. Agarwal, L.L. Hatfield and G.R. Leiker).
Abstract:  Not Available
+ Conical Linear Implosion as a Projectile Injector for Mass Drivers
  "Conical Linear Implosion as a Projectile Injector for Mass Drivers," Japanese J. Appl. Phys. 25, L198 (1986) (with K. Ikuta).
Abstract:  Not Available
+ Electrode Erosion in High Current, High Energy Transient Arcs
  "Electrode Erosion in High Current, High Energy Transient Arcs," IEEE Trans. Mag., MAG-22, 1441 (1986) (with A.L. Donaldson, A. Watson, K. Zinsmeyer, E. Kristiansen, and Rolf Dethlefsen).
Abstract:  Not Available
+ Experimental Observation of Current Generation by Asymmetrical Heating of Ions in a Tokamak Plasma
  "Experimental Observation of Current Generation by Asymmetrical Heating of Ions in a Tokamak Plasma," J. Appl. Physics 60, 4322 (1986) (with J. Gahl, O. Ishihara, K.L. Wong and M. Hagler).
Abstract:  Not Available
+ Insulator Damage in High Current Discharges
  "Insulator Damage in High Current Discharges," IEEE Trans. Mag., MAG-22, 1695 (1986) (with P.M. Ranon, F.M. Lehr and L.L. Hatfield).
Abstract:  Not Available
+ Kurzzeitoptische Untersuchungen der Entladungsentwicklung in N2 und SF6 an Modellanordnungen bei Gleich- und Impulsspannung
  Michael Giesselmann, "Kurzzeitoptische Untersuchungen der Entladungsentwicklung in N2 und SF6 an Modellanordnungen bei Gleich- und Impulsspannung" (Short Time Optical Investigations of the Discharge Development in N2 and SF6 at Model Arrangements under DC- and Impulse Voltage Stress), Ph.D. Dissertation, August 1986 (in German).
Abstract:  Not Available
+ Mechanism of Electrode Surface Damage and Material Removal in High Current Discharges
  "Mechanism of Electrode Surface Damage and Material Removal in High Current Discharges," IEEE Trans. Mag., MAG-22, 1799 (1986) (with A. Watson, A.L. Donaldson and K. Ikuta).
Abstract:  Not Available
+ Reliability Assurance in Electromagnetic Launch Technology
  "Reliability Assurance in Electromagnetic Launch Technology," IEEE Trans. Mag., MAG-22, 1567 (1986) (with W.J. Kolarik and T.L. Landers).
Abstract:  Not Available
+ The Influence of the Circuit Impedance on an Electron-Beam Controlled Diffuse Discharge with a Negative Differential Conductivity
  "The Influence of the Circuit Impedance on an Electron-Beam Controlled Diffuse Discharge with a Negative Differential Conductivity," Appl. Phys. Lett. 48, 1776 (1986) (with G. Schaefer, K.H. Schoenbach, B.E. Strickland, R.A. Korzekwa and G.Z. Hutcheson).
Abstract:  Not Available
Publication Year:  1985
+ A New Design Concept for Field Distortion Trigger Spark Gaps
  . Schaefer, B. Pashaie, P. Williams, K. Schoenbach, H. Krompholz, "A New Design Concept for Field Distortion Trigger Spark Gaps", J. Appl. Phys. 57 (1985) 2507
Abstract:  Not Available
+ An Electron Beam Controlled Diffuse Discharge Switch
  K. Schoenbach, G. Schaefer, M. Kristiansen, H. Krompholz, H. Harjes, D. Skaggs, "An Electron Beam Controlled Diffuse Discharge Switch", J. Appl. Phys. 57 (1985) 1618
Abstract:  Not Available
+ Antenna for Unidirectional Propagation of Fast Alfven Waves in a Tokamak
  "Antenna for Unidirectional Propagation of Fast Alfven Waves in a Tokamak," Rev. Sci. Instrum. 56, 1151 (1985) (with H. Akiyama, J. Gahl, K. Rathbun and M. Hagler).
Abstract:  Not Available
+ Modeling of Self-Breakdown Voltage Statistics in High Energy Spark Gaps
  "Modeling of Self-Breakdown Voltage Statistics in High Energy Spark Gaps," J. Appl. Phys. 57, 4981 (1985) (with A.L. Donaldson and M.O. Hagler).
Abstract:  Not Available
+ Wall Effects on the Propagation of Compressional Alfven Waves in a Cylindrical Plasma with Two Ion Species
  "Wall Effects on the Propagation of Compressional Alfven Waves in a Cylindrical Plasma with Two Ion Species," IEEE Trans. Plasma Sci. PS-13, 125 (1985) (with H. Akiyama and M.O. Hagler).
Abstract:  Not Available
Publication Year:  1984
+ A Review of Opening Switch Technology for Inductive Energy Storage
  "A Review of Opening Switch Technology for Inductive Energy Storage," Proc. IEEE 72, 1019 (1984) (with K.H. Schoenbach and G. Schaefer).
Abstract:  Not Available
+ Electrode Erosion Phenomena in a High Energy Pulsed Discharge
  "Electrode Erosion Phenomena in a High Energy Pulsed Discharge," IEEE Trans. Plasma Sci. PS-12, 28 (1984) (with A. Donaldson, M. Hagler, G. Jackson and L. Hatfield).
Abstract:  Not Available
+ Electron Beam Tetrode for Multiple, Submicrosecond Pulse Operation
  H. Harjes, K. Schoenbach, G. Schaefer, M. Kristiansen, H. Krompholz, D. Skaggs, "Electron Beam Tetrode for Multiple, Submicrosecond Pulse Operation", Rev. Sci. Instrum. 55 (1984) 1684
Abstract:  Not Available
+ Investigations of E-Beam Controlled Diffuse Discharges
  K. Schoenbach, G. Schaefer, M. Kristiansen, H. Krompholz, H. Harjes, D. Skaggs, "Investigations of E-Beam Controlled Diffuse Discharges" in "Gaseous Dielectrics IV", ed. L. G. Christophorou, Pergamon Press 1984, p. 246
Abstract:  Not Available
+ Nanosecond Current Probe for High Voltage Experiments
  H. Krompholz, J. Doggett, K. Schoenbach, J. Gahl, C. Harjes, G. Schaefer, M. Kristiansen, "Nanosecond Current Probe for High Voltage Experiments", Rev. Sci. Instrum. 55 (1984) 127
Abstract:  Not Available
+ Nanosecond, Pulsed Breakdown of N2 and SF6
  M. Giesselmann, W. Pfeiffer, J. Wolf, "Nanosecond, Pulsed Breakdown of N2 and SF6", Conference on Electrical Insulation and Dielectric Phenomena", CEIDP, Clayton, Delaware, Conference Record, p. 343-348, 1984.
Abstract:  Not Available
+ Pulsed Hollow-Cathode Discharge with Nanosecond Risetime
  G. Schaefer, P. Husoy, K. Schoenbach, H. Krompholz, "Pulsed Hollow-Cathode Discharge with Nanosecond Risetime", IEEE Trans. Plasma Sci., vol. PS-12 (1984) 271
Abstract:  Not Available
+ Surface Studies of Dielectric Materials Used in Spark Gaps
  "Surface Studies of Dielectric Materials Used in Spark Gaps," J. Appl. Phys. 55, 262 (1984) (with G. Jackson, L. Hatfield, M. Hagler, J. Marx, A. Donald­son, G. Leiker, R. Curry, R. Ness, L. Gordon and D. Johnson).
Abstract:  Not Available
+ The Use of Attachers in Electron-Beam Sustained Discharge Switches - Theoretical Considerations
  G. Schaefer, K. Schoenbach, H. Krompholz, M. Kristiansen, A.H. Guenther, "The Use of Attachers in Electron-Beam Sustained Discharge Switches - Theoretical Considerations", Laser and Particle Beams 2 (1984) 273
Abstract:  Not Available
Publication Year:  1983
+ Pulse Flashover of Solid Dielectrics in Vacuum
  "Pulse Flashover of Solid Dielectrics in Vacuum," IEEE Trans. Elect. Insul. EI-18, 310 (1983) (with G. Jackson, L. Hatfield, J. Marx and A. Bowling).
Abstract:  Not Available
Publication Year:  1982
+ Concepts for Optical Control of Diffuse Discharge Opening Switches
  "Concepts for Optical Control of Diffuse Discharge Opening Switches," IEEE Trans. Plasma Sci. PS-10, 246 (1982) (with K.H. Schoenbach, G. Schaefer, L.L. Hatfield and A.H. Guenther).
Abstract:  Not Available
+ Guest Editorial
  Guest Editorial, IEEE Trans. Plasma Sci. PS-10, 217 (1982) (with A.H. Guenther, M.F. Rose, and J.E. Thompson).
Abstract:  Not Available
+ Investigations of Reed Switch Dynamics and Discharge Phenomena When Switching Intermediate and Heavy Loads
  "Investigations of Reed Switch Dynamics and Discharge Phenomena When Switching Intermediate and Heavy Loads," IEEE Trans. Components, Hybrids and Manu­facturing Techn. CHMT-5, 231 (1982) (with B. Miedzinski).
Abstract:  Not Available
+ Material Studies in a High Energy Spark Gap
  "Material Studies in a High Energy Spark Gap" IEEE Trans. Plasma Sci. PS-10, 286 (1982) (with L.B. Gordon, M.O. Hagler, H.C. Kirbie, R.M. Ness, L.L. Hatfield and J. Marx).
Abstract:  Not Available
+ Space Charge Effects in a Laser-Fiber Optics Triggered Multichannel Spark Gap
  "Space Charge Effects in a Laser-Fiber Optics Triggered Multichannel Spark Gap," IEEE Trans. Plasma Sci. PS-10, 261 (1982) (with H.C. Harjes, E.E. Kunhardt, L.L. Hatfield and A.H. Guenther).
Abstract:  Not Available
+ The Effect of Space Charge Induced by an Electron Beam on Spark Gap Operation
  "The Effect of Space Charge Induced by an Electron Beam on Spark Gap Operation" IEEE Trans. Plasma Sci. PS-10, 234 (1982) (with Y.H. Tzeng, E.E. Kunhardt and A.H. Guenther).
Abstract:  Not Available
Publication Year:  1981
+ Investigations of Various Probe Sheath Materials in the Texas Tech Tokamak
  "Investigations of Various Probe Sheath Materials in the Texas Tech Tokamak," IEEE Trans. Plasma Sci. PS-9, 123 (1981) (with P.D. Coleman, B.D. Blackwell and M.O. Hagler).
Abstract:  Not Available
Publication Year:  1980
+ An Electron Beam Triggered Spark Gap
  "An Electron Beam Triggered Spark Gap," IEEE Trans. Plasma Sci. PS-8, 181 1980) (with K. McDonald, M. Newton, E. Kunhardt and A.H. Guenther).
Abstract:  Not Available
+ Basic Concepts in Electromagnetic Theory
  "Basic Concepts in Electromagnetic Theory", Acad. Amer. Ency., Arete Publ. Co., Princeton, NJ (1980) (with A. Engelhardt).
Abstract:  Not Available
+ Electro-Optical Surface Flashover Measurement
  "Electro-Optical Surface Flashover Measurement," Appl. Phys. Lett. 37, 574 (1980) (with J.E. Thompson, J. Lin and K. Mikkelson).
Abstract:  Not Available
+ Guest Editorial
  Guest Editorial, IEEE Trans. Plasma Sci. PS-8, 129 (1980) (with A.H. Guenther).
Abstract:  Not Available
+ Investigations of Fast Insulator Surface Flashover in Vacuum
  "Investigations of Fast Insulator Surface Flashover in Vacuum," IEEE Trans. Plasma Sci. PS-8, 191 (1980) (with J.E. Thompson, J. Lin and K. Mikkelson).
Abstract:  Not Available
+ Laser Triggering through Fiber Optics of a Low Jitter Spark Gap
  "Laser Triggering through Fiber Optics of a Low Jitter Spark Gap," IEEE Trans. Plasma Sci. PS-8, 170 (1980) (with H.C. Harjes, L. Hatfield, K.H. Schoenbach and A.H. Guenther).
Abstract:  Not Available
Publication Year:  1979
+ A New Nanosecond Surface Flashover Diagnostic Technique
  "A New Nanosecond Surface Flashover Diagnostic Technique," J. Japan Res. Soc. for Elec. Discharges (JRED), No. 78, 73 (1979).
Abstract:  Not Available
+ A Review of High Power Switch Technology
  "A Review of High Power Switch Technology," IEEE Trans. Electron Devices ED-26, 1401 (1979) (with T.R. Burkes, J.P. Craig, M.O. Hagler and W.M. Portnoy).
Abstract:  Not Available
+ Beat Heating in Plasmas Using CO2 Lasers
  "Beat Heating in Plasmas Using CO2 Lasers," J. de Physique, Colloque C7, suppl. 7, 40, C7-747 (1979) (with E. Chu, R. Druce, M. Hagler and R. Bengtson).
Abstract:  Not Available
+ Electro-Optical Measurements of Insulator Surface Flashover in Vacuum
  "Electro-Optical Measurements of Insulator Surface Flashover in Vacuum," J. de Physique, Colloque C7, suppl. 7, 40, C7-401 (1979) (with K. Mikkelson, J. Lin and J. Thompson).
Abstract:  Not Available
+ Fast Wave Resonances Near the Ion Cyclotron Frequency
  "Fast Wave Resonances Near the Ion Cyclotron Frequency," IEEE Trans. Plasma Sci. PS-7, 1 (1979) (with R.E. Dollinger and M.O. Hagler).
Abstract:  Not Available
+ Laser/Fiber Optic Breakdown of a Pulse Charged 90% Ar - 10% N2 Gas Switch
  "Laser/Fiber Optic Breakdown of a Pulse Charged 90% Ar - 10% N2 Gas Switch," J. de Physique, Colloque C7, suppl. 7, 40, C7-483 (1979) (with H.C. Harjes, L.L. Hatfield, A.H. Guenther and K.H. Schoenbach).
Abstract:  Not Available
Publication Year:  1977
+ A Numerical Analysis of High Power Laser Propagation in Magnetized Plasmas
  "A Numerical Analysis of High Power Laser Propagation in Magnetized Plasmas," Recent Advances in Plasma Phys., Indian Acad. of Sci., 165, June 1977 (with R. Druce and M.O. Hagler).
Abstract:  Not Available
+ Ablation Rates of Polystyrene Microspheres in a Theta Pinch Plasma
  "Ablation Rates of Polystyrene Microspheres in a Theta Pinch Plasma," J. Appl. Phys. 46, 11 (1977) (with D.L. Smith and M.O. Hagler).
Abstract:  Not Available
Publication Year:  1976
+ Laser Heating of Magnetized Plasma
  "Laser Heating of Magnetized Plasma," Nucl. Fusion 16, 6 (1976) (invited review paper) (with M.O. Hagler).
Abstract:  Not Available
+ Optical Measurements of High Electric and Magnetic Fields
  "Optical Measurements of High Electric and Magnetic Fields," IEEE Trans. Instr. and Meas. IM-25, 1 (1976) (with J.E. Thompson and M.O. Hagler).
Abstract:  Not Available
Publication Year:  1975
+ Differential Measurement of Fast Energy Discharge Capacitor Inductance and Resistance
  "Differential Measurement of Fast Energy Discharge Capacitor Inductance and Resistance," IEEE Trans. Instr. and Meas. IM-24, 112 (1975) (with W.C. Nunnally and M.O. Hagler).
Abstract:  Not Available
+ Helical Antenna for Exciting Azimuthally Asymmetric Alfven Waves
  "Helical Antenna for Exciting Azimuthally Asymmetric Alfven Waves," J. Appl. Phys. 46, 2516 (1975) (with S.O. Knox and F.J. Paoloni).
Abstract:  Not Available
+ Plasma-Solid Interaction in a Theta Pinch
  "Plasma-Solid Interaction in a Theta Pinch," Appl. Phys. Lett. 26, 496 (1975) (with W.C. Nunnally and M.O. Hagler).
Abstract:  Not Available
Publication Year:  1974
+ A Report on the Second Topical Conference on RF Plasma Heating
  "A Report on the Second Topical Conference on RF Plasma Heating," Nucl. Fusion 14, 741 (1974) (with F.J. Paoloni).
Abstract:  Not Available
+ CO2 Laser Heating of a Magnetized Plasma Column
  "CO2 Laser Heating of a Magnetized Plasma Column," Appl Phys. Lett. 24, 583 (1974) (with G.M. Molen, M.O. Hagler and R.D. Bengtson).
Abstract:  Not Available
+ Simple, Multiple Arc, Dielectric Switch Applied to a Theta Pinch
  "Simple, Multiple Arc, Dielectric Switch Applied to a Theta Pinch," Rev. Sci. Inst. 45, 1361 (1974) (with W.C. Nunnally and M.O. Hagler).
Abstract:  Not Available
Publication Year:  1973
+ A Report on the Texas Symposium on the Technology of Controlled Thermonuclear Fusion Experiments and the Engineering Aspects of Fusion Reactors
  "A Report on the Texas Symposium on the Technology of Controlled Thermonuclear Fusion Experiments and the Engineering Aspects of Fusion Reactors," Nucl. Fusion 13, 281 (1973).
Abstract:  Not Available
+ CO2 Laser Beam Refraction in a Linear Discharge Plasma
  "CO2 Laser Beam Refraction in a Linear Discharge Plasma," Appl. Phys. Lett. 23, 601 (1973) (with G.M. Molen and M.O. Hagler).
Abstract:  Not Available
+ Exploding Wires in Strong Axial Magnetic Fields
  "Exploding Wires in Strong Axial Magnetic Fields," J. Appl. Phys. 44, 1923 (1973) (with E.M. Honig and M.O. Hagler).
Abstract:  Not Available
Publication Year:  1972
+ A Holographic Data Storage System Design Project
  "A Holographic Data Storage System Design Project," Int. J. Elec. Engrg. Educ. 10, 296 (1972) (with R.M. David, C.R. Parten and M.O. Hagler).
Abstract:  Not Available
+ An Azimuthally Symmetric, Unidirectional Ion Cyclotron Wave Exciter
  "An Azimuthally Symmetric, Unidirectional Ion Cyclotron Wave Exciter," J. Appl. Phys. 43, 3590 (1972) (with J.E. Hipp and M.O. Hagler).
Abstract:  Not Available
+ CO2 Laser Design and Laboratory Projects
  "CO2 Laser Design and Laboratory Projects," IEEE Trans. Educ. E-15, 51 (1972) (with G.M. Molen, R.H. Trotter and M.O. Hagler).
Abstract:  Not Available
+ Fast Wave Damping at the Second Harmonic of the Ion Cyclotron Frequency
  "Fast Wave Damping at the Second Harmonic of the Ion Cyclotron Frequency," Phys. Lett. A40, 141 (1972) (with J.E. Cato, M.O. Hagler and C.N. Watson­-Munro).
Abstract:  Not Available
+ Some Engineering Problems of Low Frequency Heating of Fusion Reactors
  "Some Engineering Problems of Low Frequency Heating of Fusion Reactors," Nucl. Fusion 12, 345 (1972) (with J.E. Cato and M.O. Hagler).
Abstract:  Not Available
Publication Year:  1971
+ Fusion Reactor Design, Nuclear Power: The 1970's
  "Fusion Reactor Design, Nuclear Power: The 1970's," Professional Engineer 41, 2, Feb. 1971 (with M.O. Hagler).
Abstract:  Not Available
+ Global Temperature Effects of the Use of Fusion Energy and the Fusion Torch
  "Global Temperature Effects of the Use of Fusion Energy and the Fusion Torch," IEEE Trans. Nucl. Sci. 18, 31 (1971), (with W.A. Porter and M.O. Hagler).
Abstract:  Not Available
+ Heat Shrinkable Tubing as an Inexpensive Vacuum Seal
  "Heat Shrinkable Tubing as an Inexpensive Vacuum Seal," J. Vacuum Sci. and Techn. 8, 515 (1971) (with G.M. Molen, L.G. Roseland and M.O. Hagler).
Abstract:  Not Available
+ Travelling Wave Antenna for Exciting Waves in Cylindrical Anisotropic Plasma
  "Travelling Wave Antenna for Exciting Waves in Cylindrical Anisotropic Plasma," J. Appl. Phys. 42, 4887 (1971) (with M.O. Hagler and J.E. Hipp).
Abstract:  Not Available
Publication Year:  1970
+ An Optical Data Processing Experiment for E.E. Students
  "An Optical Data Processing Experiment for E.E. Students," IEEE Trans. Educ. E-13, 60 (1970) (with L.N. Peckham and M.O. Hagler).
Abstract:  Not Available
+ Arc Welding Generators Used as Air Core Magnet Power Supplies
  "Arc Welding Generators Used as Air Core Magnet Power Supplies," Rev. Sci. Instr. 41, 1322 (1970) (with J.E. Cato, J.E. Hipp and M.O. Hagler).
Abstract:  Not Available
+ Industrial Applications of Lasers
  "Industrial Applications of Lasers," ISA Trans. 9, 216 (1970) (with L.N. Peckham and M.O. Hagler).
Abstract:  Not Available
+ Inexpensive, Fast On-Off, High Power, Pulsed RF Amplifier
  "Inexpensive, Fast On-Off, High Power, Pulsed RF Amplifier," Rev. Sci. Instr. 41, 1903 (1970) (with R.D. Melton, J.E. Cato and M.O. Hagler).
Abstract:  Not Available
+ Laser Laboratory Projects for Undergraduates
  "Laser Laboratory Projects for Undergraduates," Engrg. Educ. 60, 899, (1970) (with L.N. Peckham and M.O. Hagler)
Abstract:  Not Available
Publication Year:  1969
+ Foreign Students in American Universities
  "Foreign Students in American Universities," Engrg. Educ. 59, 1135 (1969).
Abstract:  Not Available
+ Stop- and Pass-Bands for Harmonic Ion Cyclotron Waves
  "Stop- and Pass-Bands for Harmonic Ion Cyclotron Waves," Plasma Phys. 11, 19 (1969) (with A.A. Dougal).
Abstract:  Not Available
+ The Use of Hamilton's Modified Principle to Solve Nonlinear Control Problems
  "The Use of Hamilton's Modified Principle to Solve Nonlinear Control Problems," ISA Trans. 8, 329 (1969) (with M.O. Hagler and L.G. Clark).
Abstract:  Not Available
Publication Year:  1967
+ Experimental Investigation of Harmonic Ion Cyclotron Wave Propagation and Attenuation
  "Experimental Investigation of Harmonic Ion Cyclotron Wave Propagation and Attenuation," Phys. Fluids 10, 596 (1967) (with A.A. Dougal).
Abstract:  Not Available
+ Inexpensive, High Vacuum, Electric Feed-Through
  "Inexpensive, High Vacuum, Electric Feed-Through," Rev. Sci. Instr. 38, 840 (1967) (with J.G. Melton and A.A. Dougal).
Abstract:  Not Available
Publication Year:  1966
+ Evaluation of Faraday-Shielded Stix Coils for Ion Cyclotron Resonance Heating of a Plasma
  "Evaluation of Faraday-Shielded Stix Coils for Ion Cyclotron Resonance Heating of a Plasma," Rev. Sci. Instr. 37, 1455 (1966) (with N.B. Dodge and A.A. Dougal).
Abstract:  Not Available
Publication Year:  1963
+ Hamilton's Modified Principle Applied to Nonlinear Circuit Problems
  "Hamilton's Modified Principle Applied to Nonlinear Circuit Problems," IEEE Trans. Comm. and Circuit Theory 69, 598 (1963) (with L.G. Clark).
Abstract:  Not Available