Center for Pulsed Power and Power Electronics.
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Dr. Magne Kristiansen

C.B. Thornton/P.W. Horn Professor

Contact Information

Department of Electrical and Computer Engineering
Texas Tech University
Lubbock, TX 79409-3102

Phone: (806)742-2224
Fax: (806)742-1281
M.kristiansen@ttu.edu

Education

Research Interests

Experience

Projects

Awards and Professional Societies

Publications


Journal

Publication Year:  2008
+ 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:  Not Available
+ 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
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

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+ 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

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+ 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

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Publication Year:  2006
+ 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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+ 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
+ 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
+ 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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+ 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.

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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
+ 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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+ 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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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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+ 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.

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+ 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
+ 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
+ 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
+ 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.

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+ 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

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+ 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.

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+ 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
+ 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

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+ 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
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

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+ 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, 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
+ 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

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+ 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

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+ 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
+ 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

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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

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+ 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
+ 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

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+ 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
Publication Year:  1998
+ 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

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+ 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

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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
+ 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
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
Publication Year:  1993
+ 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</