Center for Pulsed Power and Power Electronics.
TTU Home Edward E. Whitacre Jr. College of Engineering P3E Home Faculty

Dr. James Dickens, Professor

Contact Information

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

Phone: (806)742-1254
Fax: (806)742-1245
James.Dickens@ttu.edu

Education

Research Interests

Other Interests

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
+ Compact High Power Microwave Generation
  Neuber, A. Young, M. Elsayed, J. Dickens, M. Giesselmann, M. Kristiansen, L. Altgilbers, Compact High Power Microwave Generation, Proceedings of the 2008 Army Science Conference, Orlando Florida, December 1-4, 2008. Presenter, P3E team contribution, paper was invited by L. Altgilbers.
Abstract:  Not Available
+ 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:  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:  Not Available
+ 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:  Not Available
+ 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:  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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+ 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.

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+ 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

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+ 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.

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Publication Year:  2006
+ 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, 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-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.

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+ 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
+ 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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+ 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
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.

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+ 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

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+ 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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+ 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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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
+ 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
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
Publication Year:  2000
+ 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
Publication Year:  1999
+ 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

[PDF]

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

[PDF]

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

Conference Paper/Presentation

Publication Year:  2008
+ A 50 kV, 100 Hz Low Jitter Triggered Spark Gap with High Pressure Gas Mixtures
  Chen, Yeong-Jer; Mankowski, John J.; Dickens, James C.; Walter, John; Kristiansen, Magne; A 50 kV, 100 Hz Low Jitter Triggered Spark Gap with High Pressure Gas Mixtures; IEEE International Power Modulators and High Voltage Conference, Proceedings of the 2008; 27-31 May 2008 Page(s):197 - 200; Digital Object Identifier 10.1109/IPMC.2008.4743614
Abstract:  Not Available
+ A Compact, Self-Contained High Power Microwave Source Based on a Reflex-Triode Vircator and Explosively Driven Pulsed Power
  A. Young, T. Holt, M. Elsayed, J. Walter, J. Dickens, A. Neuber, M. Kristiansen, L.L. Altgilbers, and A.H. Stults, A Compact, Self-Contained High Power Microwave Source Based on a Reflex-Triode Vircator and Explosively Driven Pulsed Power, to be published in the Proceedings of the 2008 IEEE International Power Modulator Conference Las Vegas, Nevada, USA, May 27-31, 2008.
Abstract:  Not Available
+ Analysis of Mesoband Single Element Pulsed Ring-Down Antennas for Implementation in Phased Array Systems
  Belt, D.; Mankowski, J.; Walter, J.; Dickens, J.; Kristiansen, M.; IEEE International Power Modulators and High Voltage Conference, Proceedings of the 2008 27-31 May 2008 Page(s):152 - 155 Digital Object Identifier 10.1109/IPMC.2008.4743602
Abstract:  Not Available
+ Compact High Power Microwave Generation
  A. Neuber, A. Young, M. Elsayed, J. Dickens, M. Giesselmann, M. Kristiansen, L.L. Altgilbers, Compact High Power Microwave Generation, 26th Army Science Conference, (Orlando, FL, USA), November 2008, to be published.
Abstract:  Not Available
+ Compact Silicon Carbide Switch For High Voltage Operation
  James, C.; Hettler, C.; Dickens, J.; Neuber, A.; Compact Silicon Carbide Switch For High Voltage Operation; IEEE International Power Modulators and High Voltage Conference, Proceedings of the 2008 27-31 May 2008 Page(s):17 - 20 Digital Object Identifier 10.1109/IPMC.2008.4743565
Abstract:  Not Available
+ Comparison of HFCG and Compact Marx for Driving a High Power Microwave Load
  A. Neuber, A. Young, M. Elsayed, J. Walter, J. Dickens, M. Giesselmann, M. Kristiansen,and L.L. Altgilbers, Comparison of HFCG and Compact Marx for Driving a High Power Microwave Load, 12th IEE Conference on Megagauss Magnetic Field Generation, (Novosibirsk, Russia), July 2008, to be published.
Abstract:  Not Available
+ Energy Deposition and Electromagnetic Compatibility Assessment of Electroexplosive Devices
  Parson, J.; Dickens, J.; Walter, J.; Neuber, A.; IEEE International Power Modulators and High Voltage Conference, Proceedings of the 2008 27-31 May 2008 Page(s):439 - 442 Digital Object Identifier 10.1109/IPMC.2008.4743684
Abstract:  Not Available
+ High-Current Compact FCG Seed Source Implementing Solid State Switching
  M. Elsayed, T. Holt, A. Young, A. Neuber, J. Dickens, M. Kristiansen, L.L. Altgilbers, and A.H. Stults, High-Current Compact FCG Seed Source Implementing Solid State Switching, to be published in the Proceedings of the 2008 IEEE International Power Modulator Conference Las Vegas, Nevada, USA, May 27-31, 2008.
Abstract:  Not Available
+ Jitter and recovery rate of a 50 kV, 100 Hz 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 50 kV, 100 Hz triggered spark gap with high pressure gas mixtures; Plasma Science, 2008. ICOPS 2008. IEEE 35th International Conference on 15-19 June 2008 Page(s):1 - 1 Digital Object Identifier 10.1109/PLASMA.2008.4590809
Abstract:  Not Available
+ Opening Switch Utilizing Stress Induced Conduction In PMMA
  C. Lynn, A. Neuber, J. Dickens, J. Krile, Opening Switch Utilizing Stress Induced Conduction In PMMA, presented at the 2008 IEEE International Power Modulator Conference Las Vegas, Nevada, USA, May 27-31, 2008.
Abstract:  Not Available
+ Scaling and Improvement of Compact Explosively-Driven Ferroelectric Generators,
  D. Bolyard, A. Neuber, J. Krile, J. Walter, J. Dickens, and M. Kristiansen, Scaling and Improvement of Compact Explosively-Driven Ferroelectric Generators, to be published in the Proceedings of the 2008 IEEE International Power Modulator Conference Las Vegas, Nevada, USA, May 27-31, 2008.
Abstract:  Not Available
+ Shock Wave Simulation of Ferrite-Filled Coaxial Nonlinear Transmission Lines
  Sullivan, W.; Dickens, J.; Kristiansen, M.; Shock Wave Simulation of Ferrite-Filled Coaxial Nonlinear Transmission Lines; IEEE International Power Modulators and High Voltage Conference, Proceedings of the 2008 27-31 May 2008 Page(s):517 - 520 Digital Object Identifier 10.1109/IPMC.2008.4743706
Abstract:  Not Available
+ Window Flashover Initiation Under Pulsed Microwave Excitation
  J. Krile, G. Edmiston, J. Dickens, H. Krompholz, and A. Neuber, Window Flashover Initiation Under Pulsed Microwave Excitation, to be published in the Proceedings of the 2008 IEEE International Power Modulator Conference Las Vegas, Nevada, USA, May 27-31, 2008.
Abstract:  Not Available
Publication Year:  2007
+ Electro-Explosive Fuse Optimization for Helical Flux Compression Generator Using a Non-Explosive Test Bed
  D. McCauley, D. Belt, J. Mankowski, J. Dickens, A. Neuber, M. Kristiansen, "Electro-Explosive Fuse Optimization for Helical Flux Compression Generator Using a Non-Explosive Test Bed," presented at the 2007 IEEE Pulsed Power and Plasma Science Conference, Albuquerque, NM June 17-22, 2007.
Abstract:  Helical Flux Compression Generators (HFCG) of 50 mm form factor have been shown to produce a maximum energy deposit of 3 kJ into a 3 muH inductor from a seed current. A large dl/dt into a coupled load is possible when an electro-explosive fuse is used. Previous work with a non-optimized fuse has produced ~100 kV into a 15Omega load which leads into a regime relevant for High Power Microwave (HPM) systems. It is expected that ~3()0kV can be achieved with the present 2 stage HFCG driving an inductive storage system with an electro-exploding fuse. In order to optimize the electro-explosive fuse design, a non-explosive test bed, which closely simulates the 45 kA HFCG output, is used. To optimize the tiise, effects of fuse material, fuse length, and fuse shape will be examined as well as the effects of various quenching materials. Our previous work has characterized fuse material but we are also looking into the effects of the processes used to create the fuse wire, such as tempered wire versus fully annealed wire. Additionally, to maximize the output voltage and minimize the fuse recovery time, we are optimizing the length of the fuse wire. For shorter fuse lengths, we are optimizing fuse shape as well as fuse length to find the best fuse recovery time. By optimizing the individual parameters of an electro-explosive fuse, the fuse as a whole will be optimized to produce maximum output voltage when used with an HFCG.

[PDF]

+ Modeling of a Single Element Pulsed Ring-Down Antenna for Implementation in a Phased Array System
  Belt, D.; Walter, J.; Mankowski, J.; Dickens, J.; Modeling of a Single Element Pulsed Ring-Down Antenna for Implementation in a Phased Array System; Pulsed Power Plasma Science, 2007. PPPS 2007. Conference Record - Abstracts. IEEE 17-22 June 2007 Page(s):816 - 816
Abstract:  Summary form only given. A pulsed ring-down phased array antenna provides substantial energy deposition in the far field region in addition to a broad range main beam with scanning capabilities. This allows remote neutralization of Improvised explosive devices (IEDs) at far field distances and in virtually any direction. The pulsed ring-down antenna operates by charging the single element antenna with a high potential source and closing a switch to develop transient wave reflections on the antenna which then propagate in air. The performance of a pulsed ring-down phased arrav is highly contingent upon the design and performance of the individual antenna elements within the array. Such factors as operating voltage, antenna capacitance, material losses, antenna geometry and closing switch conductance characteristics must be examined for optimal performance to be achieved. By utilizing the Comsol RF module transient analysis functions, we are able to characterize the various parameters beginning with a monopole and a dipole pulsed ring-down antenna operating in the hundreds of MHz range. We have examined and compared the results achieved from the experimental setup to the simulation model in order to better characterize the individual components of the antenna. We have also examined the discrepancies between an ideal closing switch and the experimental setup closing switch, which dramatically affects the far field range of the antenna. We have examined the material properties of the antenna to improve losses and increase system capacitance allowing an increase in the number of RF cycles per antenna discharge. With the results presented, an accurate model of pulsed ring-down antennas is available and will allow future development of more complex geometries that will improve the operation of pulsed ring- down phased array.

[PDF]

+ Opening Switch Utilizing Shock Wave Induced Conduction in PMMA and PVC
  C. Lynn, A. Neuber, J. Dickens, "Opening Switch Utilizing Shock Wave Induced Conduction in PMMA and PVC," presented at the 2007 IEEE Pulsed Power and Plasma Science Conference, Albuquerque, NM June 17-22, 2007
Abstract:  Not Available
+ Theoretical Pulsed Ring Down Antenna Array Performance
  Walter, J.; Dickens, J.; Mankowski, J.; Kristiansen, M.; Theoretical Pulsed Ring Down Antenna Array Performance Pulsed Power Plasma Science, 2007. PPPS 2007. Conference Record - Abstracts. IEEE 17-22 June 2007 Page(s):482 - 482
Abstract:  Summary form only given. High-power transient RF transmitters are currently being developed for multiple applications. One potential high- power pulsed source being considered is the pulsed ring- down source (PRDS). In a typical PRDS, electrical energy that is stored in the device structure is discharged through a switch, generating a damped ringing radiated waveform. The magnitude of the transmitted field is limited by parameters such as the overall device geometry and switch characteristics. The potential exists to increase the radiated far field power density by utilizing an array of PRDS transmitters. The performance of such an array depends on the triggering jitter of the device switches and the design of the individual radiating elements. The application of the array concept to pulsed ring-down sources using gas spark gap switches is examined. Theoretical array performance is discussed, taking into account practical switch jitter distributions, practical switch triggering schemes, and individual element characteristics.

[PDF]

Publication Year:  2006
+ A Flux Compression Generator Non-Explosive Test Bed for Explosive Opening Switches
  Belt, D.; Mankowski, J.; Neuber, A.; Dickens, J.; Kristiansen, M.; Conference Record of the 2006 Twenty-Seventh International Power Modulator Symposium, 2006. 14-18 May 2006 Page(s):456 - 459
Abstract:  Helical flux compression generators (HFCG) of a 50 mm form factor have been shown to produce output energies on the order of ten times the seeded value and a typical deposited energy of 3 kJ into a 3 muH inductor. Our previous work with a non-optimized fuse has produced-100 kV into a 15 load, which leads into a regime relevant for high power microwave (HPM) systems. It is expected that-300 kV can be achieved with the present 2-stage HFCG driving an inductive storage system with electro-exploding fuse. In order to optimize the electro-explosive wire fuse, we have constructed a non-explosive test bed which simulates the HFCG output with high accuracy. We have designed and implemented a capacitor based, magnetic switching scheme to generate the near exponential rise of the HFCG. The varying inductance approach utilizes 4 stages of inductance change and is based upon a piecewise linear regression model of the HFCG waveform. The non-explosive test bed will provide a more efficient method of component testing and has demonstrated positive initial fuse results

[PDF]

+ Contributing Factors to Window Flashover Under Pulsed High Power Microwave Excitation at High Altitude
  Edmiston, G.; Neuber, A.; Krile, J.; McQuage, L.; Krompholz, H.; Dickens, J.; 2006 Power Modulator Symposium, Conference Record of the 2006 Twenty-Seventh International May 2006 Page(s):389 - 392
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 technical 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 Torr to 90 Torr) 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.

[PDF]

+ Dielectric Surface Flashover Research at Texas Tech University
  A. Neuber, H. Krompholz, J. Dickens, M. Kristiansen, “Dielectric Surface Flashover Research at Texas Tech University,” presented at the 1st Euro-Asian Pulsed Power Conference, Sept. 18 -22, 2006, Chengdu, China.
Abstract:  Not Available
+ Electro-explosive fuse development for helical flux compression generators
  D. Belt, J. Dickens, J. Mankowski, A. Neuber, and M. Kristiansen, “Electro-explosive fuse development for helical flux compression generators,” presented at the 2006 International Conference on Megagauss Magnetic Field Generation and Related Topics, November 5-10, 2006 Santa Fe, New Mexico, USA
Abstract:  Not Available
+ Helical Flux Compression Generator Non- Explosive Test Bed for Electro-Explosive Fuses
  D. Belt, J. Dickens, J. Mankowski, A. Neuber, M. Kristiansen, “Helical Flux Compression Generator Non- Explosive Test Bed for Electro-Explosive Fuses”, presented at the 27th Power Modulator Symposium and 2006 High Voltage Workshop May 14-18, 2006, Washington, DC.
Abstract:  Not Available
+ Interface Breakdown During High Power Microwave Transmission
  A. Neuber, J. Krile, G. Edmiston, H. Krompholz, J. Dickens, M. Kristiansen ,“Interface Breakdown During High Power Microwave Transmission,” presented at the 13th EML Symposium, May 22-25, 2006, Berlin, Germany.
Abstract:  Not Available
+ Pressure Induced Conductivity for High Power Switching
  Veselka, H.; Neuber, A.; Dickens, J.; Power Modulator Symposium, 2006. Conference Record of the 2006 Twenty-Seventh International 14-18 May 2006 Page(s):219 - 219
Abstract:  Summary form only given. Investigations of shock induced conductivity of non-crystalline insulators and crystalline semiconductors were performed. Although we measured the insulator-to-metallic state transition time and conductivity, the focus of this investigation was on the recovery phase of the induced conductivity (i.e. metallic-to-insulator state transition). The recovery time and shock conditions were measured with high speed electrical diagnostics. The goal of this research is to determine the feasibility of using shock induced conductivity as a means of producing a high power opening switch. To minimize switch losses, the insulator-to-metallic transition time and conductance is also important, but has been more widely studied. Initial impact studies have shown that certain insulator can be conductive for 100 microseconds and recover under modest voltage less than one microsecond using a ten gram explosive charge. Various shock intensities are used in the study. The shock is produced primarily with conventional commercial explosives. In addition, the impact of sample thickness and compression duration on the induced the conductivity were also studied. The correlation between modest voltage and high voltage recovery time and shut-off current were studied

[PDF]

+ Pulsed Unipolar Surface Flashover at Atmospheric Conditions
  Morales, K.; Krile, J.; Neuber, A.; Krompholz, H.; Dickens, J.; Power Modulator Symposium, 2006. Conference Record of the 2006 Twenty-Seventh International 14-18 May 2006 Page(s):174 - 180
Abstract:  Dielectric surface flashover along insulators in vacuum has been comprehensively researched over the years. However, the primary mechanisms involved in dielectric flashover at atmospheric pressures have yet to be as extensively analyzed with variable parameters such as electrode geometry, background gas, humidity, and temporal characteristics of the applied voltage. Understanding the fundamental physical mechanisms involved in surface flashover at atmospheric pressures is vital to characterizing and modeling the arc behavior. Previous DC and unipolar excitation experiments have shown distinct arc behavior in air and nitrogen environments for an electrode geometry that produces electric field lines that curve above the dielectric surface. Specifically, flashover arcs in an air environment were observed to develop along the dielectric surface. Experiments conducted in nitrogen revealed that the arc developed along the electric field lines, above the surface of the dielectric. It was also of importance to alter the temporal characteristics of the applied voltage to simulate lightning situations and investigate the impact on the arc behavior and voltage delay times. A solid state high voltage pulser with an adjustable pulse width of ~500 ns at FWHM and amplitudes in excess of 30 kV was specifically developed to replicate the temporal characteristics of a voltage pulse observed when a building structure is hit by a lightning strike. Based on these results, the physical mechanisms primarily involved in pulsed unipolar surface flashover will be discussed. Additional studies regarding the effects of humidity and surface roughness on the flashover arc behavior will also be presented

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+ The Impact of Water Conductivity, Electrode Material, and Electrode Surface Roughness on the Pulsed Breakdown Strength of Water
  Wetz, D.; Mankowski, J.; McCauley, D.; Dickens, J.; Kristiansen, M.; Conference Record of the 2006 Twenty-Seventh International Power Modulator Symposium, 2006. 14-18 May 2006 Page(s):104 - 107
Abstract:  Experimental results are presented on the impact water conductivity, electrode material, and electrode surface roughness have on the dielectric strength of water. A 2 mm water gap was tested under pulsed conditions with maximum electric fields in excess of 1.5 MV/cm. Bruce profiled electrodes manufactured from various materials including molybdenum, aluminum, copper, tungsten, nickel, stainless steel, and zinc oxide, which have work functions ranging from 4.2 eV to 5.3 eV, have been tested. The roughness average of the various surfaces was varied from 0.1 mum to 1.96 mum and the conductivity of the water within the gap was varied from 1muS/cm to 39 muS/cm to determine the impact each has when tested in combination with the various electrode materials and surface roughnesses. Conclusions are made as to the effect each of these factors has on the holdoff strength of a water dielectric system

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Publication Year:  2005
+ A Compact, Repetitive, 500kV, 500 J, Marx Generator
  Neuber, A.A.; Chen, Y.J.; Dickens, J.C.; Kristiansen, M.; 2005 IEEE Pulsed Power Conference; June 2005 Page(s):1203 - 1206
Abstract:  The electrical characteristics and design features of a low inductance, compact, 500 kV, 500 J, 10 Hz repetition rate, Marx generator are discussed. While benefiting from the large energy density of mica capacitors, 4 mica capacitors were utilized in parallel per stage, keeping the parasitic inductance per stage low. Including the spark-gap switches, a stage inductance of 55 nH was measured, which translates with 100 nF capacitance per stage to ~ 18.5 Âż characteristic Marx impedance. Using solely inductors, ~ 1 mH each, as charging elements instead of resistors enabled charging the Marx within less than 100 ms with little charging losses. The pulse width of the Marx into a matched resistive load is about 200 ns with 50 ns rise-time. Repetitive HPM generation with the Marx directly driving a small Vircator has been verified. The Marx is fitted into a tube with 30 cm diameter and a total length of 0.7 m. We discuss the Marx operation at up to 21 kV charging voltage per stage, with repetition rates of up to 10 Hz in burst mode primarily into resistive loads. A lumped circuit description of the Marx is also given, closely matching the experimental results.

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+ A Low-Cost Metallic Cathode for a Vircator HPM Source
  Y.J. Chen, J.J. Mankowski, A. Neuber, J.C. Dickens, “A Low-Cost Metallic Cathode for a Vircator HPM Source,” Proceedings of the 15th Int. IEEE Pulsed Power Conference, pp. 66-69, Monterey, CA, June 13-17, 2005
Abstract:  Not Available
+ A Low-Cost Metallic Cathode for a Vircator HPM Source
  Mankowski, J.; Chen, Y.; Dickens, J.; Neuber, A.; Gale, R.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):66 - 69
Abstract:  Recent research efforts at TTU include the testing of a rapidly charged, rep-rated Marx generator driving a reflex triode vircator [1]. As expected, the burning of the cathode material (ordinary cloth velvet), was the primary failure mechanism during repetitive operation. In an effort to achieve a repetitive vircator (>10 Hz), we are exploring a low-cost, all-metal cathode. The cathode is made from aluminum with a patterned surface. A typical pattern is composed of peaks and troughs with dimensions on the order of tens of microns. The pattern is achieved with a simple, low-cost chemical etching process. Results include current, voltage, and microwave waveforms from two solid metal cathodes and a cloth velvet cathode.

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+ Bubble Dynamics and Channel Formation for Cathode Initiated Discharges in Transformer Oil
  Cevallos, M.; Butcher, M.; Dickens, J.; Neuber, A.; Krompholz, H.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):1235 - 1238
Abstract:  The development of cathode initiated low density channel formation and propagation leading to self breakdown in transformer oil is investigated using high speed electrical and optical diagnostics in a coaxial system with a point/plane axial discharge at various hydrostatic pressures. A cathode initiated channel formation and propagation model based upon single bubble dynamics has been presented by Kattan [1]. Experiments based on high-speed shadowgraphy were conducted to decide if the principles that govern single bubble dynamics could be applied to cathode initiated channel formation. These experiments show bubble motion away from the cathode, with separation velocities on the order of 10's m/s. This separation is similar for single bubbles generated at the cathode and for bubble chains developing into low-density channels. Lifetimes of these channels are recorded and show good correlation with the Rayleigh model [2] used to predict lifetimes of single bubbles. Experiments at reduced hydrostatic pressure reveal a critical pressure below which low density channel expansion occurs, further corroborating the presence of a gas phase. Finally, the pressure dependence of the breakdown voltage due to the expansion of the low density channels is examined and a model for this dependence is presented. The experiments conducted confirm the presence of a gas phase channel, its correlation with single bubble dynamics, and its importance to final breakdown.

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+ Characaterization of Transient Antennas
  "Characaterization of Transient Antennas", proceeding of the 15th Int’l. Pulsed Power Conference, Monterey, CA, June 13-17, 2005 (with J. Walter and J. Dickens).
Abstract:  Not Available
+ Compact Pulsed Power at TTU
  A. Neuber, M. Kristiansen, J. Dickens, M. Giesselmann, “Compact Pulsed Power at TTU,” 3rd Annual Multi-Functional Warhead Workshop, 30 November – 1 December 2005, Redstone Arsenal, Huntsville, AL.
Abstract:  Not Available
+ Composite Shadowgraphy and Luminosity Images of Self Breakdown Discharge Channels in Transformer Oil
  Cevallos, M.; Butcher, M.; Dickens, J.; Neuber, A.; Krompholz, H.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):982 - 985
Abstract:  The physics of cathode initiated discharge formation leading to self breakdown in transformer oil is investigated using high speed electrical and optical diagnostics in a coaxial system with a point/plane axial discharge. Previous research conducted on self breakdown channel formation using high speed shadowgraphy and photography of the emitted light has shown tree-like structures for both cathode and anode initiated discharges, with characteristic differences. Cathode initiated discharges expand faster to a more "bushy" appearance, whereas anode initiated discharges show branching localized channels. So far, the spatial resolution to detect small luminous areas in pre-breakdown discharges and to determine their correlation to low density regions visible in the shadowgraphs was not sufficient in the experiments described in this paper, thus a systematic variation of exposure times, and time delays between luminosity pictures and shadowgraphy pictures has been performed. These experiments confirm that the luminosity emitted during prebreakdown events is generated from the low density regions seen in the shadowgraphy images, indicating charge amplification mechanisms in the gas phase for cathode initiated events. This statement is further supported by the dependence of both the channel dynamics and the light emission at lowered hydrostatic pressure.

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+ High Power Microwave Breakdown Limits of Dielectric/Gas Interfaces
  A. Neuber, G. Edmiston, J. Krile, K. Morales, J. Dickens, H. Krompholz, "High Power Microwave Breakdown Limits of Dielectric/Gas Interfaces,” presented at the 2005 International COE Forum on Pulsed Power Science held on November 13 – 14 at Kumamoto, Japan. (invited)
Abstract:  Not Available
+ High Power Microwave Surface Flashover of a Gas-Dielectric Interface at 90 to 760 Tor
  Edmiston, G.; Krile, J.; Neuber, A.; Dickens, J.; Krompholz, H.; 2005 IEEEPulsed Power Conference, June 2005 Page(s):350 - 353
Abstract:  The major limiting factor in the transmission of 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 [1]. 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. We will present experimental results, including the impact of gas pressure, and discuss possible causes for the difference in the rf-breakdown field with and without the interface/metallic triple point portion.

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+ Investigation of Charge Conduction and Self-Breakdown in Transformer Oil
  Butcher, M.; Cevallos, M.; Neuber, A.; Krompholz, H.; Dickens, J.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):1143 - 1146
Abstract:  With a fast coaxial setup using a needle/plane geometry and a high sensitivity electrometer, conduction mechanisms in transformer oil at varying temperature and hydrostatic pressure are quantified. There are 3 stages in the conduction process prior to breakdown for highly nonuniform field geometries. Stage I is characterized by a resistive current at low fields. Stage II consists of a rapid rise in the injection current associated with increasing field due to a "tunneling" mechanism through the metal/dielectric interface. The transition from the resistive to tunneling stage occurs when the applied field reduces the barrier at the metal/insulator interface to a point where tunneling of charge carriers through the barrier begins. This transition point is polarity dependent. In stage III, at high fields the current reaches space charge saturation at electron mobilities >100 cm2/V*s prior to breakdown. The processes of final breakdown show distinct polarity dependence. Data for the negative needle exhibits strong pressure dependence of the breakdown voltage, which is reduced by 50% if the hydrostatic pressure is lowered from atmospheric pressure to hundreds of mtorr. Such a strong pressure dependence, at reduced hydrostatic pressure, indicates breakdown is gaseous in nature. This is supported by images of bubble/low density regions forming at the current injection point. Positive needle discharges show a reduction of only about 10% in breakdown voltage for the reduced pressure case. A 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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+ Limits of High Power Microwave Transmission due to Interface Breakdown
  A. Neuber, J. Krile, G. Edmiston, H. Krompholz, J. Dickens, "Limits of High Power Microwave Transmission due to Interface Breakdown," presented (oral) at 2005 Tri-Service VED Workshop, 12-16 September 2005
Abstract:  Not Available
+ Multi-Frequency and Multi-Mode Microwave Identification in a Vircator Research
  Xupeng Chen; Dickens, J.C.; Hatfield, L.L.; Mankowski, J.; Kristiansen, M.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):190 - 193
Abstract:  In virtual cathode oscillator (VIRCATOR) research, multi-frequency and multi-mode microwaves are coupled out and propagate along a waveguide. Identifying the microwave propagating modes has become a priority work for further research on microwave radiation physical mechanisms. Generally, an antenna matrix at the end of an open waveguide, which can shape the radiated microwave power distribution, is used to identify the microwave propagating modes [1-2]. Actual microwave radiation mechanisms in a VIRCATOR are complicated. Multi propagating modes and multifrequency microwaves coexist simultaneously, which challenges the antenna matrix method. In this paper, based on microwave propagating theory in a waveguide, a new method is proposed to identify multi-frequency and multi-mode microwaves, which is partially justified by the experimental data at Texas Tech University.

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+ Multistage Helical Flux Compression Generator Non-Explosive Test Bed
  Belt, D.; Dickens, J.; Mankowski, J.; Neuber, A.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):525 - 528
Abstract:  Helical Flux Compression Generators of small dimensions have been shown to produce energy output around 3 kJ into an inductive load. Adding a fuse opening switch has allowed us to produce 300kV into a 15 Ohm load. We are investigating inductive energy storage with emphasis on an electro-explosive fuse opening switch in order to improve upon previous results. We have designed and constructed a non-explosive test bed composed of two pulse forming networks (PFN). Each PFN provides a linear approximation during two different time ranges of the exponential rise response of a typical HFCG. This approach will be more cost and time effective than to drive the fuse with an explosive generator. Our initial goal will be to simulate a 15 kA HFCG unit followed by the simulation of a 50 kA HFCG.

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+ Shock Induced Conductivity for High Power Switching
  Veselka, H.; Neuber, A.; Dickens, J.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):734 - 737
Abstract:  Investigations of shock induced conductivity of insulators and semiconductors both crystalline and non-crystalline, were performed. Although the insulator-to-metallic state transition time was measured, the focus of this investigation was on the recovery phase of the induced conductivity (i.e. metallic-to-insulator state transition). The recovery time and shock conditions were measured with high speed electrical diagnostic equipment. The goal of this research is to determine the feasibility of using shock induced conductivity as a means of producing a high power opening switch. To minimize switch losses, the insulator-to-metallic transition time and conductance is also important, but has been more widely studied. Various shock profiles and intensities and used in the study. The shock is produced primarily with conventional commercial explosives. Shock reverberation is planed in some tests to minimize sample heating and to produce tailored shock time profiles. In addition, the impacts of sample thickness and compression duration on the induced conductivity were also studied.

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+ Similarities of Dielectric Surface Flashover at Atmospheric Conditions for Pulsed Unipolar and RF Excitation
  Krile, J.; Edmiston, G.; Neuber, A.; Dickens, J.; Krompholz, H.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):354 - 357
Abstract:  Mechanisms in vacuum flashover caused by rf (f<10 GHz) or unipolar voltages are virtually identical. Similarities between rf (representing high power microwave window breakdown on the high pressure side) and unipolar flashover are expected in an atmospheric environment as well. Our experimental setups enable studying both unipolar flashover and rf window flashover at atmospheric conditions while controlling excitation, temperature, pressure, humidity, and type of gas present. The local electric field at the flashover initiating points has been numerically calculated in detail for all test geometries. For both rf and unipolar pulsed excitation, the flashover dynamics are changed by the application of UV light to the dielectric surface. A UV pre-pulse has a distinct impact on the arc's path and a tendency to increase the hold-off electric field. The effect of humidity on the hold-off electric field for both pulsed unipolar and rf excitations, along with temporally resolved emission spectroscopy of the flashover event, will be discussed.

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+ Simulation Studies of Liquid Water Breakdown By a Sub-Microsecond Pulse
  Qian, J.; Joshi, R.P.; Kolb, J.; Schoenbach, K.H.; Dickens, J.; Neuber, A.; Cevallos, M.; Krompholz, H.; Schamiloglu, E.; Gaudet, J.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):738 - 741
Abstract:  An electrical breakdown model for liquids in response to a sub-microsecond (~ 100 ns) voltage pulse is presented, and quantitative evaluations carried out. It is proposed that breakdown is initiated by field emission at the interface of pre-existing micro-bubbles. Impact ionization within the micro-bubble gas then contributes to plasma development, with cathode injection having a delayed and secondary role. Continuous field emission at the streamer tip contributes to filament growth and propagation. This model can adequately explain almost all of the experimentally observed features, including dendritic structures and fluctuations in the pre-breakdown current. Two-dimensional, time-dependent simulations have been carried out based on a continuum model for water, though the results are quite general. Monte Carlo simulations provide the relevant transport parameters for our model. Our quantitative predictions match the available data quite well, including the breakdown delay times and observed optical emission. energy associated with a sub-microsecond pulse is too low to induce any significant heating [2]. Temperature increases of less than 6 K were predicted. Hence, bubble formation on the basis of localized liquid vaporization can effectively be ruled out. Here a general model of liquid breakdown is developed that incorporates two important features. First, the preexistence of spatially localized micro-bubbles, in equilibrium with the liquid phase, is implicitly assumed. As a result, no strong internal heating or vaporization is necessary for the creation of local low-density regions. Such bubbles are assumed to be filled with dissolved gas.

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+ The Impact of Electrode Material on the Pulsed Breakdown Strength of Water
  Wetz, D.; Mankowski, J.; Dickens, J.; Kristiansen, M.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):935 - 938
Abstract:  In the experiments presented here, various electrode materials were tested in an effort to determine the impact each has on increasing the dielectric strength of water. Prior investigations have tested materials such as stainless steel, copper, nickel, gold, silver, and cuprous oxide [1-4]. In our experiments, thin film coatings of various metallic alloys and oxides were applied to Bruce profiled stainless steel electrodes with an effective area of 5 cm2. An ion beam sputtering process was used to apply the coatings with thicknesses of several hundred nm. The electrodes were then tested across a water gap, with pulse lengths in both the microsecond and nanosecond time regimes. Electric fields in excess of 8 MV/cm were applied. Conclusions are made as to the impact electrode material has on the pulsed breakdown strength of water.

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Publication Year:  2004
+ Compact FCG Driven Inductive Energy Storage System
  J.-C. Hernandez, A. A. Neuber, M. Giesselmann, J. C. Dickens, and Magne Kristiansen, ”Compact FCG Driven Inductive Energy Storage System,” in Proceedings of MegaGauss X, Berlin, Germany, July 18 -23, p. 144-147, 2004,.
Abstract:  Not Available
+ Compact Pulsed Power
  M. Kristiansen, J. Dickens, H. Krompholz, M. Giesselmann, A. Neuber, J. Mankowski, L. Hatfield, “Compact Pulsed Power,“ Proceedings of the 5th International Symposium on Pulsed Power and Plasma Applications, Oct. 18-20, Chan-Won, Korea, p. 10-15, 2004. (Invited paper)
Abstract:  Not Available
+ Compact Pulsed Power
  M. Kristiansen, A. Neuber, J. Dickens, M. Giesselmann, and S. Shkuratov, “Compact Pulsed Power,“ MegaGauss X, Berlin, Germany, July 18 -23, p. 169-175, 2004. (Invited)
Abstract:  Not Available
+ DC and Pulsed Dielectric Surface Flashover at Atmsopheric Pressure
  J. T. Krile, A. Neuber, H. G. Krompholz, and J. C. Dickens, „DC and Pulsed Dielectric Surface Flashover at Atmsopheric Pressure,“ 2004 Power Modulator Conference, San Francisco, CA, 2004.
Abstract:  Not Available
+ Effect of temperature and pressure on DC pre-breakdown current in transformer oil
  Butcher, M.; Neuber, A.; Krompholz, H.; Dickens, J.; IEEE Conference Record - Abstracts. The 31st IEEE International Conference on Plasma Science, 2004. ICOPS 2004. 28 June-1 July 2004 Page(s):258
Abstract:  Summary form only given. Any attempt to model the complex interaction of hydrodynamic and electronic processes leading to breakdown in transformer oil suffers from the lack of microscopic transport data. Also, interface processes, such as electron emission from metal electrodes immersed in liquid, are poorly understood. As a first step toward the understanding of breakdown phenomenology, the voltage-current characteristics for pre-discharge conditions are measured. An experimental setup was constructed which allows temperature variations between 10/spl deg/C and 50/spl deg/C, at pressures between 0.5 and 3 bar. DC currents ranging from a few nA with a few kV of applied voltage, to a few /spl mu/A prior to full breakdown are measured using an electrometer. Preliminary results at NTP with a tip-plane geometry indicate Ohmic behavior at low voltages, Schottky emission at intermediate voltages, and saturation due to space charge at high voltages, and allow estimates on the physical parameters governing these effects. The indicated temperature range of the measurements is associated with a variation of the viscosity of a factor of 3, where we anticipate similar relative changes for the transport of electrons. The intermediate voltage range where a Schottky emission process is assumed will be emphasized. For instance, the electron mobility, derived from experimental data to about 0.06 cm/sup 2//Vs at NTP in the intermediate voltage range should distinctly vary with changing temperature and pressure.

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+ Electrical breakdown in transformer oil
  Cevallos, M.D.; Dickens, J.C.; Neuber, A.A.; Krompholz, H.G.; IEEE Conference Record - Abstracts. The 31st IEEE International Conference on Plasma Science, 2004. ICOPS 2004. 28 June-1 July 2004 Page(s):401
Abstract:  Summary form only given. The fundamental breakdown physics of transformer oils is investigated with high-speed electrical and optical diagnostics with temporal resolution down to 500 ps. Univolt 63 and Envirotemp FR3 (biodegradable) are used for this study. The system set up employs a cable discharge into a coaxial system with point/plane axial discharge and load line to providing a matched terminating impedance. Overall, the impedance of the system is matched at 50 ohms throughout with the exception of the very narrow gap region and includes a 50 ohm load resistor terminating the load line. Self breakdown is achieved by applying up to 50 kV to the charging line. Pulsed breakdown is achieved by charging a pulse forming line with a two way transient time of 300 ns, up to 100 kV. The pulse forming line is then fed into the discharge line via an oil spark gap. Transmission line type current sensors and a capacitive voltage divider with fast amplifiers/attenuators are used in order to attain a complete range of information from amplitudes of 0.1 mA to 1 kA with temporal resolutions of 300 ps. Optical measurements are performed on low level light emission using fast photo-multiplier tubes (risetime of 800 ps) spatially resolved, supplemented with high speed and spectroscopic investigations on a nanosecond timescale. Breakdown voltages at gap distances of 5 mm for pre, self, and pulsed breakdown voltages are given, where breakdown with negative needle tips show 20% higher breakdown voltages than the ones with positive needle. Velocities of propagating "tree"-structures for the pre and self-breakdown are a few km/s while pulsed breakdown velocities are several 10's of km/s, with higher velocities for a negative needle. The trees have to reach the opposite electrode before full breakdown occurs. Simultaneous optical measurements for a single breakdown event are presented, such as the luminosity in comparison to shadowgraphy images, which is necessary to describe the complex interaction of hydrodynamic phenomena (channel and tree formation and propagation) and charge carrier multiplication.

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+ High Power Microwave Breakdown of a Gas-Dielectric Interface at 90 to 760 Torr
  G. Edmiston, A. Neuber, H. Krompholz, J. Dickens, "High Power Microwave Breakdown of a Gas-Dielectric Interface at 90 to 760 Torr,” presented at the 46th Annual Meeting of the Division of Plasma Physics November 15-19, 2004, Savannah, GA, Meeting ID: DPP04APS
Abstract:  Not Available
+ Light-matter interaction in transformer oil
  Namihira, T.; Wang, D.; Neuber, A.; Butcher, M.; Dickens, J.; Krompholz, H.; IEEE Conference Record - Abstracts. The 31st IEEE International Conference on Plasma Science, 2004. ICOPS 2004. 28 June-1 July 2004 Page(s):448
Abstract:  Summary form only given. Considering highly stressed dielectric liquids, the role of mechanisms such as photoionization in the liquid volume or photoeffect at the cathode for the development of dielectric breakdown is investigated. We used a pulsed 300 W Xenon light source (25 mm output window, 5 degree divergence) with a broad spectral range of 200 to 1100 nm to study the impact of the light beam focused either solely on the high field region between the breakdown electrodes or including the electrodes. Typical field strengths in the electrode gap (/spl sim/4 mm gap, 3 mm tip radius,) were 15 to 25 kV/cm resulting in a DC current amplitude (without light) of up to 2 nA (apparatus resolution /spl sim/10 pA). Standard transformer oil, Univolt 61, and a biodegradable oil, Environtemp FR3 (natural ester fluid), were examined in the present work. Both oils exhibit strong optical absorption in the UV. However, Univolt 61 has its cut off wavelength at 450 nm, while bio oil easily transmits down to 350 nm. Below the cutoff wavelength, virtually all radiation is absorbed within a few mm. When pulsing the Xenon lamp at /spl sim/500 microsec no increase in DC current amplitude (increase <10 pA) could be detected for either oil. Increasing the pulse length to several seconds lead to a distinct increase in current amplitude (up to 300 pA), however, only for Univolt 61. Such an increase in current amplitude can also be achieved by raising the temperature of the dielectric liquid by external heating (/spl sim/100 pA/K). The temperature levels leading to similar current amplitudes due to heating by the Xenon lamp or external heating are comparable. Since bio oil absorbs only below 350 nm, the temperature rise due to the light irradiation was comparably smaller than in Univolt 61. Thus, any heating and increase in current were less pronounced in bio oil. For both oils, the observed behavior can be entirely explained by thermal effects. Both, photoionization and photoeffect have seemingly a minor impact on breakdown development. The detailed discussions are given in the present work.

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+ Modeling of Pulsed Radiating Structures
  "Modeling of Pulsed Radiating Structures", 2nd European Pulsed Power Symposium 2004, Hamburg, Germany, September 20-23, 2004 (with John Walter and J. Dickens).
Abstract:  Not Available
+ Nanosecond, optical diagnostics for liquid dielectric switches
  Kolb, J.F.; Xiao, S.; Goan, B.; Lu, X.P.; Schoenbach, K.H.; Laroussi, M.; Joshi, J.P.; Dickens, J.; Neuber, A.; Krompholz, H.; Cevallos, M.; Butcher, M.; IEEE Conference Record - Abstracts. The 31st IEEE International Conference on Plasma Science, 2004. ICOPS 2004. 28 June-1 July 2004 Page(s):402
Abstract:  Summary form only given. The high dielectric strength of liquid dielectrics allows for the design of small, low inductance and consequently fast high power switches. The investigation of the streamer formation which eventually leads to electrical breakdown requires diagnostic techniques with high temporal and spatial resolution. Optical methods, such as interferometry, Schlieren photography and shadowgraphy have been used to study the development of streamers and subsequent spark channel formation and decay in a pin-plane geometry. The temporal resolution is determined by the shutter speed of a high-speed camera, and was generally on the order of 1 ns. Interferometric measurements in water under high dielectric stress allowed for the characterization of the transient electric field distribution up to the imminent breakdown. Schlieren and shadow photographs allowed us to explore the development of the discharge and the switch recovery. With the pin electrode being the cathode tree-shaped inhomogeneities expand into the gap before breakdown is initiated by the formation of a single streamer that eventually bridges a gap of 400 /spl mu/m in about 7 ns. The recovery is determined by the formation of a vapor bubble that is cleared from the gap in about 1 ms. In oil, the processes involving the interaction of hydrodynamic and electronic processes are more complex. DC breakdown in a pin-plane geometry is strongly polarity dependent. Successively growing trees are observed, which bridge a 1-mm gap after as much as 1 /spl mu/s causing large breakdown delays. For fast pulse breakdown, the observed phenomena resemble more the ones observed in water. Gaining complete information on the breakdown phenomenology in oil requires the simultaneous use of all diagnostics methods including high resolution current measurements. Of special importance is information on the propagation of gaseous channels involved in the tree formation, and measurement of the correlated light emission indicating charge carrier amplification.

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+ Unipolar Surface Flashover
  J. Krile, A. Neuber, H. Krompholz, J. Dickens, "Unipolar Surface Flashover," presented at the 46th Annual Meeting of the Division of Plasma Physics November 15-19, 2004, Savannah, GA, Meeting ID: DPP04APS
Abstract:  Not Available
+ Voltage-current characteristic of transformer oil under high electrical stress
  Butcher, M.; Neuber, A.; Krompholz, H.; Dickens, J.; IEEE Conference Record - Abstracts. The 31st IEEE International Conference on Plasma Science, 2004. ICOPS 2004. 28 June-1 July 2004 Page(s):258
Abstract:  Summary form only given. The scattering cross-sections, transport coefficients, and details of the breakdown mechanism needed for describing current conduction in transformer oil at high applied voltages are virtually unknown. This makes it extremely difficult, if not impossible, to properly model electrical breakdown in oil. To address this issue, we have measured the V-I characteristic of transformer oil in the point-plane geometry for /spl sim/3 mm gap widths. Three regimes can be distinguished. (1) For low voltages, V <3 kV, the relationship between voltage and current is linear, exhibiting just resistive behavior within the measurement accuracy. (2) At intermediate voltages, the dependence is linear on a Fowler-Nordheim plot. (3) Between the breakdown voltage V/sub B/ /spl sim/ 30 kV and 10 kV, the current is proportional to V/sup 2/, indicating space charge limited current. Assuming a Schottky-type emission mechanism for electrons injected into the liquid, we derive an electron mobility of /spl sim/6.0/spl times/10/sup -6/ m/sup 2//Vs, which is close to values reported in the literature before. Assuming Fowler-Nordheim emission leads to 3.8/spl times/10/sup -6/ m/sup 2//Vs. The ion mobility is believed to be more than one order of magnitude lower. At this point, it is difficult to gain any more detailed information on charge transport and possible multiplication based on simple analytical methods. Hence, we applied our numerical modeling techniques already proven in analyzing high-field phenomena in polar liquids (e.g., water), to evaluate current conduction and the breakdown process in non-polar oil. By comparing our calculations with the experimental data, we hope to characterize important transport parameters, such as the electron ionization coefficient as a function of the electric field. We also present our attempts to extract details of the field-dependent non-linear processes and electrode effects close to the breakdown regime.

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Publication Year:  2003
+ Cavity resonance effect on a coaxial vircator
  Xupeng Chen; Dickens, J.; Eun Ha Choi; Mankowski, J.; Hatfield, L.L.; Kristiansen, M.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 2, 15-18 June 2003 Page(s):1165 - 1168 Vol.2
Abstract:  Traditionally, the radiated microwave frequency in a coaxial vircator is considered to be determined primarily by the virtual cathode oscillation frequency and the electron reflection frequency. However, some experiments at TTU show that the interaction between the virtual cathode oscillation and the cavity is a key in determining the microwave frequency and propagating mode. Particularly, we observe that the E-beam plays an important role in the cavity formation. Some possible explanations, including a virtual cavity concept, are proposed. The cavity resonance effect on a coaxial virtual cathode oscillator has been investigated in detail. The understanding of the E-beam characteristics is critical in optimizing the design of the cylindrical diode to avoid the microwave frequency shifting and mode competition.

[PDF]

+ Conductivity measurements of explosively shocked aluminum and OFHC copper used for armature material in a magnetic flux compression generator
  Hemmert, D.; Mankowski, J.; Rasty, J.; Neuber, A.; Dickens, J.; Kristiansen, M.; Digest of Technical Papers, PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 2, 15-18 June 2003 Page(s):1073 - 1076 Vol.2
Abstract:  Modeling and characterization of a magnetic flux compression generator (MFCG) requires detailed knowledge of the changes in conductivity of the MFCG materials during the shock-loading phase. In the studies reported here, a thin metallic strip is shocked with an explosively generated shock wave produced from a charge of composition C-4. The shock wave is intended to simulate the shock wave and pressures produced in MFCG research currently being conducted at Texas Tech University. These pressures are estimated to be between 1 and 3 GPa. The experimental setup is arranged so that the shapes of the metallic strip and shock front are the same, as confirmed using optical fibers. This was to ensure that the test sample was shocked uniformly. The metallic test strip is pulsed with a 70 A current pulse during application of the shock wave. The current and voltage across the test sample are measured directly to determine the change in conductivity. Pressure measurements are conducted in separate tests under similar conditions using strain gauges. The results are then compared to results determined previously using a split Hopkinson pressure bar apparatus (SHPB).

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+ Design criteria for prevention of armature "turn-skipping" in helical magnetic flux compression generators
  Rasty, J.; Le, X.; Dickens, J.; Neuber, A.; Kristiansen, M.; Pulsed Power Conference, 2003. Digest of Technical Papers. PPC-2003. 14th IEEE International Volume 2, 15-18 June 2003 Page(s):1077 - 1080 Vol.2
Abstract:  Helical magnetic flux compression generators (MFCGs) are capable of producing ultra-high power electric pulses by trapping and compressing a seed magnetic field into a load coil via an explosive-driven armature. The efficiency of helical MFCGs is generally very low, about 10%, due to large magnetic flux losses. One of the main sources of magnetic flux loss is the "turn-skipping" phenomenon, in which the expanding armature fails to establish contact with every turn of the helical coil, resulting in magnetic flux loss in the skipped turns of the coil. The "turn-skipping" phenomenon is related to non-uniform or asymmetric expansion of the armature, as well as detonation end effects. Equations describing the "turn skipping" phenomenon are developed in terms of the eccentricity of the armature with respect to the helical coil, the armature's wall thickness variations and the length of the detonation end effect. Design criteria for prevention of "turn-skipping" are presented in order to achieve optimum MFCG performance.

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+ Electrical Breakdown in Transformer Oil
  M. Cevallos, J. Dickens, A. Neuber H. Krompholz, “Electrical Breakdown in Transformer Oil,” Joint Fall Meeting of the Texas Sections of the APS and AAPT and Zone 13 Society of Physics Students, Lubbock, TX, Oct 2003 (abstract only published)
Abstract:  Not Available
+ Experimental results of a 2 GW vircator
  Mankowski, J.J.; Choi, E.H.; Dickens, J.C.; Xupeng Chen; Kristiansen, M.; IEEE Conference Record - Abstracts. The 30th International Conference on Plasma Science, 2003. ICOPS 2003. 2-5 June 2003 Page(s):187
Abstract:  Summary form only given. Experimental findings on the coaxial virtual cathode oscillator (vircator) at Texas Tech University are reported. Recent modifications to the system include extending the pulse forming line that now provides an applied diode voltage of 600 kV for 70 nanoseconds at 60 kA. Other modifications include diode voltage, current, and radiated field diagnostics. 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 2 GW corresponding to an efficiency of -6%. The mode observed at these high efficiencies is almost entirely TE/sub 11/. At lower efficiencies, both TM/sub 01/, and TE/sub 11/ modes are observed. These results suggest mode competition at lower efficiencies.

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+ Ferromagnetic and ferroelectric materials as seed sources for magnetic flux compressors
  Schoeneberg, N.; Walter, J.; Neuber, A.; Dickens, J.; Kristiansen, M.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 2, 15-18 June 2003 Page(s):1069 - 1072 Vol.2
Abstract:  permanent magnet based systems. Permanent magnets provide a larger energy-to-volume ratio given that the use of capacitors requires a power source as well as charging and firing circuitry. A recent design developed at Texas Tech University's Center for Pulsed Power and Power Electronics [S.I. Shkuratov, et al., 2002], focused on the demagnetization of a Neodymium-Iron-Boron magnet (Nd/sub 2/Fe/sub 14/B, B/sub r/= 1.23 T) by a shockwave generated from high explosives. The maximum specific energy achieved with this design was only 2.3 J/kg, which may not be sufficient for effectively seeding an FCG (fast capacitors have at least 20 J/kg). The same magnets were used with an alternative design, referred to as a strip FCG, which utilizes opposing magnets to generate initial magnetic field intensity within an air gap. The air gap exists between a central tube, filled with high explosives, and metal strips placed between the magnets a few millimeters off-axis. The detonation of the explosive causes the expansion of the central tube, subsequently compressing the flux into the strips and then into the load. The original strip FCG design [B.A. Bojko, et al., 1994] used oxide-barium magnets (B/sub r/= 0.2T), which produced an estimated specific energy of 5.27 J/kg into a low inductance load. These magnets were replaced with the Nd/sub 2/Fe/sub 14/B (B/sub r/= 1.23 T) magnets in order to achieve better performance, which will be analyzed with respect to the specific energy. In addition, a design utilizing a shocked ferroelectric material, PZT, as a seed current source is discussed. An explosively generated shock wave is passed through a ferroelectric material, generating a current that establishes the initial seed flux for an FCG. Preliminary tests of the ferroelectric sources indicate a possible theoretical specific energy of more than 11 J/kg or 25 J/dm/sup 3/. A comparison of the designs will be discussed with regard to the specific energy produced and the effectiveness of each to seed FCG's.

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+ Flashover Across a Dielectric Surface at Atmospheric Pressure
  J. Krile, A. Neuber, J. Dickens, and H. Krompholz, “Flashover Across a Dielectric Surface at Atmospheric Pressure,” Joint Fall Meeting of the Texas Sections of the APS and AAPT and Zone 13 Society of Physics Students, Lubbock, TX, Oct 2003 (abstract only published)
Abstract:  Not Available
+ Investigation of Pulse Power Thyristor Thermal Variations
  M. G. Hoffman, J. C. Dickens, and M. G. Giesselmann “Investigation of Pulse Power Thyristor Thermal Variations”, Proceedings of the 2003 IEEE Pulsed Power Conference, June 15-18, 2003 Dallas, Texas, p. 143…145.
Abstract:  Not Available
+ Nanosecond laser-triggered microwave switch
  McQuage, M.M.; Neuber, A.A.; Dickens, J.C.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 1, 15-18 June 2003 Page(s):309 - 312 Vol.1
Abstract:  The design and experimental testing of a laser-triggered microwave switch with a nanosecond activation time is described. The objectives of the project include, confirming that a nanosecond to subnanosecond risetime is achievable in the X-band waveguide at 9 GHz with the laser-triggered switch and to determine the minimum laser energy necessary to obtain the fastest possible risetime. A 1 kW pulsed X-band source with a 500 ns output pulse provides the microwave power for the system. A variable power Nd:YAG laser with a maximum 450 mJ at 532 nm, 10 ns FWHM output pulse is used in conjunction with an applied high voltage pulse to trigger the microwave switch. The microwave signal is switched with the rapid formation of plasma caused by the breakdown of a gas contained by a quartz tube inserted through a section of waveguide. The centerpiece of the waveguide system is a magic tee, which controls the direction of power flow through the system. Compared to tests in air and N/sub 2/, the best results have been obtained in argon. Risetimes below 2 ns have been obtained using argon at a reduced pressure of 150 Torr and a high voltage pulse of 28 kV from a spark gap. The impact of gas pressure, applied voltage pulse and applied laser pulse on the risetime of the microwave switch are discussed.

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+ Optical diagnostics of liquid nitrogen volume pre-breakdown events
  Butcher, M.; Neuber, A.; Krompholz, H.; Dickens, J.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 2, 15-18 June 2003 Page(s):1029 - 1032 Vol.2
Abstract:  An increased need for compact pulsed power systems requiring new switching technologies combined with the benefits of cryogenic properties, such as higher energy density and miniaturization, has lead to increased interest in liquid nitrogen as a switching medium. High hold off voltage, low dielectric constant, and low environmental impact are further advantages of liquid nitrogen. Characterization of breakdown is investigated using high-speed (temporal resolution < 1 ns) optical and electrical diagnostics in a coaxial system with 52 /spl Omega/ impedance. Experiments are done in self-breakdown mode in super-cooled liquid nitrogen with a temperature near 70 K. Discharge current and voltage are determined using transmission line type current sensors and capacitive voltage dividers. Discharge luminosity is measured with photomultiplier tubes (risetime/spl ap/800 ps) that are focused on the negative electrode tips and the center of the channel. Optical investigations of breakdown and pre-breakdown events on a nanosecond time scale will provide a better understanding of the fundamental physics of breakdown formation. Detailed optical and spectroscopic diagnostics combined with high-speed electrical diagnostics are aimed at clarifying the overall breakdown mechanisms, including electronic initiation and bubble formation. The breakdown initiation/development will be discussed.

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+ Phenomenology of conduction and breakdown in transformer oil
  Butcher, M.; Cevallos, M.; Haustein, M.; Neuber, A.; Dickens, J.; Krompholz, H.; Electrical Insulation and Dielectric Phenomena, 2003. Annual Report. Conference on 2003 Page(s):301 - 304
Abstract:  In a coaxial test apparatus enabling the measurement of voltage and current at the test gap, dc conduction and breakdown in transformer oil caused by the application of dc voltages are investigated. Current measurements cover the range from 10/sup -1/ A to 1 kA, with temporal resolutions of milliseconds at the lowest current amplitudes to sub-nanoseconds for currents larger than 10/sup -4/ A. The dc current/voltage characteristic for sub-breakdown voltage amplitudes point to the injection of charge carriers, allow us to characterize the transport mechanisms, and the influence of space charges. For voltages approaching breakdown thresholds, quasi dc-currents rising from nanoamperes to microamperes are superimposed by current pulses with amplitudes of milliamperes and above, and durations of nanoseconds. The onset of these current pulses occurs up to 10 /spl mu/s before breakdown. One of these current pulses reaches a critical amplitude causing voltage breakdown and current rise to the impedance-limited value within 2 ns. Additional optical diagnostics using photomultipliers and high-speed photography with gated microchannel plates yield information on hydrodynamic processes and charge carrier amplification mechanisms associated with the current pulses and final breakdown, such as bubble formation, as well as on the development of the spark plasma finally bridging the gap.

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+ Physical efficiency limits of inch-sized helical MFCGs
  Neuber, A.A.; Hernandez, J.-C.; Holt, T.A.; Dickens, J.C.; Kristiansen, M.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 1, 15-18 June 2003 Page(s):413 - 416 Vol.1
Abstract:  Helical magnetic flux compression generators (MFCG) are attractive energy sources with respect to their specific energy output. A variety of one-time use applications would benefit from small inch-sized helical generators with high specific energy output. However, it is widely accepted that the generator performance deteriorates with decreasing size. Previous experimental data have shown that the increase of the ohmic resistance of the MFCG with a reduction in size is the primary cause for the observed behavior when the initial generator inductance is held constant. We will analyze the situation in more depth and quantify how much the efficiency is determined by ohmic losses and intrinsic flux losses (flux that is left behind in the conductors and lost for compression) for different generator sizes and geometries. Our simple constant diameter MFCGs exhibit more intrinsic than ohmic losses (69% compared to 16%), while our MFCGs with tapered armatures display less intrinsic and more ohmic flux losses (13% compared to 66%), however, at increased overall efficiency. We will show experimental and calculated data and discuss the physical efficiency limits and scaling of generator performance at small sizes.

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+ Physics of dielectric surface flashover at atmospheric pressure
  Krile, J.; Neuber, A.; Dickens, J.; Krompholz, H.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 1, 15-18 June 2003 Page(s):285 - 288 Vol.1
Abstract:  The limits of the applicability of DC, AC, or pulsed high voltage are determined by breakdown along insulators or insulating support structures. It is of major technical importance to predict breakdown voltages for given structures, with parameters such as geometry, material, and temporal characteristics of the applied voltage. The impact of atmospheric conditions such as humidity, pressure, temperature, and types of gas present is also important. A setup has been devised to simulate and closely monitor flashover across various gap distances and insulator geometries at atmospheric conditions at different humidities. Current, voltage, luminosity, and optical emission spectra were measured with nanosecond to subnanosecond resolution. Spatially and temporally resolved light emission data yielded quantitative information about the charge carrier amplification, the location of this amplification, and its role in the formation of streamers.

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+ Prebreakdown current behavior in DC volume breakdown in transformer oil
  Butcher, M.; Neuber, A.; Krompholz, H.; Dickens, J.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 1, 15-18 June 2003 Page(s):289 - 292 Vol.1
Abstract:  The phenomenology of prebreakdown events in transformer oil is investigated using high-speed electrical and optical diagnostics. Data collection using a coaxial test setup terminating into a 50/spl Omega/ load line to simulate a matched impedance system allows very fast risetimes. Transmission line type current sensors and capacitive voltage dividers with temporal resolution of 300 ps provide information about the discharge voltage and current. Steady, DC currents ranging from a few nA with less than 10 kV of applied voltage, to a few /spl mu/A prior to full breakdown are measured using an electrometer. Prebreakdown events are measured with positive and negative charging voltages with respect to ground. Light emission from the discharge is measured using a series of fast photomultiplier tubes, (risetimes 800 ps), that observe positive and negative electrode tips and center of the channel. Preliminary results on self-breakdown (breakdown voltage +44 kV) with a 2.35 mm gap show a DC (seed) current of several hundred nA with prebreakdown spikes of a few mA immediately before final breakdown. Periodicity of the current spikes combined with a general increase in magnitude prior to full breakdown has been observed. Data collection using a negative charging line, with respect to ground with enhanced field at the cathode, indicates current spikes that are typically 25 to 50% faster than spikes using a positive charging line with enhanced field at the anode. Detailed optical diagnostics along with high-speed electrical diagnostics of the pre-breakdown phase will address the physical mechanisms initiating volume breakdown.

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+ Pulsed and self electrical breakdown in biodegradable oil
  Cevallos, M.D.; Dickens, J.C.; Neuber, A.A.; Haustein, M.A.; Krompholz, H.G.; 2003. ICOPS 2003. IEEE Conference Record - Abstracts. The 30th International Conference on Plasma Science, 2-5 June 2003 Page(s):315
Abstract:  The fundamental breakdown physics of biodegradable oil is investigated with a set up that employs a cable discharge into a coaxial system with axial discharge and load line to simulate a matched terminating impedance. No discontinuities are created in the system lines when entering the discharge chamber with the implementation of a unique feed-through design. The entire impedance of the system is matched at 50 ohms. A novel design for impedance matching transitions from the discharge cable to the coaxial system to the load line allow for a sub-nanosecond response. Final results are measured on pulsed and self breakdown voltages of up to 200 kV. Self breakdown is achieved by charging the discharge cable and load line to +/- 100 kV respectively. Pulsed breakdown is achieved by charging the discharge cable and load line to +100 kV. Shorting the discharge cable generates a reflected negatively polarized pulse causing breakdown. High speed electrical and optical diagnostics have temporal resolution down to several 100 ps A complete range of information from amplitudes of 0.1 mA to 1 kA with temporal resolutions of 300 ps is achieved by using transmission line type current sensors with fast amplifiers. Capacitive voltage dividers with fast attenuators are also used. Optical measurements are performed on low level light emission using spatially resolved, fast photo-multiplier tubes (risetime of 800 ps), supplemented with high speed photography and spectroscopic investigations on a nanosecond timescale Detailed optical and spectroscopic diagnostic along with high speed electrical diagnostics will address the mechanism initiating/assisting biodegradable oil volume breakdown.

[PDF]

+ Reflex-triode geometry of the virtual-cathode oscillator
  Lara, M.B.; Mankowski, J.; Dickens, J.; Kristiansen, M.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 2, 15-18 June 2003 Page(s):1161 - 1164 Vol.2
Abstract:  An eight-stage four-hundred kilovolt Marx bank, in connection with a 60 nanosecond pulse-forming line, is constructed and utilized as a pulsed source to power a planar version of the virtual cathode oscillator (vircator). Eight .1/spl mu/F capacitors, charged to 50 kV each, are switched in series by dry-air pressurized spark gaps. The energy from the bank charges a 23 ohm oil transmission line, breaking a peaking gap when the maximum voltage is reached, delivering a 60 ns-300 kV pulse to the diode. The design of the planar or reflex-triode geometry vircator is based upon claims of high efficiency by Didenko et al. A previously constructed TTU vircator includes a unique E-beam source, the brush cathode; in which a circular array of pins is used as an explosive field emission source to produce relatively high beam currents. The anode consists of a round wire mesh through which the E-beam passes, generating a dense cloud of negative charge known as a virtual cathode. This initial phase of testing is composed of basic operation of the entire system and baseline output power and efficiency measurements.

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+ Self electrical breakdown in biodegradable oil
  Cevallos, M.D.; Dickens, J.C.; Neuber, A.A.; Haustein, M.A.; Krompholz, H.G.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 2, 15-18 June 2003 Page(s):1036 - 1039 Vol.2
Abstract:  The fundamental breakdown physics of biodegradable oil is investigated with high-speed electrical and optical diagnostics with temporal resolution down to several 100 ps. The set up employs a cable discharge into a coaxial system with axial discharge and load line to simulate matched terminating impedance. A unique feed-through design creates no discontinuities in the system lines through the discharge chamber. The impedance of the system is matched at 50 ohms including a novel design for impedance matching transitions from discharge cable to coaxial system to load line allowing for a sub-nanosecond response. This paper presents results on self-breakdown with voltages of up to 60 kV. Self-breakdown is achieved by charging the discharge cable and load line to +/-30 kV respectively. Transmission line type current sensors and a capacitive voltage divider with fast amplifiers/attenuators are used in order to obtain a complete range of information from amplitudes of 0.1 mA to 1 kA with temporal resolutions of 300 ps. Optical measurements include high speed photography and shadowgraphy. Detailed optical diagnostics along with high-speed electrical diagnostics will address the mechanism initiating/assisting biodegradable oil volume breakdown.

[PDF]

+ Short pulse electric field sterilization of liquid media
  Wetz, D.; Truman, K.; Dickens, J.; Mankowski, J.; Neuber, A.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 2, 15-18 June 2003 Page(s):1124 - 1127 Vol.2
Abstract:  In recent years, researchers have investigated methods of liquid sterilization by applying pulsed high electric fields with some degree of success. The mechanism by which microorganisms are damaged has been shown to be a function of the local electric field and exposure time while independent from thermal and electrolytic effects from the applied pulse. Most published experiments have employed electrical pulses of 10's of kV and microsecond long pulse lengths. We are employing electrical pulses in the 100's of kV range with 100 nanosecond long pulse lengths. This type pulse should be more effective at killing microorganisms and minimize energy losses due to thermal processes in the liquid media.

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+ Single-Shot and Overstressing of High Voltage Capacitors for Compact Arkadiev-Marx Genertor
  "Single-Shot and Overstressing of High Voltage Capacitors for Compact Arkadiev-Marx Genertor", Proc.14th IEEE International Pulsed Power Conference, Dallas, TX, June 16-19, 2003 p. 723 (with S. Shkuratov, E. Talantsev, and J. Dickens).
Abstract:  Not Available
+ Small sized MFCG for driving a high impedance load
  Hernandez, J.-C.; Neuber, A.A.; Dickens, J.C.; Kristiansen, M.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 2, 15-18 June 2003 Page(s):1065 - 1068 Vol.2
Abstract:  End-initiated small volume magnetic flux compression generators (MFCG) have at least one order of magnitude higher energy density (by weight or volume) than capacitive energy storage with similar discharge time characteristics. Since the prime energy is built into the MFCG in form of HE, the capacitor looses even more ground if the necessary prime energy source and the charging supply are included in the weight/volume balance. However, simple MFCGs with a single helix produce high output energy only into low inductance loads, thus producing several 100 kA of current at a voltage level of only a few 10 kV. Many pulsed power devices require less current but a considerably higher voltage level. Two approaches for achieving a higher output voltage level, both utilizing two staged MFCGs, have been reported in the open literature. The first employs a more traditional transformer coupling; the second relies on a dynamic transformer or flux-trapping scheme. Although the traditional transformer coupling has theoretically the better efficiency, we chose the latter approach for our generator design, mostly since it requires a smaller number of components. Our generator has a total length of 250 mm, a helix inner diameter of 51 mm, and is wound with Teflon insulated stranded wire of different sizes in the range from AWG 12 to AWG 22. We have presently achieved an energy gain of /spl sim/ 8 and will discuss the generator performance based on experimental current/voltage waveforms.

[PDF]

+ Space Charge Limited Current for a 1-D Cylindrical Diode
  "Space Charge Limited Current for a 1-D Cylindrical Diode", Proc. 14th IEEE International Pulsed Power Conference, Dallas, TX, June 16-19, 2003 p. 467 (with X. Chen, J. Dickens, E. Choi).
Abstract:  Not Available
+ Surface flashover across ceramic disks in vacuum at cryogenic temperatures
  Keene, H.; Dickens, J.; Neuber, A.; Krompholz, H.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 1, 15-18 June 2003 Page(s):305 - 308 Vol.1
Abstract:  As superconducting technology becomes more viable in the marketplace, especially in high power applications, the need for a well researched high thermal conductivity electrical insulator is needed. The electrical failure mode for these types of insulators is often surface flashover at subatmospheric temperature and pressure. Testing of two such insulators, aluminum nitride and aluminum oxide, for this failure mode is done for two differing electrode geometries. In addition three coats of GE 7031 dielectric varnish are applied to the exposed parts of the insulator for comparison testing with nonvarnished samples. In general the testing shows an increasing breakdown voltage trend with decreasing temperature. These results indicate a temperature related dependence of the secondary electron emission and electron induced outgassing, which is a component in the process of surface flashover. The addition of the varnish results in a lowered breakdown voltage. The research also covers the effect of electrode conditioning, and presents optical diagnostics of the gas species involved during breakdown.

[PDF]

Publication Year:  2002
+ All-Explosive Pulsed Power Generator System
  A. Neuber, S. Shkuratov, E. Talantsev, J. Walter, T. Holt, J. Dickens, and M. Kristiansen, “All-Explosive Pulsed Power Generator System,” at the Ninth International Conference on Megagauss Magnetic Field Generation and Related Topics, Moscow – St. Petersburg, July 7-14, 2002.
Abstract:  Not Available
+ Dependence of Flux Losses on MCG Helix Geometry
  A. Neuber, T. Holt, J. Hernandez, J. Dickens, and M. Kristiansen, “Dependence of Flux Losses on MCG Helix Geometry,” presented at the 14th International Conference on High-Power Particle Beams, Albuquerque, NM, June 23 - 28, 2002.
Abstract:  Not Available
+ Electric breakdown in liquid nitrogen
  Krompholz, H.; Neuber, A.; Haustein, M.; Dickens, J.; Proceedings of 2002 IEEE 14th International Conference on Dielectric Liquids, 2002. ICDL 2002. 7-12 July 2002 Page(s):167 - 170
Abstract:  The phenomenology of breakdown in liquid nitrogen is investigated with high-speed electrical and optical diagnostics (temporal resolution down to several 100 ps). The discharge apparatus uses a cable discharge into a coaxial system with axial discharge, and a load line to simulate a matched terminating impedance. Main experiments are done in self-breakdown mode in supercooled liquid nitrogen. Transmission line type current sensors and capacitive voltage dividers with fast amplifiers/attenuators cover an amplitude range of 0.1 mA to 1 kA with a time resolution of 300 ps, providing complete information about discharge voltage and current. The light emission is measured with fast photomultiplier tubes (risetime 800 ps), and these optical measurements will be supplemented by high-speed photography and spectroscopic investigations on a nanosecond time scale. First results on self-breakdown with a gap width of 1 mm and electrodes with 5 mm radius of curvature (breakdown voltage 42 kV) show a three-phase development: the current rises from an unknown level to several mA during 2 ns, stays approximately constant for 100 ns with superimposed ns-duration spikes, and shows a final exponential rise to the full impedance limited current amplitude during several nanoseconds. Detailed optical and spectroscopic diagnostics along with the high-speed electrical diagnostics will in particular address the physical mechanisms initiating/assisting the liquid nitrogen volume breakdown, such as bubble formation during the pre-breakdown phase.

[PDF]

+ Explosive-Driven Generation of Transient Antennas
  A. Neuber, N. Schoeneberg, J. Dickens, and M. Kristiansen, “Explosive-Driven Generation of Transient Antennas,” presented at the Ninth International Conference on Megagauss Magnetic Field Generation and Related Topics, Moscow – St. Petersburg, July 7-14, 2002.
Abstract:  Not Available
+ Fast dielectric volume breakdown in liquid nitrogen
  Neuber, A.; Krompholz, H.; Haustein, M.; Dickens, J.; IEEE Conference Record - Abstracts. The 29th IEEE International Conference on Plasma Science, 2002. ICOPS 2002. 26-30 May 2002 Page(s):196
Abstract:  Summary form only given, as follows. Miniaturization of electrical components along with growing superconductor technology requires a better understanding of the phenomenology of breakdown in liquid nitrogen. It is known that the time delay between breakdown-onset and final impedance-limited arc current can occur within a few nanoseconds. For a temporal resolution down to several 100 ps, a discharge apparatus was built and tested that uses a cable discharge into a coaxial system with axial discharge, and a load line to simulate a matched terminating impedance. Main experiments are done in self-breakdown mode in supercooled liquid nitrogen, pulsed breakdown at high over-voltages in standard electrode geometry is investigated as well. Transmission line type current sensors and capacitive voltage dividers with fast amplifiers/attenuators cover an amplitude range of 0.1 mA to 1 kA with a time resolution of 300 ps, providing complete information about discharge voltage and current. The light emission is measured with fast photomultiplier tubes (risetime 800 ps), and these optical measurements will be supplemented by high-speed photography and spectroscopic investigations on a nanosecond time scale. Preliminary results on self-breakdown in the surface flashover mode with a gap width of 2 mm and electrodes with 5 mm radius of curvature (breakdown voltage /spl sim/ 60 kV) show a three-phase development: the current rises from an unknown level to several mA during 2 ns, stays approximately constant for 100 ns with superimposed ns-duration spikes, and shows a final exponential rise to the full impedance limited current amplitude during several nanoseconds. The detailed optical and spectroscopic diagnostics along with the high-speed electrical diagnostics will in particular address the physical mechanisms initiating/assisting the liquid nitrogen volume breakdown, such as bubble formation during the pre-breakdown phase.

[PDF]

+ Feasibility study of an explosively formed transient antenna
  Neuber, A.; Schoeneberg, N.; Dickens, J.; Kristiansen, M.; Conference Record of the Twenty-Fifth International Power Modulator Symposium, 2002 and 2002 High-Voltage Workshop. 30 June-3 July 2002 Page(s):374 - 377
Abstract:  The feasibility of utilizing the chemical energy stored in high explosives to generate an antenna capable of radiating for several microseconds is studied. Crucial parameters such as conductivity as a function of time, maximum achievable antenna length for given initial device volume and weight, and material dependence are assessed by sub microsecond optical and electrical diagnostics. By utilizing a rotating framing mirror camera with up to 4 Megaframes per second, which produces a color image sequence consisting of 125 frames, possible premature breakup of the transient antenna rod is measured with adequate spatial and temporal resolution, thus revealing a rod growth velocity of a few millimeters/microsecond. Electrical diagnostic, primarily aimed at the conductivity between selected points along the rod propagation, enables to make a connection with the observed behavior based on the optical diagnostics. Maintaining electrical contact at the base of the device while the rod is fully formed is crucial and will be discussed in detail.

[PDF]

+ Geometry Impact on Flux Losses in MFCGs
  A. Neuber, T. Holt, J. Hernandez, J. Dickens, and M. Kristiansen, “Geometry Impact on Flux Losses in MFCGs,” presented at the Ninth International Conference on Megagauss Magnetic Field Generation and Related Topics, Moscow – St. Petersburg, July 7-14, 2002.
Abstract:  Not Available
+ High Voltage, Sub Nanosecond Feedthrough Design for Liquid Breakdown Studies
  M. Cevallos, J. Dickens, A. Neuber, H. Krompholz, “High Voltage, Sub Nanosecond Feedthrough Design for Liquid Breakdown Studies,” presented at the 14th International Conference on High-Power Particle Beams, Albuquerque, NM, June 23 - 28, 2002, AIP conference Proceedings, Vol. 650, p. 73-76.
Abstract:  Experiments in self-breakdown mode and pulsed breakdown at high over-voltages in standard electrode geometries are performed for liquids to gain a better understanding of their fundamental breakdown physics. Different liquids of interest include liquids such as super-cooled liquid nitrogen, oils, glycerols and water. A typical setup employs a discharge chamber with a cable discharge into a coaxial system with axial discharge, and a load line to simulate a matched terminating impedance, thus providing a sub-nanosecond response. This study is focused on the feed-through design of the coaxial cable into this type of discharge chamber, with the feed-through being the critical element with respect to maximum hold-off voltage. Diverse feedthroughs were designed and simulated using Maxwell 3-D Field Simulator Version 5. Several geometrically shaped feed-through transitions were simulated, including linearly and exponentially tapered, to minimize electrostatic fields, thus ensuring that the discharge occurs in the volume of interest and not between the inner and outer conductor at the transition from the insulation of the coaxial cable to the liquid. All feedthroughs are designed to match the incoming impedance of the coaxial cable. The size of the feedthroughs will vary from liquid to liquid in order to match the coaxial cable impedance of 50. The discharge chamber has two main ports where the feed-through will enter the chamber. Each feed-through is built through a flange that covers the two main ports. This allows the use of the same discharge chamber for various liquids by changing the flanges on the main ports to match the particular liquid. The feedthroughs were designed and built to withstand voltages of up to 200 kV. The feedthroughs are also fitted with transmission line type current sensors and capacitive voltage dividers with fast amplifiers/attenuators in order to attain a complete range of information from amplitudes of 0.1mA to 1 kA with a temporal resolution of 300 ps. ©2002 American Institute of Physics

[PDF]

+ Liquid Nitrogen As Fast High Voltage Switching Medium
  J. Dickens, A. Neuber, M. Haustein, H. Krompholz, “Liquid Nitrogen As Fast High Voltage Switching Medium,” presented at the 14th International Conference on High-Power Particle Beams, Albuquerque, NM, June 23 - 28, 2002, AIP conference Proceedings, Vol. 650, p. 95-98.
Abstract:  Not Available
+ Microwave breakdown studies of He-N² mixtures in a pillbox cavity from 760 to 3040 torr
  Hemmert, D.; Neuber, A.; Dickens, J.; Conference Record of the Twenty-Fifth International Power Modulator Symposium, 2002 and 2002 High-Voltage Workshop. 30 June-3 July 2002 Page(s):232 - 235
Abstract:  Microwave breakdown of various He-N/sub 2/ mixture combinations is investigated utilizing an S-band double window pillbox cavity. The objective is to determine the best combination of the two gases to maximize the mixture's ability to cool a dielectric surface while maintaining high breakdown thresholds. Helium is known to be an excellent source to dissipate heat from a dielectric, but it also has a low microwave breakdown threshold. Nitrogen does not transport heat as well, but has a much higher breakdown threshold. The studies focused on generating a series of E-field vs pressure curves for breakdown to help identify optimum He-N/sub 2/ mixture ratios. The S-band double window pillbox has a 333 cm/sup 3/ cavity with two ports to flow the gas mixture through. The pillbox is placed in a traveling wave resonant ring (TWRR) coupled to a 2.85 GHz, 4 MW, magnetron. This combination of double window pillbox and TWRR allows for testing power levels up to 40 MW. High speed diagnostics are used to measure the incident/reflected power and discharge luminosity. Coupled mass flow controllers maintain the gas mixture ratio and continuous gas flow through the cavity. Investigations can be conducted with single or multiple pulsed operations. Results ranged from a minimum of 5 MW for pure helium at 760 torr, to greater than 40 MW for pure nitrogen at 3040 torr.

[PDF]

+ Surface Flashover Across Ceramic Disks in Vacuum at Cryogenic Temperatures
  Keene, H.; Dickens, J.; Neuber, A.; Conference Record of the Twenty-Fifth International Power Modulator Symposium, 2002 and 2002 High-Voltage Workshop. 30 June-3 July 2002 Page(s):293 - 296
Abstract:  Not Available
Publication Year:  2001
+ Calculation of air temperature and pressure history during the operation of a flux compression generator
  Xiaobin Le; Rasty, J.; Neuber, A.; Dickens, J.; Kristiansen, M.; Pulsed Power Plasma Science, 2001. PPPS-2001. Digest of Technical Papers Volume 2, 17-22 June 2001 Page(s):939 - 942 vol.2
Abstract:  During the operation of magnetic flux compression generators (MFCG), the gas-plasma, shocked by the rapidly expanding armature, could lead to electrical arcing across the gas between the armature and the stator at locations where physical contact between the armature and stator has not yet occurred. This will result in a loss of magnetic flux and a decrease in the electrical efficiency of the MFCG. Therefore, knowledge of the ensuing gas temperature and pressure histories is necessary for identification of loss mechanisms in an effort to optimize the efficiency of MFCGs. This paper describes the procedure for estimating the air temperature and pressure histories via finite element (FE) simulation of the armature expansion and its ensuing contact with the stator in an MFCG. First, the validity of the FE model was verified by comparing deformation contours obtained from the simulations to those obtained experimentally via high-speed photography. Utilizing the pressure history data obtained from the FE results, the air temperature was theoretically calculated. The results indicate that the air pressure and temperature in an MFCG, having a compression ratio of 1.8, could be as high as 30 MPa and 4000/spl deg/ Kelvin, respectively.

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+ Compact explosive driven shock wave ferromagnetic generators
  Shkuratov, S.I.; Talantsev, E.F.; Kristiansen, M.; Dickens, J.; Hernandez, J.C.; Neuber, A.; Digest of Technical Papers, Pulsed Power Plasma Science, 2001. PPPS-2001. Volume 1, 17-22 June 2001 Page(s):158 - 161 vol.1
Abstract:  The results are presented of tests with compact, explosively driven shock wave ferromagnetic generators. The shock wave from a high explosive charge is passed along the axis of a cylindrical, hard magnet. Two types of permanent magnets were used in the experiments: rare-earth NdFeB cylinders (D = 2.5 cm, L = 1.9 cm) and hard ferrite BaFe/sub 2/O/sub 3/ cylinders (D = 2.2 cm, L = 2.5 cm). The shock wave demagnetizes the cylinder, reducing the flux from the remnant value to zero. This change in flux generates a voltage in the winding. The current generated in the loads of the generators yielded a peak of 0.75 kA. The operation of the shock wave ferromagnetic generators was analyzed by the Maxwell 3D code. An analysis is given on the specific features of pulse generation in a system like this.

[PDF]

+ Conductivity measurements of MFCG armature material under shock and high strain rates utilizing a split-hopkinson pressure bar apparatus
  Hemmert, D.; Rasty, J.; Neuber, A.; Dickens, J.; Le, X.; Kristiansen, M.; Digest of Technical Papers, 2001 Pulsed Power Plasma Science, PPPS-2001. Volume 1, 17-22 June 2001 Page(s):265 - 268
Abstract:  Not Available
+ Effect of Electron-Beam Pulse Length on Microwave Efficiency of Coaxial Vircator
  "Effect of Electron-Beam Pulse Length on Microwave Efficiency of Coaxial Vircator", Proc. 13th IEEE International Pulsed Power Conference and the 28th IEEE Conference on Plasma Science, Las Vegas, NV, June 17-22, 2001 (with W. Jiang, K. Woolverton, and J. Dickens).
Abstract:  Not Available
+ Experimental and numerical investigation of armature/stator contact in magnetic flux compression generators
  Rasty, J.; Xiaobin Le; Neuber, A.; Dickens, J.; Kristiansen, M.; Digest of Technical Papers, Pulsed Power Plasma Science, 2001. PPPS-2001. Volume 1, 17-22 June 2001 Page(s):106 - 109 vol.1
Abstract:  The efficiency of a magnetic flux compression generators (MFCG) is highly dependent on the expanding characteristics of the exploding armature and the nature of contact between the armature and the surrounding stator coil. A hydrodynamic finite element (FE) model was developed to simulate the expansion characteristics of the armature and its ensuing impact with the stator. The effectiveness of the FE model to simulate the explosive behavior of the armature was qualified by comparing the numerical results with experimentally measured parameters. Specifically, the radial displacement of the armature as well as the axial velocity of the armature/stator contact point were measured experimentally and compared with numerical results showing excellent agreement between the two. The results indicated that the radial and axial velocity with which the armature impacted the stator did not change through the length of the armature. However, the results showed that the velocity with which the contact point between the armature and the stator traveled along the length of the armature decreased as the explosion process went on. As expected, the axial propagation velocity of the contact point was found to be at its highest value (2.25 X detonation velocity) at the region close to the detonation end while approaching the detonation velocity at points away from the detonation end.

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+ Experimental study of compact explosive driven shock wave ferroelectric generators
  Shkuratov, S.I.; Kristiansen, M.; Dickens, J.; Neuber, A.; Altgilbers, L.L.; Tracy, P.T.; Tkach, Y.; Digest of Technical Papers, Pulsed Power Plasma Science, 2001. PPPS-2001. Volume 2, 17-22 June 2001 Page(s):959 - 962 vol.2
Abstract:  The design of explosive driven ferroelectric generators is presented and experimental data are discussed. The active elements are lead zirconium titanate (PZT) disks with diameter D=25 mm and thicknesses H=2.5 mm and H=6 mm and PZT cylinders with D=21 mm and H=25 mm. The high explosive charge was varied from 4.2 g to 30 g. Two different ways to initiate shock waves in the active elements were used: explosively driven flyer plates and direct action of high explosives. The data presented is for the maximum power into a resistive load.

[PDF]

+ Experimental study of compact explosive-driven shock wave ferroelectric generators
  Shkuratov, S.; Kristiansen, M.; Dickens, J.; Neuber, A.; Altgilbers, L.L.; Tracy, P.T.; Tkach, Y.; IEEE Conference Record - Abstracts. Pulsed Power Plasma Science, 2001.17-22 June 2001 Page(s):227
Abstract:  Summary form only given. The design of shock wave ferroelectric generators driven by high explosives is presented and experimental data are discussed. The active elements are lead zirconium titanate (PZT) disks with diameter D=25 mm and thickness L=2.5 mm, and PZT cylinders with D=21 mm and L=25 mm. The high explosive charge was varied from 4.2 g to 30 g. Two different ways to initiate shock waves in the active elements were used: explosively driven flyer plates and direct action of high explosives. The data are presented on the maximum power released in the resistive load and on the effect of the load inductance and the load capacitance on the amplitude of the pulse produced. The experimental results are discussed in comparison to numerical simulation with the commercial circuit simulator PSPICE. An analysis is given of the specific features of pulse generation in a system like this

[PDF]

+ Explosive-Driven Moving Magnet Generators
  "Explosive-Driven Moving Magnet Generators", Proceedings of 13th IEEE International Pulsed Power Conference, Las Vegas, Nevada, June 2001, p. 227 (with S.I. Shkuratov, M. Kristiansen, and J.C. Dickens).
Abstract:  Not Available
+ High Voltage Testing of Capacitors
  "High Voltage Testing of Capacitors", Proceedings of 13th IEEE International Pulsed Power Conference, Las Vegas, Nevada, June 2001, p. 1563 (with S.I. Shkuratov, J.C. Dickens and E. Horrocks).
Abstract:  Not Available
+ Impact of helix geometry on MCG flux losses [magneto cumulative generators]
  Holt, T.; Neuber, A.; Dickens, J.; Kristiansen, M.; Digest of Technical Papers, Pulsed Power Plasma Science, 2001. PPPS-2001. Volume 2, 17-22 June 2001 Page(s):905 - 908 vol.2
Abstract:  Explosively driven magnetic flux compression has been the object of research for more than three decades. Recently heightened interest has been focused on the basic physical mechanisms that determine the performance of helical magneto cumulative generators (MCGs). Two single-pitch helical flux compression generators of different sizes have been tested using current-voltage probes and optical diagnostics. The main parameters used to characterize the experimental performance of the flux compression generators were the flux conservation and theoretical current gain of each type of generator. Helices with constant pitch and differing separation between wires as well as wires with different insulation thickness were tested and analyzed with respect to their flux conservation and theoretical current gain. Preliminary results show that the insulation thickness plays only a minor role for a change in flux conservation due to geometry in the range from 0.01 to 0.5 mm provided that no internal breakdown occurred. Additionally, the overall physical dimension of the generator was modified to allow for a substantial increase in initial inductance. The outer diameter of the generator armature was held constant at 1.5 inches and the coil diameter was varied from 2.6 to 3.5 inches (expansion ratio of 1.7 or 2.3, respectively). The results gained from the conservative expansion ratio of 1.7 were used as a base to compare to the generator performance at the more aggressive expansion ratio of 2.3. First results show that an expansion ratio of 2.3 produces viable results for a partially annealed Aluminum armature with a Gurney angle of approximately 15 degrees.

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+ The Current Mode of Pulsed Power Generation in Moving Magnet Systems
  "The Current Mode of Pulsed Power Generation in Moving Magnet Systems", Proceedings of 13th IEEE International Pulsed Power Conference, Las Vegas, Nevada, June 2001, p. 228 (with S.I. Shkuratov, M. Kristiansen, J.C. Dickens, and J.C. Hernandez).
Abstract:  Not Available
+ Theoretical Treatment of Explosive Driven Ferroelectric Generators
  "Theoretical Treatment of Explosive Driven Ferroelectric Generators", Proceedings of 13th IEEE International Pulsed Power Conference, Las Vegas, Nevada, June 2001, p. 231 (with L.L. Altgilbers, Y. Tkach, S.I. Shkuratov, M. Kristiansen, J.C. Dickens, P.T. Tracy).
Abstract:  Not Available
+ Thermodynamic state of the magnetic flux compression generator volume
  Neuber, A.A.; Holt, T.A.; Dickens, J.C.; Kristiansen, M.; IEEE Conference Record - Abstracts, 2001 IEEE Conference on Pulsed Power Plasma Science, 17-22 June 2001 Page(s):151
Abstract:  Summary form only given, as follows.The knowledge of the thermodynamic state of the gas trapped in a helical flux compression generator is crucial for the assessment of flux loss due to internal electrical breakdown/arcing. Besides the helix deformation and armature deceleration at extremely high current amplitudes approaching 1 MA, the thermodynamic state of the shocked and compressed gas causes problems in the prediction of the generator output current vs. time towards the end of generator operation. Such a breakdown is experimentally detected as an abrupt change in the time derivative of the current waveform and it is easily distinguished from partial turn skipping by its sharper fall and non-periodic occurrence. The thermodynamic state of the generator was measured using primarily optical emission spectroscopy. 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, possibly as low as 2,000 K. (2) The intermediate stage during 14 to 4 microseconds before generator burnout that exhibits mainly an atomic copper line transition at about 0.8 eV. (3) The last few microseconds that reveal a highly compressed gas with temperatures of about 5,000 K and pressures of about 200 bar. Most experiments were conducted in air initially at STP, some results are given for SF6 initially at one atmosphere. In order to link the thermodynamic state to the breakdown sensitivity, additionally, simple conductivity measurements were conducted in current-free flux compression generator models

[PDF]

Publication Year:  2000
+ 3-D PIC Simulation of a Coaxial Vircator
  "3-D PIC Simulation of a Coaxial Vircator", 13th International Conference on High-Power Particle Beams, June 2000, Nagaoka, Japan (with W. Jiang, (Nagaoka University of Technology), and Jim Dickens.
Abstract:  Not Available
+ Energy Balance of Shock Wave Ferromagnetic Generators
  "Energy Balance of Shock Wave Ferromagnetic Generators", Proceedings of 12th Symposium on High Current Electronics, Tomsk, Russia, Sept. 24-29, 2000 (with S.I. Shkuratov and J. Dickens).
Abstract:  Not Available
+ Fundamental Studies of a Helical Magnetic Flux Compression Generator
  A. Neuber, J. Dickens, M. Giesselmann, B. Freeman, J. Rasty, H. Krompholz, and M. Kristiansen: Fundamental Studies of a Helical Magnetic Flux Compression Generator. Proceedings of the 13th International Conference on High-Power Particle Beams, June 25-30, 2000, Nagaoka, Japan.
Abstract:  Not Available
+ Fundamental studies of a simple helical magnetic flux compression generator
  Neuber, A.; Dickens, J.; Giesselmann, M.; Freeman, B.; Rasty, J.; Krompholz, H.; Kristiansen, M.; IEEE Conference Record - Abstracts. The 27th IEEE International Conference on Plasma Science, 2000. ICOPS 2000. 4-7 June 2000 Page(s):276
Abstract:  Summary form only given, as follows. The design of a helical flux compression generator, driven by 150 g of high explosives, for basic studies is presented and experimental results are discussed in comparison to numerical simulations. Simulation of the electric current output with the commercial circuit simulator PSPICE shows that this generator conserves the magnetic flux ideally in the low current mode, <30 kA. At current amplitudes in excess of 100 kA heating and melting of the single wound helix wire, AWG 12, limit the current flow. The volume between armature and stator is spectroscopically probed with fiber optics and valuable insight into the state of the shocked and compressed gas is gained. The same fiber optic probes are used to measure the velocity of the armature-stator contact along the generator axis. This contact velocity is largely affected by armature end effects, mainly due to the pressure loss at the detonator end. Both gas temperature and contact velocity have been successfully simulated with LS-DYNA3D, a three dimensional finite element hydrodynamic code. The generator's magnetic field structure is briefly discussed and magnetic field probe measurements are presented

[PDF]

+ Helical Flux Compression Generator for Basic Research
  A. Neuber, J. Dickens, M. Giesselmann, B. Freeman, P. Worsey, H. Krompholz, and M. Kristiansen, “Helical Flux Compression Generator for Basic Research,” 12th Symposium on High Current Electronics, September 25-29, 2000, Tomsk, Russia.
Abstract:  Not Available
+ High Power Microwave Window Breakdown under Vacuum and Atmospheric Conditions
  A. Neuber, D. Hemmert, J. Dickens, H. Krompholz, L. L. Hatfield, and M. Kristiansen: High Power Microwave Window Breakdown under Vacuum and Atmospheric Conditions. Proceedings of the SPIE conference, vol. 4031, pp. 90-98, Aerosense 2000, 24-28 April 2000, Orlando Florida.
Abstract:  Not Available
+ High-Power Microwave Generation by a Coaxial Vircator
  "High-Power Microwave Generation by a Coaxial Vircator", 13th International Conference on High-Power Particle Beams, June 2000, Nagaoka, Japan (with W. Jiang (Nagaoka University of Technology), and Jim Dickens).
Abstract:  Not Available
+ Studies on a Helical Magnetic Flux Compression Generator
  A. Neuber, J. Dickens, B. Freeman, P. Worsey, H. Krompholz, and M. Kristiansen: Studies on a Helical Magnetic Flux Compression Generator. Proceedings of the SAE Power Systems Conference, October 31-November 2, 2000, San Diego, CA.
Abstract:  Not Available
Publication Year:  1999
+ Development of improved triggered vacuum switches
  Warren, T.; Dickens, J.; Neuber, A.; Kristiansen, M.; Frazier, G.; McNab, I.R.; Digest of Technical Papers. 12th IEEE International Pulsed Power Conference, 1999. Volume 2, 27-30 June 1999 Page(s):1264 - 1267 vol.2
Abstract:  Triggered vacuum switches (TVS) are being evaluated for use in energizing electrical loads that require rapid and efficient switching of currents on command as well as the ability to interrupt at current zero crossing. Relatively few switching alternatives are available at the high currents (>250 kA) and voltages (>10 kV) needed. The TVSs used in recent pulsed power systems have demonstrated an ability to switch significant currents and interrupt at the zero current crossing, but they are not yet as effective as desired. In particular, higher current operation and faster dielectric recovery would be beneficial. The intent of this research is to expand the understanding of the physics of the vacuum switch (especially the opening phase) and to extend the operating parameters

[PDF]

+ Energy Efficiency Analysis of an Inductive Storage System
  J. Kim, J. Zhang, M. Giesselmann, J. Dickens, J. Mankowski, M. Kristiansen, “Energy Efficiency Analysis of an Inductive Storage System”, Proceedings of the 12th IEEE International Pulsed Power Conference, Monterey, California, June 27-30, 1999.
Abstract:  Not Available
+ Energy efficiency analysis of an inductive storage system
  Kim, J.; Zhang, J.; Giesselmann, M.; Dickens, J.; Mankowski, J.; Kristiansen, M.; Digest of Technical Papers. 12th IEEE International Pulsed Power Conference, 1999. Volume 2, 27-30 June 1999 Page(s):1445 - 1448 vol.2
Abstract:  In this paper, the simulation and evaluation of energy efficiency and voltage amplification in an inductive energy storage system with resistive, capacitive and diode loads is presented. A numerical simulation with Mathcad shows that by proper reduction of the storage energy inductance and of the exploding fuse interruption time, the energy efficiency and voltage amplification can be greatly improved

[PDF]

+ High voltage subnanosecond corona inception
  Mankowski, J.; Dickens, J.; Kristiansen, M.; Lehr, J.; Prather, W.; Gaudet, J.; Digest of Technical Papers. 12th IEEE International Pulsed Power Conference, 1999. Volume 2, 27-30 June 1999 Page(s):1392 - 1395 vol.2
Abstract:  Corona discharges in ultra-wideband 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 ultra-wideband systems. The current work involves the voltage 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, N2, H2 , and SF6, were tested

[PDF]

+ High-Power Microwave Generation by Coaxial Vircator
  "High-Power Microwave Generation by Coaxial Vircator", Proc. 12th IEEE International Pulsed Power Conference, Monterey, CA, June 27-30, 1999 (with W. Jiang, K. Woolverton, J. Dickens).
Abstract:  Not Available
+ Influence of the microwave magnetic field on high power microwave window breakdown
  Hemmert, D.; Neuber, A.; Dickens, J.; Krompholz, H.; Hatfield, L.L.; Kristiansen, M.; IEEE Conference Record - Abstracts. 1999 IEEE International Conference on Plasma Science, 1999. ICOPS '99. 20-24 June 1999 Page(s):229
Abstract:  Summary form only given. Effects of the microwave magnetic field on window breakdown are investigated at the upstream and downstream side of a dielectric interface. Simple trajectory calculations of secondary electrons in an RF field show significant forward motion of electrons parallel to the microwave direction of propagation. The Lorentz-force due to the microwave magnetic field on high-energy secondary electrons might substantially influence the standard multipactor mechanism. As a result, the breakdown power level for the downstream side of a window would be higher than for the upstream side. This hypothesis was tested utilizing an S-band traveling wave resonant ring, powered by a 3 MW magnetron at 2.85 GHz, leading to a total power greater than 60 MW. Breakdown was studied on an interface geometry consisting of a thin alumina slab in the waveguide, oriented normal to the microwave propagation direction

[PDF]

+ Measurement of dynamic electrical conductivity of MFCG armature material under conditions of shock and high strain rate loading
  Rasty, J.; Xiaobin Le; Neuber, A.; Jiande Zhang; Dickens, J.; Digest of Technical Papers. 12th IEEE International Pulsed Power Conference, 1999. Volume 2, 27-30 June 1999 Page(s):708 - 711 vol.2
Abstract:  Characterization of changes in the conductivity during the shock loading process is of paramount importance in estimating the efficiency of magnetic flux compression generators (MFCG). In this study, the main emphasis was the characterization of dynamic conductivity of the armature material during the shock-loading phase. A Split Hopkinson Pressure Bar apparatus was utilized to subject as-received and annealed specimens of OFHC copper to various shock pressures. Experiments conducted to measure the resistivity of Cu specimens indicated that resistivity initially decreases, followed by a sharp increase before decreasing to a steady state value. Depending on the magnitude of the shock pressure, resistivity changes in excess of 200% were recorded

[PDF]

+ Optical Diagnostics on Helical Flux Compression Generators
  A. Neuber, J. Dickens, H. Krompholz, and M. Kristiansen: Optical Diagnostics on Helical Flux Compression Generators. 12th IEEE Int. Pulsed Power Conference, Monterey, CA (1999)
Abstract:  Not Available
+ Pulse Power Conditioning with a Transformer for an Inductive Energy Storage System
  M. Giesselmann, J. Zhang, T. Heeren, E. Kristiansen, J. Dickens, D. Castro, D. Garcia, M. Kristiansen, “Pulse Power Conditioning with a Transformer for an Inductive Energy Storage System”, Proceedings of the 12th IEEE International Pulsed Power Conference, Monterey, California, June 27-30, 1999.
Abstract:  Not Available
+ Pulsed Power Generation Using Ferromagnetic Circuits
  "Pulsed Power Generation Using Ferromagnetic Circuits", Proc. 12th IEEE International Pulsed Power Conference, Monterey, CA, June 27-30, 1999 (with S.I. Shkuratov, J. Dickens, L.L. Hatfield, and R. Martin).
Abstract:  Not Available
+ Pulsed, High Energy Testing of Resistors
  "Pulsed, High Energy Testing of Resistors", Proc. 12th IEEE International Pulsed Power Conference, Monterey, CA, June 27-30, 1999 (with S.I. Shkuratov, J. Dickens, L.L. Hatfield, and E. Horrocks).
Abstract:  Not Available
+ Simulation, Design and Test of a MOV Pulse Shaping Device for High Power Microwave Generators
  M. Giesselmann, T. Heeren, E. Kristiansen, J. Dickens, D. Castro, D. Garcia, M. Kristiansen, “Simulation, Design and Test of a MOV Pulse Shaping Device for High Power Microwave Generators”, Proceedings of the 12th IEEE International Pulsed Power Conference, Monterey, California, June 27-30, 1999.
Abstract:  Not Available
+ The Design of a compact Pulse Transformer
  J. Zhang, J. Dickens, M. Giesselmann, J. Kim, E. Kristiansen, J. Mankowski, D. Garcia, M. Kristiansen, “The Design of a compact Pulse Transformer”, Proceedings of the 12th IEEE International Pulsed Power Conference, Monterey, California, June 27-30, 1999.
Abstract:  Not Available
+ The design of a compact pulse transformer
  Zhang, J.; Dickens, J.; Giesselmann, M.; Kim, J.; Kristiansen, E.; Mankowski, J.; Garcia, D.; Kristiansen, M.; Digest of Technical Papers. 12th IEEE International Pulsed Power Conference, 1999. Volume 2, 27-30 June 1999 Page(s):704 - 707 vol.2
Abstract:  To improve the pulse shape and to obtain µs order pulse duration on a diode load in an inductive energy storage system, an oil-submerged compact pulse transformer with diameter of 20 cm and length of 70 cm has been designed and tested. From theoretical calculations, the parameters with primary inductance Lp=3.4 µH, secondary inductance Ls=90 µH, and coupling coefficient K=0.772 are obtained. To prevent breakdown, a conical secondary design is adopted. Under the condition of 500 kV operation voltage, the maximum electric field in the transformer is 205 kV/cm (in oil). The axial voltage distribution on the secondary is linear. Experiments have been done to test the insulation, the mechanical force and the coupling coefficient. The test results are consistent with the design parameters

[PDF]

+ The Role of Outgassing in Surface Flashover under Vacuum
  A. Neuber, J. Dickens, H. Krompholz, and M. Kristiansen: The Role of Outgassing in Surface Flashover under Vacuum. 12th IEEE Int. Pulsed Power Conference, Monterey, CA (1999), invited.
Abstract:  Not Available
Publication Year:  1998
+ Breakdown of dielectric/vacuum interfaces caused by high power microwaves
  Neuber, A.; Dickens, J.; Hemmert, D.; Krompholz, H.; Hatfield, L.L.; Kristiansen, M.; IEEE Conference Record - Abstracts. 1998 IEEE International on Plasma Science, 1998. 25th Anniversary. 1-4 June 1998 Page(s):205
Abstract:  Summary form only given. Physical mechanisms leading to microwave breakdown on dielectric/vacuum interfaces are investigated for power levels on the order of 100 MW at 2.85 GHz. A 3 MW magnetron with 3.5 µs pulse width, is coupled to an S-band traveling wave resonator which is kept at a pressure of 10-8 Torr. The investigation is focused on an interface geometry comprising a thin dielectric polymer slab in the waveguide, oriented vertical to the direction of wave propagation, and two field enhancement tips placed in the middle of each waveguide broad wall. This ensures an almost purely tangential field at the interface surface and a localized breakdown

[PDF]

+ High voltage subnanosecond dielectric breakdown
  Mankowski, J.; Dickens, J.; Kristiansen, M.; IEEE Conference Record - Abstracts. 1998 IEEE International on Plasma Science, 1998. 25th Anniversary. 1-4 June 1998 Page(s):270
Abstract:  Summary form only given, as follows. Present day ultra-wideband (UWB) radiation sources a produce Megavolt pulses at 100's 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 non-existent. In support of the design of these UWB sources, we are investigating the breakdown characteristics, at these voltages and time lengths, of several liquids and gases. These include air, N2, H2, He, SF6, and transformer oil. The two voltage sources used in the experiments are capable of delivering 400 and 700 kV with a 400 ps risetime into an open load. These pulses are applied to the test gap area, capable of housing various gases and liquids at pressures from less than 1 to 150 atm. An empirical relationship of E-field versus breakdown time for the observed dielectrics is presented. Several other breakdown phenomena at these fast risetimes are observed. Dielectric breakdown strength dependence on polarity is investigated. Streak camera images of arc formation are captured, providing information on gap closure velocity. Also observed is the effect of ultraviolet radiation on the statistical lag time of breakdown for gas dielectrics at various pressures

[PDF]

+ Simulation, Design and Construction of a Pulsed Power Supply for High Power Microwaves Using Explosively Driven Magnetic Flux Compression
  M. Kristiansen, J. Dickens, T. Hurtig, M. Giesselmann, E. Kristiansen, “Simulation, Design and Construction of a Pulsed Power Supply for High Power Microwaves Using Explosively Driven Magnetic Flux Compression”, Proceedings of the 1998 MegaGauss Conference, ISBN 982-256-016-5, Tallahassee, Florida, October 18 – 23, 1998, p. 425…428.
Abstract:  Not Available
Publication Year:  1997
+ A subnanosecond high voltage pulser for the investigation of dielectric breakdown
  Mankowski, J.; Dickens, J.; Kristiansen, M.; Pulsed Power Conference, 1997. 1997 11th IEEE International Digest of Technical Papers. Volume 1, 29 June-2 July 1997 Page(s):549 - 554 vol.1
Abstract:  A high voltage, sub-nanosecond pulser is designed and built for the purposes of investigating dielectric breakdown. The requirement for the pulser is a voltage pulse of several hundred kilovolts, pulsewidth less than a few nanoseconds, and a risetime <400 psec. This is achieved by using pulse sharpening techniques on the output of a 500 kV Marx bank. Originally designed to stimulate a lightning strike, the voltage waveform from the Marx generator has a slow decay time of tens of µsec. In order to obtain a more desirable pulse, the Marx bank is modified. By removing a lumped-element resistor a higher peak output voltage with a faster risetime can be obtained. Circuit simulations have shown the capability of achieving an 800 kV output in less than 40 nsec to a charging (pulse forming) line. The 50 O impedance, oil-filled, pulse forming line consists of a peaking gap and pulse slicing gap. The peaking gap decreases the risetime of the applied pulse down to about 300 psec. The pulse slicing gap is included to short the voltage applied to the delay line and test chamber

[PDF]

+ Evaluation of a Russian SOS Diode for use in a Compact Modulator System
  J. Dickens, M. Kristiansen, M. Giesselmann and J.G. Kim, "Evaluation of a Russian SOS Diode for use in a Compact Modulator System", Proceedings of the 11th IEEE International Pulsed Power Conference, Baltimore, Maryland, June 29 - July 02, 1997.
Abstract:  Not Available
+ Evaluation of a Russian SOS Diode for Use in a Compact Modulator System
  "Evaluation of a Russian SOS Diode for Use in a Compact Modulator System", Proc. 11th IEEE Int’l. Pulsed Power Conf., Baltimore, MD June 29-July 2, 1997 (with J. Dickens).
Abstract:  Not Available
+ Window and Cavity Breakdown caused by High Power Microwaves
  A. Neuber, J. Dickens, D. Hemmert, H. Krompholz, L. L. Hatfield, and M. Kristiansen: Window and Cavity Breakdown caused by High Power Microwaves. IEEE International Conference on Plasma Science, San Diego (1997)
Abstract:  Not Available
+ Window and Cavity Breakdown caused by High Power Microwaves
  A. Neuber, J. Dickens, D. Hemmert, H. Krompholz, L. L. Hatfield, and M. Kristiansen: Window and Cavity Breakdown caused by High Power Microwaves. 11th IEEE Int. Pulsed Power Conf., Baltimore (1997)
Abstract:  Not Available
+ Window and Cavity Breakdown caused by High Power Microwaves
  A. Neuber, J. Dickens, D. Hemmert, H. Krompholz, L. L. Hatfield, and M. Kristiansen: Window and Cavity Breakdown caused by High Power Microwaves. International Workshop on High Power Microwave Generation and Pulse Shortening, Edinburgh UK (1997)
Abstract:  Not Available
Publication Year:  1996
+ Breakdown at window interfaces caused by high power microwave fields
  J.C. Dickens, J. Elliott, L.L. Hatfield, M. Kristiansen, H. Krompholz, “Breakdown at window interfaces caused by high power microwave fields”, International Symposium on Optical Science, Engineering, and Instrumentation - SPIE’s Annual Meeting, Denver, CO, August 4-9, 1996, published in SPIE proceedings Volume 2843, “Intense Microwave Pulses IV”, pg.153
Abstract:  Not Available
+ Compact Modulator Using Inductive Energy Storage and a Solid State Opening Switch
  "Compact Modulator Using Inductive Energy Storage and a Solid State Opening Switch", 1996 22nd International Power Modulator Symposium, Boca Raton, FL, June 24-27, 1996 (with James C. Dickens and John Bridges).
Abstract:  Not Available
Publication Year:  1995
+ Plume Model of Hall Effect Plasma Thrusters with Temporal Consideration
  "Plume Model of Hall Effect Plasma Thrusters with Temporal Consideration", XXIV International Electric Propulsion Conference, Moscow, Russia, Sept. 19-23, 1995 (with J.C. Dickens, E. O’Hair and M. Kristiansen).
Abstract:  Not Available
Publication Year:  1993
+ Electrode Performance of a Three Electrode, Triggered, High Energy Spark Gap Switch
  "Electrode Performance of a Three Electrode, Triggered, High Energy Spark Gap Switch", 9th IEEE Pulsed Power Conference, Albuquerque, NM, June 21-23, 1993 (with J.C. Dickens and T.G. Engel).
Abstract:  Not Available
Publication Year:  1992
+ 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", 6th Electromagnetic Launch Technology, April 28-30, 1992, Austin, TX (with T.G. Engel and J.C. Dickens).
Abstract:  Not Available

Book

Publication Year:  2005
+ Power Conditioning, In: Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generator
  T. Heeren, M. Giesselmann, J. C. Dickens and A. Neuber, “Power Conditioning,” In: Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generator, A. Neuber Edtr., Springer Berlin Heidelberg New York, ISBN 3-540-26051-X, 2005.
Abstract:  Not Available