Dr. Andreas Neuber, Professor
Contact Information
Department of Electrical and Computer Engineering
Texas Tech University
Lubbock, TX 79409-3102
Phone: (806)742-1250
Fax: (806)742-1281
andreas.neuber@ttu.edu
Education
- Dipl. Phys. (M.S.Phys.), Technical University of Darmstadt (Germany), 1990
- Ph.D. in M.E., Technical University of Darmstadt (Germany), 1996
Research Interests
- Electric Breakdown
- Gas-Laser Physics
- High Power Microwaves
- Pulsed Power Technology
Other Interests
- Nonlinear Laser Spectroscopy
- Fossil Fuel Combustion
Projects
- High Power Microwave Breakdown
- Electric Surface Flashover
- Explosively Driven Pulsed Power
Awards and Professional Societies
- Institute of Electrical and Electronics Engineers
- The IEEE Nuclear and Plasma Sciences Society
- The Optical Society of America
- The Deutsche Physikalische Gesellschaft
Publications
Journal
Publication Year: 2008
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Breakdown Delay Times for Subnanosecond Gas Discharges at Pressures Below One Atmosphere |
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J.E. Chaparro, W. Justis, H.G. Krompholz, L.L. Hatfield, A. A. Neuber, Breakdown Delay Times for Subnanosecond Gas Discharges at Pressures Below One Atmosphere, IEEE Transactions on Plasma Science 36, 2505 - 2511 (2008). |
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Abstract:
Not Available |
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Compact Electro-Explosive Fuses for Explosive Driven Pulsed Power |
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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) |
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Abstract:
Not Available |
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Compact High Power Microwave Generation |
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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. |
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Abstract:
Not Available |
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Effects of UV Illumination on Surface Flashover under Pulsed Excitation |
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J. T. Krile, A. A. Neuber, H. G. Krompholz, "Effects of UV Illumination on Surface Flashover under Pulsed Excitation", to appear in IEEE Transactions on Plasma Science (2008) |
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Abstract:
Undesirable surface flashover of high voltage support structures can severely limit the compactness of open air high voltage systems. Only recently, increased effort has been invested in characterizing and quantifying the physical processes involved in surface flashover occurring under atmospheric conditions and under the influence of UV illumination. In this paper, a UV flash lamp and a solid-state UV source, with its much faster turn-off time, were utilized in conjunction with a high temporal resolution testing apparatus. The UV pulse, excitation voltage, discharge current, and flashover self-luminosity were measured with high temporal precision. We relate recent experiments to our experimental findings of surface flashover under atmospheric conditions gained over the past five years. A simple model that describes the observed behavior will be presented. In addition, a more advanced Monte Carlo-type code for electron collision dynamics will be utilized to further analyze the role of UV in surface flashover under atmospheric conditions. |
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Fast-charging compact seed source for magnetic flux compression generators |
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M. Elsayed, M. Kristiansen, A. Neuber, Fast-charging compact seed source for magnetic flux compression generators, 2008 Review of Scientific Instruments. Vol. 79, 124702. |
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Abstract:
Not Available |
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High Current Surface Flashover in a High Pressure SF6 Environment |
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J. Krile, A. Neuber, R. Vela, "High Current Surface Flashover in a High Pressure SF6 Environment", to appear in IEEE Transactions on Plasma Science (2008) |
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Abstract:
Not Available |
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High Power Microwave Switching Utilizing A Waveguide Spark Gap |
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J. Foster, G. Edmiston, M. Thomas, A. Neuber, High Power Microwave Switching Utilizing A Waveguide Spark Gap, Rev. Sci. Instrum. 79, 114701 (2008). |
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Abstract:
Not Available |
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High Power Microwave System |
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T. Holt, A. Young, M. Elsayed, J. Walter, A. Neuber, and M. Kristiansen, "High Power Microwave System", to appear in IEEE Transactions on Plasma Science (2008) |
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Abstract:
Not Available |
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Images From the Development of a High-Power Microwave System |
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T. Holt, A. Young, M. Elsayed, J. Walter, A. Neuber, and M. Kristiansen, Images From the Development of a High-Power Microwave System, IEEE Transactions on Plasma Science 36, 1414-1415 (2008). |
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Abstract:
Not Available |
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Imaging of High Power Microwave Induced Surface Flashover on a Corrugated Dielectric Window |
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G. Edmiston, J. Krile, A. Neuber, "Imaging of High Power Microwave Induced Surface Flashover on a Corrugated Dielectric Window", to appear in IEEE Transactions on Plasma Science (2008) |
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Abstract:
Not Available |
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Seed Electron Production from O- Ions under High Power Microwave Excitation |
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G. F. Edmiston, A. A. Neuber, H. G. Krompholz, J. T. Krile, "Seed Electron Production from O- Ions under High Power Microwave Excitation", J. Appl. Phys. 103, 063303 (2008) |
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Abstract:
Not Available |
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Utilization of a Nonexplosive Test Bed for Flux-Compression-Generator Electroexplosive Opening Switches |
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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). |
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Abstract:
Not Available |
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Publication Year: 2007
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Contributing Factors to Window Flashover Under Pulsed High Power Microwave Excitation at High Altitude |
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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) |
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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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Dielectric Surface Flashover at Atmospheric Conditions with Unipolar Pulsed Voltage Excitation |
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Morales, K.; Krile, J.; Neuber, A.; Krompholz, H.;
IEEE Transactions on Dielectrics and Electrical Insulation, [see also IEEE Transactions on Electrical Insulation], Volume 14, Issue 4, Aug. 2007 Page(s):774 - 782 |
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Abstract:
Not Available |
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IEEE Transactions on Dielectrics and Electrical Insulation |
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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 |
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Abstract:
Not Available |
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Interface Breakdown During High-Power Microwave Transmission |
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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 |
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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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Pulsed Dielectric Surface Flashover in an SF6 Environment |
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J. T. Krile, R. Vela, A. A. Neuber, and H. G. Krompholz, "Pulsed Dielectric Surface Flashover in an SF6 Environment", IEEE Transactions on Plasma Science 35, pp. 1580-1587 (2007) |
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Abstract:
A recently upgraded laser-triggered gas switch at Sandia National Laboratories has developed a failure mode that results in the breakdown spark tracking to the inside of the containment envelope. These breakdowns along the surface, or surface flashovers, degrade the performance of the overall switch, causing the switch to prefire in the successive shot. In the following, experimental results of pulsed surface flashover across different dielectric materials in SF6, primarily at atmospheric pressure, as well as flashover and volume breakdown in at pressures from 1.3 to 365.4 kPa are presented. In addition to fast voltage and current monitoring of the breakdown event, an increased emphasis was put on imaging the event as well as gathering optical emission spectra (~200-700 nm) from it. As much as possible, the small-scale experiments were designed to reproduce, at least partly, the conditions as they are found in the large 5-MV switch. An effort was made to determine what changes could be made to reduce the occurrence of surface flashovers, in addition to some broadly applicable conclusions on surface flashovers in an SF6 environment. |
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Spectral Analysis of Pulsed Volume Breakdown in SF6 at High Pressures |
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Krile, J. T.; Vela, R.; Neuber, A. A.; Krompholz, H. G.;
IEEE Transactions on Plasma Science, Volume 35, Issue 4, Part 3, Aug. 2007 Page(s):1163 - 1169 |
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Abstract:
The Z-machine, which is located at Sandia National Laboratories, is currently undergoing refurbishment to increase the output drive current. Due to increased switching voltage requirements, some switch failure modes have been identified with the laser-triggered gas switch design, including envelope surface flashover. In order to improve the performance and lifetime of these switches, a basic understanding of the underlying physics of the failure mechanisms is required. A small-scale experimental setup has been constructed to approximate conditions within the switch. The possible impact of the $hbox{SF}_{6}$ volume spark between the switch electrodes on the envelope surface flashover is investigated. Measured optical spectra of the $ hbox{SF}_{6}$ volume spark over a wide pressure range, from rough vacuum to 40 psig overpressure, are analyzed regarding their potential to contribute to switch failure |
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Publication Year: 2006
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Conduction and breakdown mechanismsin transformer oil |
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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 |
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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 |
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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) |
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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 |
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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 |
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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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Monte Carlo simulation of HPM window breakdown at atmospheric conditions |
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John T. Krile, Andreas A. Neuber, Hermann G. Krompholz, and Thomas L. Gibson, Monte Carlo simulation of HPM window breakdown at atmospheric conditions. Applied Physics Letters vol. 89, 201501 (2006). |
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Abstract:
Not Available |
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Phenomenology of subnanosecond gas discharges at pressures below one atmosphere |
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Krompholz, H.G.; Hatfield, L.L.; Neuber, A.A.; Kohl, K.P.; Chaparro, J.E.; Han-Yong Ryu;
IEEE Transactions on Plasma Science, Volume 34, Issue 3, Part 3, June 2006 Page(s):927 - |
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Abstract:
Volume breakdown and surface flashover in quasi-homogeneous applied fields in 10/sup -5/ to 600 torr argon and dry air are investigated, using voltage pulses with 150 ps risetime, <1ns duration, and up to 150 kV amplitude into a matched load. The test system consists of a transmission line, a transition to a biconical section, and a test gap, with gap distances of about 1mm. The arrangement on the other side of the gap is symmetrical. Diagnostics include fast capacitive voltage dividers, for determination of voltage waveforms in the gap, and conduction current waveforms through the gap. X-ray diagnostics use a scintillator-photomultiplier combination with different absorber foils yielding coarse spectral resolution. Optical diagnostics include use of a streak camera to get information on the discharge channel geometry and dynamics, and temporally resolved measurements with photomultipliers. Breakdown delay times are on the order of 100-400 ps, with minima occurring in the range of several 10torr. X-ray emission extends to pressures >100 torr, indicating the role of runaway electrons during breakdown. Maximum X-ray emission coincides with shortest breakdown delay times at several 10 torr. Simple modeling using the average force equation and cross sections for momentum transfer and ionization supports the experimental results |
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Pulsed dielectric surface flashover in nitrogen at atmospheric conditions |
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Morales, K.P.; Krile, J.T.; Neuber, A.A.; Krompholz, H.G.;
IEEE Transactions on Dielectrics and Electrical Insulation, Volume 13, Issue 4, Aug. 2006 Page(s):803 - 809 |
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Abstract:
Dielectric flashover along insulators in vacuum has been comprehensively researched in the past. Less studied, but of similar importance, is surface flashover at atmospheric
pressures and the impact of an atypical electrode geometry, humidity, and ultraviolet (UV) illumination. Previous research has shown distinct discharge behavior in air and nitrogen environments for an electrode geometry in which the applied electric field lines curve above the dielectric surface. It was concluded that the discharge development path, whether along the electric field lines or the surface of the dielectric, is related to
the oxygen content in the atmospheric background. It is believed that this dependence is due to the discharge’s production of UV radiation in an oxygen rich environment. Thus, experiments were conducted in a nitrogen environment employing UV surface
illumination in order to observe the affects on the flashover spark behavior. From the experimental data, it can be ascertained that UV illumination and intensity play a significant role in the discharge development path. Based on these results an
explanation of the physical mechanisms primarily involved in unipolar surface flashover will be presented. Additional experiments regarding the effects of humidity on the discharge behavior will be discussed as well. |
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Similarities Of Dielectric Surface Flashover at Atmospheric Conditions for Pulsed Unipolar and RF Excitation |
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J. Krile, G. Edmiston, K. Morales, A. Neuber, H. Krompholz, and M. Kristiansen, Similarities Of Dielectric Surface Flashover at Atmospheric Conditions for Pulsed Unipolar and RF Excitation, Laser Physics in Special Issue "Plasma, Beams, and Lasers" Dedicated to Professor Gennady A. Mesyats on his 70th Birth Anniversary, vol. 16, pp. 194-201, 2006. |
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Abstract:
Not Available |
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Publication Year: 2005
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DC and Pulsed Dielectric Surface Flashover at Atmospheric Pressure |
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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 |
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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 |
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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) |
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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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Guest Editorial Special Issue on Power Modulators and Repetitive Pulsed Power |
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Kirkici, H.; Neuber, A.; Umstattd, R.J.;
IEEE Transactions on Plasma Science, Volume 33, Issue 4, Part 1, Aug. 2005 Page(s):1134 - 1135 |
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Abstract:
Not Available |
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Imaging of dielectric surface flashover in atmospheric conditions |
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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 |
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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 |
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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 |
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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 |
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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. |
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Abstract:
Not Available |
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Publication Year: 2004
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DC flashover of a dielectric surface in atmospheric conditions |
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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 |
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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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Magnetic flux compression Generators |
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Neuber, A.A.; Dickens, J.C.;
Proceedings of the IEEE
Volume 92, Issue 7, July 2004 Page(s):1205 - 1215 |
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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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Modern Pulsed Power: Charlie Martin and Beyond |
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Schamiloglu, E.; Barker, R.J.; Gundersen, M.; Neuber, A.A.;
Proceedings of the IEEE on Pulsed Power Technology, Volume 92, Issue 7, July 2004 Page(s):1014 - 1020 |
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Abstract:
In this introduction to the Special Issue on pulsed power and its applications, background information is provided for the nonspecialist to better understand the many challenges in designing pulsed power systems, and the wide diversity of applications that are now emerging. The approach to providing a tutorial on pulsed power technology is to make available to the reader the paper written by J. C. Martin which appeared in a Special Section of the Proceedings of the IEEE on pulsed power technology in June 1992. That paper is supplemented in this introduction with additional information that complements many of the invited papers composing this Special Issue. |
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Quantification of ohmic and intrinsic flux losses in helical flux compression Generators |
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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 |
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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 |
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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 |
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Abstract:
Pulsed power is a technology that is suited to drive electrical loads requiring very large power pulses in short bursts (high-peak power). Certain applications require technology that can be deployed in small spaces under stressful environments, e.g., on a ship, vehicle, or aircraft. In 2001, the U.S. Department of Defense (DoD) launched a long-range (five-year) Multidisciplinary University Research Initiative (MURI) to study fundamental issues for compact pulsed power. This research program is endeavoring to: 1) introduce new materials for use in pulsed power systems; 2) examine alternative topologies for compact pulse generation; 3) study pulsed power switches, including pseudospark switches; and 4) investigate the basic physics related to the generation of pulsed power, such as the behavior of liquid dielectrics under intense electric field conditions. Furthermore, the integration of all of these building blocks is impacted by system architecture (how things are put together). This paper reviews the advances put forth to date by the researchers in this program and will assess the potential impact for future development of compact pulsed power systems |
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Scanning the Technology |
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E. Schamiloglou, R. J. Barker, M. Gunderson, and A. A. Neuber, “Scanning the Technology,” Proceedings of the IEEE, vol. 92, pp. 1014-1020, 2004. |
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Abstract:
Not Available |
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Publication Year: 2003
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Helical MFCG For Driving A High Inductance Load |
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Andreas A. Neuber, Juan-Carlos Hernández, James C. Dickens, Magne Kristiansen, Electromagnetic Phenomena, vol. 3, pp. 397-404, (2003). |
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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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Publication Year: 2002
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Field enhanced microwave breakdown in a plasma limiter |
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Mankowski, J.J.; Hemmert, D.; Neuber, A.; Krompholz, H.;
IEEE Transactions on Plasma Science, Volume 30, Issue 1, Part 1, Feb. 2002 Page(s):102 - 103 |
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Abstract:
A new type of plasma limiter is being developed which can turn on in less than 1 ns. The approach taken is to initiate streamer breakdown via a micron radius needle tip. Images were taken of the gap region in argon at several pressures in order to investigate the role of the tip region |
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High-speed optical diagnostic of an exploding wire fuse |
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Giesselmann, M.; Heeren, T.; Neuber, A.; Walter, J.; Kristiansen, M.;
IEEE Transactions on Plasma Science, Volume 30, Issue 1, Part 1, Feb. 2002 Page(s):100 - 101 |
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Abstract:
Explosive flux compression generators generate hundreds of kiloamperes and voltages of a few kilovolts. A power conditioning stage is required since typically voltages in the hundreds of kilovolts range are needed. Inductive energy storage systems with an opening switch provide the necessary voltage gain. In our application, the opening switch has been implemented as an exploding wire fuse. The voltage gain, and hence the performance of the system, is greatly dependent on the opening switch. We utilized high-speed optical imaging (up to 107 pictures/s) to assess the performance of the exploding wire fuse |
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Thermodynamic state of the magnetic flux compression generator volume |
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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 |
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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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Publication Year: 2001
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Electrical behavior of a simple helical flux compression generator for code benchmarking |
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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 |
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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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Studies on a Helical Magnetic Flux Compression Generator |
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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. |
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Abstract:
Not Available |
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Publication Year: 2000
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Dielectric/Gas Interface Breakdown Caused by High Power Microwaves |
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D. Hemmert, A. Neuber, H. Krompholz, L.L Hatfield, and M. Kristiansen: Dielectric/Gas Interface Breakdown Caused by High Power Microwaves. Proceedings of the 13th International Conference on High-Power Particle Beams, June 25-30, 2000, Nagaoka, Japan, invited. |
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Abstract:
Not Available |
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Microwave magnetic field effects on high-power microwave window breakdown |
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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 |
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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 |
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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 |
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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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The role of outgassing in surface flashover under vacuum |
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Neuber, A.A.; Butcher, M.; Krompholz, H.; Hatfield, L.L.; Kristiansen, M.;
IEEE Transactions on Plasma Science, Volume 28, Issue 5, Oct. 2000 Page(s):1593 - 1598 |
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Abstract:
Results of high-speed electrical and optical diagnostics are used as a basis to discuss a new surface flashover model. Outgassing, caused by electron stimulated desorption, is found to play a crucial role in the temporal flashover development. Dielectric unipolar surface flashover under vacuum is experimentally characterized by a three-phase development, which covers a current range from 10-4 A to 100 A. Phase one comprises a fast (several nanoseconds) buildup of a saturated secondary electron avalanche reaching current levels of 10 to 100 mA. Phase two is associated with a slow current amplification reaching currents in the Ampere level within typically 100 ns. The final phase is characterized by a fast current rise up to the impedance-limited current on the order of 100 A. The development during phase two and three is described by a zero-dimensional model, where electron-induced outgassing leads to a Townsend-like gas discharge above the surface. This is supported by time-resolved spectroscopy that reveals the existence of excited atomic hydrogen and ionic carbon before the final phase. The feedback mechanism toward a self-sustained discharge is due to space charge leading to an enhanced field emission from the cathode. A priori unknown model parameters, such as outgassing rate and gas density buildup above the surface, are determined by fitting calculated results to experimental data. The significance of outgassing is also discussed with a view to microwave surface flashover |
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Publication Year: 1999
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Dielectric surface flashover in vacuum at 100 K |
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Neuber, A.; Butcher, M.; Hatfield, L.L.; Kristiansen, M.; Krompholz, H.;
IEEE Transactions on Dielectrics and Electrical Insulation, [see also IEEE Transactions on Electrical Insulation], Volume 6, Issue 4, Aug. 1999 Page(s):512 - 515 |
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Abstract:
Cryogenic components in high power electrical systems and in power electronics gain more and more importance. The behavior of insulators for cryogenic conditions, however, is virtually unknown. In a fast coaxial setup, dielectric test sample and electrodes in vacuum are cooled to <100 K and flashover is characterized using fast electrical and optical diagnostics. Three consecutive development stages for flashover in self-breakdown mode with a gap distance of 0.5 cm can be distinguished: (1) a fast current rise to mA amplitudes within ~2 ns, probably associated with field emission, followed by, (2) a slow current rise to ~5 to 10 A amplitude with duration of 40 ns to 1 µs, associated with secondary emission avalanche saturation, and (3) a transition to a rapid gaseous ionization above the sample caused by electron induced outgassing, leading to impedance-limited current amplitudes of ⩽300 A. Phase (1) shows a higher final current at lower temperature, which is probably due to a higher initial velocity of the secondary electrons, the duration of phase (2) is a decreasing function of breakdown voltage and only slightly dependent on temperature, which points to a weak temperature dependence of the outgassing process. Flashover potentials show a slight increase at lower temperature |
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Electric Current in DC Surface Flashover in Vacuum |
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A. Neuber, M. Butcher, L. L. Hatfield, and H. Krompholz: Electric Current in DC Surface Flashover in Vacuum. J. Appl. Phys., vol. 15, 3084-3091 (1999) |
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Abstract:
Not Available |
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Imaging of high-power microwave-induced surface flashover |
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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 |
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Abstract:
Using two gated intensified digital charge-coupled device cameras, one sensitive in the near infrared to ultraviolet region and one in the soft X-ray region, the temporal development of high-power microwave-induced surface flashover across a vacuum/dielectric interface has been imaged. The emission of X-ray radiation from the interface is caused by field emitted electrons accelerated in the high electromagnetic field impacting the solid. This generation of bremsstrahlung terminates at the moment of full flashover development that is indicated by the optical light emission. A rising plasma density above the dielectric surface due to electron induced outgassing triggers this behavior |
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Initiation of High Power Microwave Dielectric Interface Breakdown |
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A. Neuber, D. Hemmert, H. Krompholz, L. Hatfield, and M. Kristiansen: Initiation of High Power Microwave Dielectric Interface Breakdown. J. Appl. Phys., vol. 86, 1724-1728 (1999). |
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Abstract:
Not Available |
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Publication Year: 1998
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Finite Rate Chemistry and NO Molefraction in Non-Premixed Turbulent Flames |
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A. Neuber, G. Krieger, M. Tacke, E. Hassel, and J. Janicka: Combustion and Flame, vol. 113, 198-211 (1998) |
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Abstract:
Finite rate chemistry is investigated in turbulent N2-diluted H2 diffusion flames by means of laser spectroscopic methods and a numerical model of combustion. The major species occurring in these hydrogen flames or the temperature are measured with SRS (Spontaneous Raman Spectroscopy) or Rayleigh spectroscopy. Some minor species, the radical OH and the pollutant NO, are simultaneously measured with linear LIF (Laser Induced Fluorescence). Multidimensional pdfs (probability density function) can be deduced from these measurements. Use is made of a numerical model with two principal variables, mixture fraction ? and reaction progress variable ?, as a basis for discussion of the experimental results. A k-e-turbulence model together with a two-dimensional presumed pdf for the coupling of turbulence and chemistry are applied. So, experimental two-dimensional pdfs as well as mean values of ? and ? as functions of the position in the flame are deduced from the simultaneous measurements. The experimental and theoretical spatial maxima of the mean OH molefraction agree well in magnitude, despite the correlation coefficient between ? and ? of the measured pdf can be as high as 0.5. The neglect of this covariance for the calculation of the presumed pdf is quantified. It results in clear deviations for the OH molefraction. The experimental NO and OH molefractions are better simulated by flame calculations carried out with the presented combustion model than by the also shown calculations based on a single variable for description of chemistry. |
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Window breakdown caused by high-power microwaves |
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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 - |
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Abstract:
Physical mechanisms leading to microwave breakdown on windows are investigated for power levels on the order of 100 MW at 2.85 GHz. The test stand uses a 3-MW magnetron coupled to an S-band traveling wave resonator. Various configurations of dielectric windows are investigated. In a standard pillbox geometry with a pressure of less than 10-6 Pa, surface discharges on an alumina window and multipactor-like discharges starting at the waveguide edges occur simultaneously. To clarify physical mechanisms, window breakdown with purely tangential electrical microwave fields is investigated for special geometries. Diagnostics include the measurement of incident/reflected power, measurement of local microwave fields, discharge luminosity, and X-ray emission. All quantities are recorded with 0.21-ns resolution. In addition, a framing camera with gating times of 5 ns is used. The breakdown processes for the case with a purely tangential electric field is similar to DC flashover across insulators, and similar methods to increase the flashover field are expected to be applicable |
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Conference Paper/Presentation
Publication Year: 2008
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A Compact, Self-Contained High Power Microwave Source Based on a Reflex-Triode Vircator and Explosively Driven Pulsed Power |
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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. |
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Abstract:
Not Available |
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Capacitor Evaluation For Compact HV Pulse Generation |
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E. J. Matthews, A. A. Neuber, M. Kristiansen, Capacitor Evaluation For Compact HV Pulse Generation, to be published in the Proceedings of the 2008 IEEE International Power Modulator Conference Las Vegas, Nevada, USA, May 27-31, 2008. |
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Abstract:
Not Available |
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Compact High Power Microwave Generation |
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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. |
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Abstract:
Not Available |
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Compact Silicon Carbide Switch For High Voltage Operation |
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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 |
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Abstract:
Not Available |
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Comparison of HFCG and Compact Marx for Driving a High Power Microwave Load |
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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. |
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Abstract:
Not Available |
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Energy Deposition and Electromagnetic Compatibility Assessment of Electroexplosive Devices |
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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 |
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Abstract:
Not Available |
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High-Current Compact FCG Seed Source Implementing Solid State Switching |
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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. |
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Abstract:
Not Available |
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Opening Switch Utilizing Stress Induced Conduction In PMMA |
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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. |
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Abstract:
Not Available |
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Particle Simulation of Ultrafast Closing Switch at Sub-Atmospheric Pressures |
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Jordan Chaparro, Hermann Krompholz, Andreas Neuber, Lynn Hatfield, Particle Simulation of Ultrafast Closing Switch at Sub-Atmospheric Pressures, IEEE International Power Modulator Conference, Las Vegas, NV, May 27-31, 2008 |
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Abstract:
Not Available |
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Scaling and Improvement of Compact Explosively-Driven Ferroelectric Generators, |
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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. |
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Abstract:
Not Available |
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Short Rise Time High Power Microwave Induced Surface Flashover At Atmospheric Pressures |
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J. Foster, G. Edmiston, J. Krile, A. Neuber, and H. Krompholz, Short Rise Time High Power Microwave Induced Surface Flashover At Atmospheric Pressures, to be published in the Proceedings of the 2008 IEEE International Power Modulator Conference Las Vegas, Nevada, USA, May 27-31, 2008. |
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Abstract:
Not Available |
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Statistical and Formative Delay Times for Sub-Nanosecond Breakdown at Sub-Atmospheric Pressure |
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Jordan Chaparro, Lynn Hatfield, Hermann Krompholz, Andreas Neuber, Statistical and Formative Delay Times for Sub-Nanosecond Breakdown at Sub-Atmospheric Pressure, IEEE International Power Modulator Conference, Las Vegas, NV, May 27-31, 2008 |
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Abstract:
Not Available |
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Statistics of High Power Microwave Induced Window Flashover |
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A. Neuber, G. Edmiston, J. Krile, J. Foster, H. Krompholz, Statistics of High Power Microwave Induced Window Flashover, presented at the 35th IEEE International Conference on Plasma Science, June 15 - 19, 2008, Karlsruhe, Germany |
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Abstract:
Not Available |
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Window Flashover Initiation Under Pulsed Microwave Excitation |
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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. |
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Abstract:
Not Available |
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Publication Year: 2007
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Dielectric Surface Flashover at Atmospheric Conditions under High Power Microwave Excitation |
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A. Neuber, J. T. Krile, G. F. Edmiston, H. G. Krompholz, "Dielectric Surface Flashover at Atmospheric Conditions under High Power Microwave Excitation", Phys. Plasmas 14, 057102 (2007) (invited). |
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Abstract:
Not Available |
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Dielectric Surface Flashover under Pulsed Unipolar and RF Excitation |
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A. Neuber, “Dielectric Surface Flashover under Pulsed Unipolar and RF Excitation,” presented at the DPG Frühjahrstagung des AMOP, Düsseldorf, March 19-23, 2007, Germany (invited plenary presentation) |
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Abstract:
Not Available |
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Effects of UV Illumination on Surface Flashover under Pulsed Unipolar Excitation |
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J. T. Krile, A. A. Neuber, H. G. Krompholz, "Effects of UV Illumination on Surface Flashover under Pulsed Unipolar Excitation," presented at the 2007 IEEE Pulsed Power and Plasma Science Conference, Albuquerque, NM June 17-22, 2007 (invited). |
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Abstract:
Not Available |
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Electro-Explosive Fuse Optimization for Helical Flux Compression Generator Using a Non-Explosive Test Bed |
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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. |
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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. |
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Experimental investigation of subnanosecond gas breakdown in the E/p range 10^3 to 10^5 V/cm torr |
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H. Krompholz, L. Hatfield, A. Neuber, P, J. Chaparro, and W. Justis, “Experimental investigation of subnanosecond gas breakdown in the E/p range 103 to 105 V/cm torr,” in Proceedings of the 28th ICPIG, July 15-20, 2007, Prague, Czech Republic, pp. 1014-1017. |
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Abstract:
Not Available |
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Fuse and Load Testing with Mid-Sized, High Energy Density Flux Compression Generators, |
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A. J. Young, T. A. Holt, M. A. Elsayed, A. A. Neuber, M. Kristiansen, L. L. Altgilbers, A. H. Stults, "Fuse and Load Testing with Mid-Sized, High Energy Density Flux Compression Generators," presented at the 2007 IEEE Pulsed Power and Plasma Science Conference, Albuquerque, NM June 17-22, 2007. |
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Abstract:
Not Available |
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Initiation of HPM Surface Flashover |
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G. F. Edmiston, A. A. Neuber, J. T. Krile, L. M. McQuage, H. Krompholz, "Initiation of HPM Surface Flashover," presented at the 2007 IEEE Pulsed Power and Plasma Science Conference, Albuquerque, NM June 17-22, 2007. |
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Abstract:
Not Available |
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Investigation of an FCG and Pulse Transformer Based Power Conditioning System |
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T. A. Holt, A. J. Young, M. A. Elsayed, A. A. Neuber, M. Kristiansen, K. A. O'Connor, R. D. Curry, "Investigation of an FCG and Pulse Transformer Based Power Conditioning System," presented at the 2007 IEEE Pulsed Power and Plasma Science Conference, Albuquerque, NM June 17-22, 2007. |
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Abstract:
Not Available |
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Opening Switch Utilizing Shock Wave Induced Conduction in PMMA and PVC |
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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 |
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Abstract:
Not Available |
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Pulsed Volume and Surface Discharges in an SF6 Environment |
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R. Vela, J. T. Krile, A. A. Neuber, H. G. Krompholz, "Pulsed Volume and Surface Discharges in an SF6 Environment," presented at the 2007 IEEE Pulsed Power and Plasma Science Conference, Albuquerque, NM June 17-22, 2007. |
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Abstract:
Not Available |
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Scaling Laws for Sub-Nanosecond Breakdown in Gases with Pressures below One Atmosphere |
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W. H. Justis, J. E. Chaparro, H. G. Krompholz, L. L. Hatfield, A. A. Neuber, "Scaling Laws for Sub-Nanosecond Breakdown in Gases with Pressures below One Atmosphere," presented at the 2007 IEEE Pulsed Power and Plasma Science Conference, Albuquerque, NM June 17-22, 2007. |
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Abstract:
Not Available |
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Seed Electron Model for Monte Carlo HPM Breakdown Model |
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A. Neuber, G. Edmiston1, H. Krompholz, “Seed Electron Model for Monte Carlo HPM Breakdown Model,” in Proceedings of the 28th ICPIG, July 15-20, 2007, Prague, Czech Republic, pp. 1042-1045. |
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Abstract:
Not Available |
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Short Pulse High Power Microwave Surface Flashover |
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L. M. McQuage, G. F. Edmiston, J. P. Mankowski, A. A. Neuber, "Short Pulse High Power Microwave Surface Flashover," presented at the 2007 IEEE Pulsed Power and Plasma Science Conference, Albuquerque, NM June 17-22, 2007. |
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Abstract:
Not Available |
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X-Ray Emission from Sub-Nanosecond Gas Breakdown |
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J. E. Chaparro, W. H. Justis, H. G. Krompholz, L. L. Hatfield, A. A. Neuber, "X-Ray Emission from Sub-Nanosecond Gas Breakdown," Proceedings of the 2007 IEEE Pulsed Power and Plasma Science Conference, pp. 1652-1655, Albuquerque, NM June 17-22, 2007. |
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Abstract:
Not Available |
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Publication Year: 2006
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A Fabrication Method for a Mid-Sized, High Energy-Density, Flux Compression Generator |
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T.A. Holt, A.J. Young, A.A. Neuber, M. Kristiansen, “A Fabrication Method for a Mid-Sized, High Energy-Density, Flux Compression Generator” presented at the 2006 International Conference on Megagauss Magnetic Field Generation and Related Topics, November 5-10, 2006 Santa Fe, New Mexico, USA |
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Abstract:
Not Available |
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A Fabrication Method for Helical Flux Compression Generators |
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T.A. Holt, A.J. Young, A.A. Neuber, M. Kristiansen, “A Fabrication Method for Helical Flux Compression Generators,” presented at the 2006 Megagauss XI Conference, Sept. 10-14, 2006, Imperial College, London, UK |
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Abstract:
Not Available |
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A Flux Compression Generator Non-Explosive Test Bed for Explosive Opening Switches |
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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 |
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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 |
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Advanced Compact Pulsed Power for Directed Energy Weapons |
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A. Neuber, “Advanced Compact Pulsed Power for Directed Energy Weapons,” Directed Energy Weapons and Laser Development Conference, January 18-19, Arlington, VA, 2006 |
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Abstract:
Not Available |
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Contributing Factors to Window Flashover Under Pulsed High Power Microwave Excitation at High Altitude |
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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 |
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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. |
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Dielectric Surface Flashover at Atmospheric Conditions under High Power Microwave Excitation |
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A. Neuber, “Dielectric Surface Flashover at Atmospheric Conditions under High Power Microwave Excitation,” APS conference, 2006 48th Annual Meeting of the Division of Plasma Physics, October 30-November 3, 2006, Meeting Id: DPP06, Philadelphia, PA. (invited) |
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Abstract:
Not Available |
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Dielectric Surface Flashover Research at Texas Tech University |
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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. |
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Abstract:
Not Available |
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Electro-explosive fuse development for helical flux compression generators |
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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 |
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Abstract:
Not Available |
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Helical Flux Compression Generator Non- Explosive Test Bed for Electro-Explosive Fuses |
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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. |
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Abstract:
Not Available |
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Interface Breakdown During High Power Microwave Transmission |
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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. |
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Abstract:
Not Available |
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Pressure Induced Conductivity for High Power Switching |
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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 |
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Abstract:
Summary form only given. Investigations of shock induced conductivity of non-crystalline insulators and crystalline semiconductors were performed. Although we measured the insulator-to-metallic state transition time and conductivity, the focus of this investigation was on the recovery phase of the induced conductivity (i.e. metallic-to-insulator state transition). The recovery time and shock conditions were measured with high speed electrical diagnostics. The goal of this research is to determine the feasibility of using shock induced conductivity as a means of producing a high power opening switch. To minimize switch losses, the insulator-to-metallic transition time and conductance is also important, but has been more widely studied. Initial impact studies have shown that certain insulator can be conductive for 100 microseconds and recover under modest voltage less than one microsecond using a ten gram explosive charge. Various shock intensities are used in the study. The shock is produced primarily with conventional commercial explosives. In addition, the impact of sample thickness and compression duration on the induced the conductivity were also studied. The correlation between modest voltage and high voltage recovery time and shut-off current were studied |
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Pulsed Unipolar Surface Flashover at Atmospheric Conditions |
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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 |
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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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Rapid Capacitor Chargers for Rep-Rated Operation of Low-Inductance Compact Marx Generators |
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Giesselmann, M.; McHale, B.; Neuber, A.;
Conference Record of the 2006 Twenty-Seventh International Power Modulator Symposium, 2006. 14-18 May 2006 Page(s):588 - 591 |
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Abstract:
We designed and tested several rapid capacitor chargers for rep-rated operation of low-inductance, compact Marx generators with rep-rates ranging from 10 Hz to 100 Hz. All chargers are designed to be packaged in cylindrical volumes with inside diameters in the range of 5 in-12 in. Our capacitor chargers are based on H-Bridge inverters using ultra fast 600 V class IGBTs. The high voltage is obtained by driving step-up transformers with nano-crystalline cores at 30 kHz. These chargers are capable of average DC output power levels of more than 5 kW for short time operation, during which the thermal inertia of the IGBT assembly provides effective cooling (up to seconds). To achieve reliable rep-rated operation of the chargers, we developed HV feedback sensors to monitor the charging process and solid state Marx-style trigger generators to command trigger the discharge of the main Marx |
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Surface Flashover under RF and Unipolar Excitation at Atmospheric Conditions |
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Krile, J.T.; Neuber, A.A.; Edmiston, G.F.; Krompholz, H.G.;
Conference Record of the 2006 Twenty-Seventh International Power Modulator Symposium, 2006. 14-18 May 2006 Page(s):7 - 12 |
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Abstract:
Flashover along insulators or insulating support structures has to be carefully addressed in the design of any DC, AC, or pulsed high voltage device. Although there is a large body of data on unipolar surface flashover in the atmosphere, which has led to empirical design rules primarily for the power distribution industry, the physics of the involved processes is widely unknown. The major limiting factor in the transmission of high power microwaves (HPM) into the atmosphere has been the vacuum-air interface. Both the unipolar and HPM surface flashover cases have been studied under vacuum conditions and have been found to have the same dominant mechanisms. Similarities between HPM window flashover on the air side and unipolar flashover are observed in an atmospheric environment as well |
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Transition of Window Breakdown from the Vacuum Multipactor Discharge to the Collisional RF Plasm |
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Kim, H.C.; Verboncoeur, J.P.; Edmiston, G.F.; Neuber, A.A.; Lau, Y.Y.; Gilgenbach, R.M.;
IEEE International Vacuum Electronics Conference, 2006 held Jointly with 2006 IEEE International Vacuum Electron Sources, 25-27 April 2006 Page(s):31 - 32 |
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Abstract:
In high-power microwave systems, we investigate the transition of breakdown from single surface vacuum multipactor discharge to collisional rf plasma in argon. As the gas pressure increases, electron-neutral collisions prevail against secondary electron emissions. In addition, the discharge formation time is obtained as a function of the gas pressure. |
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Ultrafast gas breakdown at pressures below one atmosphere |
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Krompholz, H.; Hatfield, L.; Neuber, A.; Chaparro, J.; Ryu, H.-Y.; Justis, W.;
2006 IEEE Conference on Electrical Insulation and Dielectric Phenomena, 15-18 Oct. 2006 Page(s):569 - 572 |
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Abstract:
Gas breakdown in quasi homogeneous electric fields with amplitudes of up to 3 MV/cm is investigated. The setup consists of a RADAN 303 A pulser and pulse sheer SN 4, an impedance-matched oil-filled coaxial line with a lens-transition to a biconical line in vacuum or gas, and an axial or radial gap with a width on the order of mm, with a symmetrical arrangement on the other side of the gap. Capacitive voltage dividers allow to determine voltage across as well as conduction current through the gap, with a temporal resolution determined by the oscilloscope sampling rate of 20 GS/s and an analog bandwidth of 6 GHz. The gap capacitance charging time and voltage risetime across the gap is less than 250 ps. Previous experiments at TTU with a slightly larger risetime have shown that breakdown is governed by runaway electrons, with multi-channel formation and high ionization and light emission in a thin cathode layer only. In argon and air, time constants for the discharge development have been observed to have a minimum of around 100 ps at several 10 torr. A qualitative understanding of the observed phenomena and their dependence on gas pressure is based on explosive field emission and gaseous ionization for electron runaway conditions. |
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Publication Year: 2005
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A Compact, Repetitive, 500kV, 500 J, Marx Generator |
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Neuber, A.A.; Chen, Y.J.; Dickens, J.C.; Kristiansen, M.;
2005 IEEE Pulsed Power Conference; June 2005 Page(s):1203 - 1206 |
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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 |
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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 |
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Abstract:
Not Available |
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Bubble Dynamics and Channel Formation for Cathode Initiated Discharges in Transformer Oil |
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Cevallos, M.; Butcher, M.; Dickens, J.; Neuber, A.; Krompholz, H.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):1235 - 1238 |
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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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Compact Pulsed Power at TTU |
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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. |
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Abstract:
Not Available |
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Composite Shadowgraphy and Luminosity Images of Self Breakdown Discharge Channels in Transformer Oil |
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Cevallos, M.; Butcher, M.; Dickens, J.; Neuber, A.; Krompholz, H.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):982 - 985 |
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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 |
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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) |
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Abstract:
Not Available |
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High Power Microwave Surface Flashover of a Gas-Dielectric Interface at 90 to 760 Tor |
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Edmiston, G.; Krile, J.; Neuber, A.; Dickens, J.; Krompholz, H.;
2005 IEEEPulsed Power Conference, June 2005 Page(s):350 - 353 |
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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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High Voltage Impulse Generator Using HV-IGBTs |
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Giesselmann, M.; Palmer, B.; Neuber, A.; Donlon, J.;
2005 IEEE Pulsed Power Conference, June 2005 Page(s):763 - 766, Monterey, California. |
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Abstract:
We are reporting on a High-Voltage Impulse Generator, which consists of a step-up transformer, which is driven by new HV-IGBTs (High-Voltage Isolated Gate Bipolar Transistors). The new HV-IGBTs are individually packaged silicon-dies intended for Pulsed-Power Applications. The silicon dies are normally packaged in large modules for locomotive motor drives and similar traction applications. In our work we used the Powerex QIS4506001 discrete IGBT and the QRS4506001 discrete diode, both with a nominal rating of 4500V/60A, derived from continuous-duty applications. Our experiments have shown that the devices are capable of handling currents in excess of 1 kA during pulsed operation. |
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Investigation of Charge Conduction and Self-Breakdown in Transformer Oil |
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Butcher, M.; Cevallos, M.; Neuber, A.; Krompholz, H.; Dickens, J.;
2005 IEEE Pulsed Power Conference, June 2005 Page(s):1143 - 1146 |
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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 |
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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 |
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Abstract:
Not Available |
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Multistage Helical Flux Compression Generator Non-Explosive Test Bed |
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Belt, D.; Dickens, J.; Mankowski, J.; Neuber, A.;
2005 IEEE Pulsed Power Conference, June 2005 Page(s):525 - 528 |
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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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Pulsed Dielectric Surface Flashover at Atmospheric Conditions |
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Morales, K.P.; Krile, J.T.; Neuber, A.A.; Krompholz, H.G.;
2005 IEEE Pulsed Power Conference, June 2005 Page(s):1147 - 1150 |
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Abstract:
Dielectric flashover along insulators in vacuum has been sufficiently researched in the past. Less studied, but of similar importance, is surface flashover at atmospheric pressures and the impact of various electrode geometries, humidity, and type of gas present. Previous research has shown distinct arc behavior in air and nitrogen for an electrode geometry in which the electric field lines curve above the dielectric surface. Specifically, flashover experiments in nitrogen have shown that the arc path will follow the electric field lines, not the dielectric surface. As a result, it was concluded that the arc development path, whether along the electric field line or the surface of the dielectric, is related to the oxygen content in the atmospheric background [1]. It is believed that this dependence is due to the arc's production of UV radiation in an oxygen rich environment. Further testing, in a pure nitrogen environment with UV illumination of the surface prior to the pulse application, has shown that UV plays a significant role in the arc development path. There is a near linear relationship between the percentage of liftoffs and the time delay between UV application and flashover. Additional studies have also shown a relationship between the UV intensity and the percentage of liftoffs. Based on these results we will discuss the physical mechanisms primarily involved in unipolar flashover at atmospheric pressure. Additional experimental results regarding the effects of humidity on the liftoff phenomenon will be presented as well. |
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Shock Induced Conductivity for High Power Switching |
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Veselka, H.; Neuber, A.; Dickens, J.;
2005 IEEE Pulsed Power Conference, June 2005 Page(s):734 - 737 |
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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 |
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Krile, J.; Edmiston, G.; Neuber, A.; Dickens, J.; Krompholz, H.;
2005 IEEE Pulsed Power Conference, June 2005 Page(s):354 - 357 |
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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 |
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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 |
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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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Subnanosecond Breakdown in Argon at High Overvoltages |
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Krompholz, H.; Hatfield, L.L.; Neuber, A.; Hemmert, D.; Kohl, K.; Chaparro, J.;
2005 IEEE Pulsed Power Conference, June 2005 Page(s):423 - 426 |
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Abstract:
Volume breakdown and surface flashover in quasi homogeneous applied fields in 10-5 to 600 torr argon are investigated, using voltage pulses with 150 ps risetime, < 1 ns duration, and up to 150 kV amplitude into a matched load. The test system consists of a transmission line, a transition to a biconical section, and a test gap, with gap distances of one to several mm. The arrangement on the other side of the gap is symmetrical. An improved system, with oil-filled transmission lines and lens between coax and biconical section to minimize pulse distortion, is being constructed. Diagnostics include fast capacitive voltage dividers, which allow to determine voltage waveforms in the gap, and conduction current waveforms through the gap. X-ray diagnostics uses a scintillator-photomultiplier combination with different absorber foils yielding coarse spectral resolution. Optical diagnostics to obtain information about the discharge channel dynamics is in preparation. Breakdown delay times, and e-folding time constants for the conduction current during the initial breakdown phase, are on the order of 100-400 ps, with minima in the range of several 10 torr. X-ray emission extends to pressures > 100 torr, indicating the role of runaway electrons during breakdown. Maximum x-ray emission coincides with fastest current risetimes at several 10 torr, which is probably related to an efficient feedback mechanism from gaseous amplification to field enhanced electron emission from the cathode. |
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Publication Year: 2004
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Compact FCG Driven Inductive Energy Storage System |
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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,. |
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Abstract:
Not Available |
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Compact Pulsed Power |
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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) |
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Abstract:
Not Available |
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Compact Pulsed Power |
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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) |
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Abstract:
Not Available |
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DC and Pulsed Dielectric Surface Flashover at Atmsopheric Pressure |
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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. |
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Abstract:
Not Available |
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Effect of temperature and pressure on DC pre-breakdown current in transformer oil |
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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 |
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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 |
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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 |
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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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Explosive Pulsed Power Sources for Directed Energy Weapons |
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A. Neuber, M. Giesselmann, "Explosive Pulsed Power Sources for Directed Energy Weapons”, invited presentation at the 2004 Directed Energy Symposium, Rockville, Maryland |
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Abstract:
Not Available |
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Fast Volume Breakdown in Argon and Air at Low Pressures |
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E. Crull, H. Krompholz, A. Neuber, and L. Hatfield, “Fast Volume Breakdown in Argon and Air at Low Pressures,” Euro Electromagnetics, Magdeburg, Germany, July 12-16, 2004. |
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Abstract:
Not Available |
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High Power Microwave Breakdown of a Gas-Dielectric Interface at 90 to 760 Torr |
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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 |
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Abstract:
Not Available |
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Light-matter interaction in transformer oil |
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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 |
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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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Nanosecond, optical diagnostics for liquid dielectric switches |
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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 |
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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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Pulsed gas breakdown with high overvoltages in argon and air |
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Crull, E.; Krompholz, H.; Neuber, A.; Hatfield, L.;
IEEE Conference Record - Abstracts. The 31st IEEE International Conference on Plasma Science, 2004. ICOPS 2004. 28 June-1 July 2004 Page(s):273 |
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Abstract:
Summary form only given. Fast gas breakdown with formative times in the sub-nanosecond regime is of interest for pulsed power switching and UWB applications. Use of coaxial transmission lines with conical sections connected to a test gap enables to apply fast voltage pulses to the gap, as well as the simultaneous measurement of voltage across and current through the gap. For small pulse amplitudes, with risetimes of 400 ps, a tip-plane geometry is used, with radii of curvature of 0.5 /spl mu/m. At pulse amplitudes of 5 kV, and macroscopic field enhancements on the order of 1000, delay times between current and voltage of less than 200 ps for pressures larger than 100 torr are observed, in both argon and dry air. Corresponding current risetimes I/(dI/dt) are less than 100 ps. Using a high voltage pulser (RADAN 303B with pulse slicer SN4, risetime 150 ps at 150 kV amplitude) enables the comparison of formative times for the tip-plane geometry with those of more homogeneous field distributions in the gap. |
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Unipolar Surface Flashover |
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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 |
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Abstract:
Not Available |
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Voltage-current characteristic of transformer oil under high electrical stress |
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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 |
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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
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Conductivity measurements of explosively shocked aluminum and OFHC copper used for armature material in a magnetic flux compression generator |
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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 |
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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 |
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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 |
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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 |
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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) |
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Abstract:
Not Available |
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Ferromagnetic and ferroelectric materials as seed sources for magnetic flux compressors |
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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 |
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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 |
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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) |
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Abstract:
Not Available |
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High Power Microwave Breakdown of Dielectric Interfaces |
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A. Neuber, “High Power Microwave Breakdown of Dielectric Interfaces,” invited talk at the Workshop on High Gradient RF, Argonne, IL, Oct. 7-9, 2003. |
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Abstract:
Not Available |
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Marx generator using pseudospark switches |
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Kuthi, A.; Alde, R.; Gundersen, M.; Neuber, A.;
Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 1, 15-18 June 2003 Page(s):241 - 244 Vol.1 |
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Abstract:
The design and preliminary operation of the major subsystems of a Marx style pulse generator using advanced pseudospark devices are presented. The bank consists of three 150 nF / 40 kV capacitors connected with three floating FS2000 type pseudospark switches. These switches can hold off 35 kV and pass up to 10 kA at repetition rates approaching 1 kHz. The expected lifetime of >200 kC and the relatively low housekeeping power of <50 W make the pseudospark switch an excellent candidate in compact Marx generator applications. Preliminary operation of the floating housekeeping units essential to the Marx generator is presented in deta |
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Nanosecond laser-triggered microwave switch |
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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 |
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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 |
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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 |
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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 |
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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 |
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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 |
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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 |
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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 |
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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 |
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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 |
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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 |
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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 |
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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 |
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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. |
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Self electrical breakdown in biodegradable oil |
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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 |
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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. |
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Short pulse electric field sterilization of liquid media |
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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 |
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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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Small sized MFCG for driving a high impedance load |
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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 |
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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. |
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Surface flashover across ceramic disks in vacuum at cryogenic temperatures |
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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 |
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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. |
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Publication Year: 2002
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All-Explosive Pulsed Power Generator System |
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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. |
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Abstract:
Not Available |
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Dependence of Flux Losses on MCG Helix Geometry |
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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. |
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Abstract:
Not Available |
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Electric breakdown in liquid nitrogen |
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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 |
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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. |
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Explosive-Driven Generation of Transient Antennas |
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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. |
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Abstract:
Not Available |
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Fast dielectric volume breakdown in liquid nitrogen |
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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 |
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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. |
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Feasibility study of an explosively formed transient antenna |
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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 |
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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. |
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Field enhanced microwave breakdown in gas for a plasma limiter |
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Hemmert, D.; Neuber, A.; Krompholz, H.; Mankowski, J.; Saeks, D.;
IEEE Conference Record - Abstracts. The 29th IEEE International Conference on Plasma Science, 2002. ICOPS 2002. 26-30 May 2002 Page(s):322 |
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Abstract:
Summary form only given, as follows. A new type of plasma limiter is being developed capable of turnon in less than 1 nsec. The approach taken is to initiate streamer breakdown via a micron radius needle tip. Studies were conducted on breakdown with a variety of gases at pressures from 10/sup 3/ to 10/sup -2/ torr. Gases tested included dry air, neon, argon, and krypton. Studies were also conducted on dc-voltage biasing the needle and its effect on breakdown. The experimental setup uses an S-band traveling wave resonant ring (TWRR) capable of power levels up to 100 MW when coupled to a 2.85 GHz, 4 MW, magnetron. High speed diagnostics with a response on the order of 1 ns record the microwave power, luminosity, and x-rays. A high speed CCD camera with an adjustable exposure time down to 10 nsec records a snapshot of the breakdown sequence. Preliminary results exhibit a reduction in expected gas breakdown levels by over two orders of magnitude. |
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Geometry Impact on Flux Losses in MFCGs |
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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. |
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Abstract:
Not Available |
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High Voltage, Sub Nanosecond Feedthrough Design for Liquid Breakdown Studies |
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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. |
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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 |
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Liquid Nitrogen As Fast High Voltage Switching Medium |
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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. |
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Abstract:
Not Available |
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Microwave breakdown studies of He-N² mixtures in a pillbox cavity from 760 to 3040 torr |
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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 |
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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. |
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Surface Flashover Across Ceramic Disks in Vacuum at Cryogenic Temperatures |
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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 |
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Abstract:
Not Available |
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Publication Year: 2001
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Advanced Modeling of an Exploding Flux Compression Generator using Lumped Element Models of Magnetic Diffusion |
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M. Giesselmann, T. Heeren, A. Neuber and M. Kristiansen, “Advanced Modeling of an Exploding Flux Compression Generator using Lumped Element Models of Magnetic Diffusion”, Proceedings of the 2001 Conference on Pulsed Power and Plasma Science, Las Vegas, Nevada, June 17-22, 2001, p. 162...165. |
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Abstract:
Not Available |
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Calculating stator losses in a helical MFCG |
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Benton, T.; Kuo-Ta Hsieh; Stefani, F.; Neuber, A.; Kristiansen, M.; Pulsed Power Plasma Science, 2001. PPPS-2001. Digest of Technical Papers
Volume 1, 17-22 June 2001 Page(s):85 - 89 vol.1 |
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Abstract:
This paper analyzes the transient electromagnetic, thermal, and structural behavior of the stator turns in a simple helical magnetic flux compression generator (MFCG). The main objective is to quantify the losses due to Ohmic heating and flux trapping in the conductors, including the effect of armature motion and armature proximity on the current distribution. The electric current excitation used in the modeling is based on experimental data from tests on a research MFCG. The electromagnetic (EM) and thermal analyses were conducted using EMAP3D, a 3D finite element analysis (FEA) code developed at The University of Texas at Austin (UT), which has the capability to model relative motion and sliding between conductors. Structural analyses were conducted using a version of DYNA3D that allows state data from EMAP3D to be used as input. Details of the analyses include temperature dependence on electrical, thermal, and mechanical properties. |
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Calculation of air temperature and pressure history during the operation of a flux compression generator |
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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 |
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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 |
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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 |
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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. |
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Conductivity measurements of MFCG armature material under shock and high strain rates utilizing a split-hopkinson pressure bar apparatus |
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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 |
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Abstract:
Not Available |
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Experimental and numerical investigation of armature/stator contact in magnetic flux compression generators |
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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 |
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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 |
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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 |
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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. |
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Experimental study of compact explosive-driven shock wave ferroelectric generators |
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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 |
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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 |
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High speed optical diagnostics of an exploding wire fuse for power conditioning of explosive flux compression generators |
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Giesselmann, M.; Heeren, T.; Neuber, A.; Walter, J.; Kristiansen, M.;
Digest of Technical Papers, Pulsed Power Plasma Science, 2001. PPPS-2001. Volume 1, 17-22 June 2001 Page(s):102 - 105 vol.1 |
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Abstract:
This paper presents high-speed optical diagnostics of an exploding wire fuse, which is used in the power conditioning system for an explosive flux compression generator. The images were taken using an IMACON(R) 790 high-speed framing camera utilizing a gated image intensifier tube. For the authors' measurements, the camera was operated in the high-speed multiple frame mode, yielding 8-10 sequential, 2 dimensional pictures with 100 ns between exposures. |
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Impact of helix geometry on MCG flux losses [magneto cumulative generators] |
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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 |
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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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Thermodynamic state of the magnetic flux compression generator volume |
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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 |
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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 |
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Transient Analysis of Copper Stator Turns in MFCG |
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T. Benton, K.-T. Hsieh, F. Stefani, A. Neuber, and M. Kristiansen, “Transient Analysis of Copper Stator Turns in MFCG,“ Paper No. H.06, International Conference on Pulsed Power Applications, Gelsenkirchen, March 29-30, 2001. |
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Abstract:
Not Available |
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Publication Year: 2000
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Dielectric/Gas Interface Breakdown Caused by High Power Microwave |
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D. Hemmert, A. Neuber, H. Krompholz, L.L. Hatfield, and M. Kristiansen, “Dielectric/Gas Interface Breakdown Caused by High Power Microwaves," Third Directed Energy Symposium, November 1-2, 2000, Albuquerque, New Mexico. |
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Abstract:
Not Available |
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Fundamental Studies of a Helical Magnetic Flux Compression Generator |
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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. |
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Abstract:
Not Available |
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Fundamental studies of a simple helical magnetic flux compression generator |
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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 |
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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 |
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Helical Flux Compression Generator for Basic Research |
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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. |
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Abstract:
Not Available |
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High Power Microwave Window Breakdown under Vacuum and Atmospheric Conditions |
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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. |
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Abstract:
Not Available |
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Pressure dependence of high power microwave solid dielectric/gas interface breakdown |
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Neuber, A.; Hemmert, D.; Krompholz, H.; Hatfield, L.L.; Kristiansen, M.;
2000. ICOPS 2000. IEEE Conference Record - Abstracts. The 27th IEEE International Conference on Plasma Science,
4-7 June 2000 Page(s):124 |
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Abstract:
The knowledge of the behavior of solid dielectric/gas interface breakdown caused by microwaves is crucial for developing new design methods for high power microwave windows. We investigate the physical mechanisms leading to breakdown for power levels on the order of 10 MW/cm2 at 2.85 GHz and gas pressures varying from 10-4 to 103 Torr. As an interface that is in widespread use, the focus was put on an alumina/air interface. Other gases are considered mainly for reference purposes. The high power microwaves are generated with a 4 MW magnetron having a 3.5 µs pulse width in conjunction with an S-band traveling wave resonator. This approach provides a power gain of maximum 25, sufficient to cause breakdown across the interface located in the pressure adjustable test region. The interface geometry comprises a thin ceramic alumina slab placed in the waveguide center. We ensure an almost purely tangential field and a localized breakdown by orienting the alumina slab normal to the direction of the wave propagation and making contact with two field enhancement tips placed in the middle of each waveguide broad wall |
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Studies on a Helical Magnetic Flux Compression Generator |
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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. |
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Abstract:
Not Available |
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Publication Year: 1999
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A theory of RF window failure |
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Valfells, A.; Ang, L.K.; Lau, Y.Y.; Gilgenbach, R.M.; Kishek, R.A.; Verboncoeur, J.; Neuber, A.; Krompholz, H.; Hatfield, L.L.; Plasma Science, 1999. ICOPS '99. IEEE Conference Record - Abstracts. 1999 IEEE International Conference on Plasma Science, 20-24 June 1999 Page(s):105 (Abstract only) |
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Abstract:
Summary form only given, as follows. We have recently developed a novel theory of multipactor discharge on a dielectric. The main results include the susceptibility diagram and the prediction that about one percent of the RF power is deposited to the dielectric surface over a wide range of conditions. In this paper, we extend the analysis to include the effects of outgassing and the subsequent ionization by the multipactoring electrons. This is an attempt to understand the final stage of dielectric failure that is initiated by multipactor. Similarities and differences in such failures, under RF and DC conditions, are explored. Analytic theory and simulation results will be presented and compared with experiments |
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Characterization of the power handling capability of an S-band double disc gas cooled microwave window |
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Neuber, A.; Ferguson, P.; Hendricks, K.; Hemmert, D.; 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):253 |
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Abstract:
Summary form only given. The S-Band double disc microwave window comprises a rectangular waveguide to circular pillbox transition with two separate high purity, TiN coated alumina discs brazed into the pillbox. The geometrical dimensions are optimized for minimum electromagnetic wave reflection at a microwave frequency of 2.85 GHz in TE10 mode. The window is designed for power levels up to a few 100 MW with several microseconds pulse duration. Crucial for the power handling capability is the gas species and pressure of the gas flow applied for cooling the alumina discs |
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Development of improved triggered vacuum switches |
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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 |
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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 |
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Influence of the microwave magnetic field on high power microwave window breakdown |
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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 |
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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 |
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Measurement of dynamic electrical conductivity of MFCG armature material under conditions of shock and high strain rate loading |
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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 |
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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 |
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Optical Diagnostics on Helical Flux Compression Generators |
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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) |
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Abstract:
Not Available |
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Surface flashover in liquid nitrogen |
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Butcher, M.; Neuber, A.; Krompholz, H.; Hatfield, L.L.;
1999 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, Volume 2, 17-20 Oct. 1999 Page(s):654 - 657 vol.2 |
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Abstract:
The use of cryogenic high voltage components to achieve higher energy densities is limited by virtually unknown insulator characteristics for cryogenic conditions. Using a fast coaxial setup, the flashover phenomena of dielectric test samples (Lexan, Alumina) immersed in liquid nitrogen are measured with optical and electrical diagnostics with nanosecond time resolution. The flashover voltage reaches a maximum of 30 kV for a 1.75 mm gap after 3 shots, and averages to about 10 kV after conditioning. Three phases in the discharge development can be distinguished: Phase 1 is a rapid current rise to the mA-regime, with several current spikes with amplitudes of less than 5 mA and durations of typically 20 ns. This phase lasts up to several 100 ns. Phase 2 is characterized by a rapid ionization with a current rise to the impedance limited value of several 100 A of phase 3 in a few nanoseconds. Waveforms of the luminosity follow the ones of the current in general. The physical mechanisms leading to this development, and the difference to the flashover phenomena in vacuum, are discussed qualitatively |
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Surface flashover of dielectrics immersed in super-cooled liquid nitrogen |
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Butcher, M.; Neuber, A.; Krompholz, H.; Hatfield, L.L.; Kristiansen, M.;
Digest of Technical Papers. 12th IEEE International Pulsed Power Conference, 1999. Volume 1, 27-30 June 1999 Page(s):450 - 453 vol.1 |
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Abstract:
In a fast coaxial setup, dielectric test sample and electrodes are immersed in super-cooled liquid nitrogen with a temperature near 68 K, and the flashover development process is characterized using fast optical and electrical diagnostics with nanosecond time resolution. The measured breakdown voltage as a function of consecutive flashover shots reaches its peak around the second flashover and declines to a constant value. This voltage is initially about 50% of the volume breakdown voltage in liquid nitrogen and drops to about 20% after the sample has been conditioned. Two materials, Lexan and alumina, were tested in the system and showed quite similar breakdown voltages, but alumina exhibited much more severe surface damage. The time resolved electrical diagnostic revealed three phases in the temporal development of the current. Phase 1 is a rapid rise to the mA regime that is probably associated with field emission. Phase 2 contains several pre-breakdown spikes with current amplitudes of less than 5 mA and duration of typically 20 nanoseconds that form and collapse over a period of tens to a couple hundred nanoseconds. Finally, Phase 3, is characterized by a rapid ionization across the surface with a current rise that covers 4 orders of magnitude in a few nanoseconds |
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The Role of Outgassing in Surface Flashover under Vacuum |
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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. |
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Abstract:
Not Available |
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Publication Year: 1998
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Breakdown of dielectric/vacuum interfaces caused by high power microwaves |
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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 |
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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 |
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Dielectric Surface Flashover in Vacuum at (100 K)) |
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A. Neuber, M. Butcher, H. Krompholz, and L. L. Hatfield: Dielectric Surface Flashover in Vacuum at (100 K). Proceedings of the XVIIIth International Symposium on Discharges and Insulation in Vacuum, Eindhoven (1998), Page(s): 815-818 |
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Abstract:
Not Available |
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Publication Year: 1997
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Dielectric surface flashover in vacuum at cryogenic temperature (100 K) |
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Neuber, A.; Krompholz, H.; Hatfield, L.L.;
1997. IEEE 1997 Annual Report of the Conference on Electrical Insulation and Dielectric Phenomena, Volume 2, 19-22 Oct. 1997 Page(s):575 - 578 |
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Abstract:
Recent developments in high power systems use cryogenic components, where the performance of insulators at such low temperatures is unknown. In a fast coaxial setup, electrodes and dielectric sample are cooled to less than 100 K in vacuum, and the flashover initiation processes for gap distances on the order of 1 cm are characterized using fast electrical and optical diagnostics. As reported before, two development stages can be distinguished: a first phase with slowly rising current and the presence of free electrons, with a duration of 10-50 ns, and a second stage with a fast current rise due to gaseous ionization and collision dominated electrons. First experiments comparing cooled samples and samples at room temperature do not show discernible differences for Lexan. For Alumina, however, an increase of the duration of phase 1 is observed, with a higher current amplitude at the transition from phase one to phase two. Also, the current rise in phase two is reduced. These results indicate a temperature dependence of the electron induced outgassing process which is expected to cause the transition from phase one to phase two |
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Window and Cavity Breakdown caused by High Power Microwaves |
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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) |
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Abstract:
Not Available |
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Window and Cavity Breakdown caused by High Power Microwaves |
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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) |
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Abstract:
Not Available |
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Window and Cavity Breakdown caused by High Power Microwaves |
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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) |
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Abstract:
Not Available |
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Book
Publication Year: 2007
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Pulsed Gas Breakdown With High Overvoltages in Argon and Air |
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E. Crull, H. Krompholz, A. Neuber, and L. Hatfield, "Pulsed Gas Breakdown With High Overvoltages in Argon and Air", Ultra-Wideband Short-Pulse Electromagnetics 7, F. Sabbath, Ed., Springer, NY, 2007, Page(s) 409-414. |
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Abstract:
Not Available |
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Publication Year: 2005
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Basic Physics, In: Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generator |
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B. L. Freeman, and A. Neuber, “Basic Physics,” In: Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generator, A. Neuber Edtr., Springer Berlin Heidelberg New York, ISBN 3-540-26051-X, 2005. |
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Abstract:
Not Available |
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Chapter 6, Generator Modeling, Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generators |
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Michael Giesselmann, Ivor R. Smith, Bucur M. Novac and Andreas Neuber, Chapter 6, Generator Modeling, "Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generators", Springer, Berlin, Heidelberg, New York, ISBN-13 978-3-540-26051-6. |
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Abstract:
Not Available |
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Chapter 7, Power Conditioning, "Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generators |
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Tammo Heeren, Michael Giesselmann, and Andreas Neuber, Chapter 7, Power Conditioning, "Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generators", Springer, Berlin, Heidelberg, New York, ISBN-13 978-3-540-26051-6. |
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Abstract:
Not Available |
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FCG Overview, In: Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generator |
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B. L. Freeman, and A. Neuber, “FCG Overview,” In: Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generator, A. Neuber Edtr., Springer Berlin Heidelberg New York, ISBN 3-540-26051-X, 2005. |
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Abstract:
Not Available |
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Generator Modeling, In: Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generator |
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M. Giesselmann, I. R. Smith, B. M. Novac, and A. Neuber, “Generator Modeling,” In: Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generator, A. Neuber Edtr., Springer Berlin Heidelberg New York, ISBN 3-540-26051-X, 2005. |
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Abstract:
Not Available |
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Loss Mechanism Basics, In: Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generator |
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B. L. Freeman, and A. Neuber, “Loss Mechanism Basics,” In: Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generator, A. Neuber Edtr., Springer Berlin Heidelberg New York, ISBN 3-540-26051-X, 2005. |
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Abstract:
Not Available |
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Power Conditioning, In: Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generator |
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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. |
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Abstract:
Not Available |
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Practical FCG Pulsed Power System, In: Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generator |
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A. Neuber and Juan-Carlos Hernandez, “Practical FCG Pulsed Power System,” In: Explosively Driven Pulsed Power, Helical Magnetic Flux Compression Generator, A. Neuber Edtr., Springer Berlin Heidelberg New York, ISBN 3-540-26051-X, 2005. |
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Abstract:
Not Available |
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Publication Year: 2001
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Windows and RF Breakdown |
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A. Neuber, L. Laurent, Y. Y. Lau, and H. Krompholz, “Windows and RF Breakdown,” Chapter 10 (pages 325-375) in High-Power Microwave Sources and Technologies, R. J. Barker and E. Schamiloglu, Editors, IEEE Press 2001, ISBN 0.7803-6006-0. |
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Abstract:
Not Available |
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