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

John Jerome Mankowski, Ph.D., PE

Contact Information

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

Phone: (806)742-0526
Fax: (806)742-1281
john.mankowski@ttu.edu

Education

Research Interests

Awards and Professional Societies

Licensing

Publications


Journal

Publication Year:  2008
+ Compact Electro-Explosive Fuses for Explosive Driven Pulsed Power
  D. R. McCauley, D. W. Belt, J. J. Mankowski, J. C. Dickens, A. A. Neuber, and M. Kristiansen, "Compact Electro-Explosive Fuses for Explosive Driven Pulsed Power", to appear in IEEE Transactions on Plasma Science (2008)
Abstract:  Not Available
+ Imaging of the Explosive Emission Cathode Plasma in a Vircator High-Power Microwave Source
  Walter, J.; Mankowski, J.; Dickens, J.; Imaging of the Explosive Emission Cathode Plasma in a Vircator High-Power Microwave Source; Plasma Science, IEEE Transactions on Volume 36, Issue 4, Part 1, Aug. 2008 Page(s):1388 - 1389 Digital Object Identifier 10.1109/TPS.2008.924489
Abstract:  Not Available
+ Low-Jitter Triggered Spark Gap With High-Pressure Gas Mixtures
  Yeong-Jer Chen; Mankowski, J.J.; Dickens, J.C.; Walter, J.; Kristiansen, M.; Low-Jitter Triggered Spark Gap With High-Pressure Gas Mixtures; Plasma Science, IEEE Transactions on Volume 36, Issue 5, Part 3, Oct. 2008 Page(s):2546 - 2553 ; Digital Object Identifier 10.1109/TPS.2008.2004366
Abstract:  Not Available
+ Secondary Arc Formation Within a Distributed Energy Railgun
  Karhi, R.W.; Mankowski, J.J.; Dickens, J.C.; Kristiansen, M.; Wetz, D.A.; Secondary Arc Formation Within a Distributed Energy Railgun; Plasma Science, IEEE Transactions on Volume 36, Issue 5, Part 3, Oct. 2008 Page(s):2738 - 2746 Digital Object Identifier 10.1109/TPS.2008.2004228
Abstract:  Not Available
+ Utilization of a Nonexplosive Test Bed for Flux-Compression-Generator Electroexplosive Opening Switches
  D. W. Belt, J. J. Mankowski, A. A. Neuber, J.C. Dickens, M. Kristiansen, Utilization of a Nonexplosive Test Bed for Flux-Compression-Generator Electroexplosive Opening Switches, IEEE Transactions on Plasma Science 36, 2684 - 2690, (2008).
Abstract:  Not Available
Publication Year:  2007
+ A Bench Top Railgun With Distributed Energy Sources
  Mankowski, J.; Dickens, J.; Giesselmann, M.; McDaniel, B.; McHale, B.; Kristiansen, M.; IEEE Transactions on Magnetics, Volume 43, Issue 1, Part 2, Jan. 2007 Page(s):167 - 169
Abstract:  Experimental results of a distributed energy source railgun are presented. Distributed energy source railguns were first proposed by Marshal in an asynchronous scheme and later by Parker synchronously. Both schemes employ a "traveling excitation wave" to push the projectile along the rail. The primary advantages of such a scheme over the common breech-fed is higher efficiency due to less energy remaining in the rail and lower rail resistive loses. Another advantage is the reduction in the probability of re-strike. However, these advantages are achieved at a cost of higher switching complexity. As a proof of principle experiment, we have constructed a bench-top solid armature railgun with distributed energy sources. Instead of a single, capacitive, breech-fed, energy source, the current is supplied by two storage capacitor banks, placed at different positions along the rail. The switching configuration, which requires a dedicated switch at each capacitor, is realized with sold state switches. The railgun is diagnosed in order to evaluate performance and to appropriately trigger the switches. In addition, experimental results are compared to simulation

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

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+ Jitter and Recovery Rate of a Triggered Spark Gap with High Pressure Gas Mixtures
  Yeong-Jer Chen; Mankowski, J.J.; Walter, J.W.; Dickens, J.C.; Jitter and Recovery Rate of a Triggered Spark Gap with High Pressure Gas Mixtures; Pulsed Power Plasma Science, 2007. PPPS 2007. Conference Record - Abstracts. IEEE 17-22 June 2007 Page(s):255 - 25
Abstract:  Summary form only given. Recent attention in impulse antenna phased array has necessitated the need to develop a reliable high voltage, high repetition rate switch that will operate with ultra low jitter. An ideal jitter of a small fraction of the rise time is required to accurately synchronize the array to steer and preserve the rise time of the radiated pulse. This paper presents the impact, gases and gas mixtures have on switch performance which includes recovery rate and in particular, jitter. A 50 Omega, 2.4 nF pulse forming line is charged to 50 kV and provides the low inductance voltage source to test the different gases. Triggering is provided by an SOS voltage source that supplies >100 kV, 10 ns rise-time pulses at a rep rate up to 1 kHz in burst mode. A hermetically sealed spark gap with a Kel-F lining is used to house the switch and high pressure gas. The system will also introduce a high pressure gas mixing chamber that can mix various gases up to 2000 psi. Gases tested include dry air, H2, and SF6.

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Publication Year:  2006
+ Design and implementation of a flux compression generator nonexplosive test bed for electroexplosive fuses
  D. Belt, J. Mankowski, A. Neuber, J. Dickens, and M. Kristiansen Center for Pulsed Power and Power Electronics, Texas Tech University, Lubbock, Texas 79409-3102; Departments of Electrical, Texas Tech University, Lubbock, Texas 79409-3102; and Computer Engineering and Physics, Texas Tech University, Lubbock, Texas 79409-3102 Review of Scientific Instruments, Vol 77, Article 094702 (2006) (7 pages)
Abstract:  Helical flux compression generators (HFCGs) of a 50 mm form factor have been shown to produce output energies on the order of ten times the seeded value and a typical deposited energy of 3 kJ into a 3 µH inductor. By utilizing an electroexplosive fuse, a large dI/dt into a coupled load is possible. Our previous work with a nonoptimized fuse has produced ~100 kV into a 15 load, which leads into a regime relevant for high power microwave systems. It is expected that ~300 kV can be achieved with the present two-stage HFCG driving an inductive storage system with electroexploding fuse. In order to optimize the electroexplosive wire fuse, we have constructed a nonexplosive test bed which simulates the HFCG output with high accuracy. We have designed and implemented a capacitor based, magnetic switching scheme to generate the near exponential rise of the HFCG. The varying inductance approach utilizes four stages of inductance change and is based upon a piecewise linear regression model of the HFCG wave form. The nonexplosive test bed will provide a more efficient method of component testing and has demonstrated positive initial fuse results. By utilizing the nonexplosive test bed, we hope to reduce the physical size of the inductive energy storage system and fuse substantially. ©2006 American Institute of Physics

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+ The Impact of Field Enhancements and Charge Injection on the Pulsed Breakdown Strength of Water
  Wetz, D.A.; Mankowski, J.J.; Dickens, J.C.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 34, Issue 5, Part 1, Oct. 2006 Page(s):1670 - 1679
Abstract:  A unique theoretical model of the breakdown mechanism in water has been developed and further tested in both simulation software and experimentation. The conducted experiments test the degree to which electrode material, surface roughness, and surface area impact the dielectric strength of water. Voltage pulses with respective rise times of roughly 200 and 20 ns were applied to a water test gap producing electric fields in excess of 1.5 MV/cm. In experiments testing various electrode materials, thin film coatings of various metallic alloys and oxides were applied to Bruce-profiled stainless steel electrodes, with an effective area of 5$hboxcm^2$, through ion beam deposition. Similar Bruceprofiled stainless steel electrodes with surface roughness ranging from 0.26 to 1.96$muhboxm$and effective areas ranging from 0.5 to 75$hboxcm^2$were used in the study of surface roughness and area. Additionally, shadowgraph images of a point plane geometry were taken to further understand the breakdown processes that occur.

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Publication Year:  2005
+ Design and optimization of a compact, repetitive, high-power microwave system
  Y. J. Chen, A. A. Neuber, J. Mankowski, J. C. Dickens, and M. Kristiansen Texas Tech University, Center for Pulsed Power and Power Electronics, Lubbock, Texas 79409-3102 R. Gale Texas Tech University, Nano Tech Center, Lubbock, Texas 79409-3102 Review of Scientific Instruments, Vol 76, Article 104703 (2005) (8 pages)
Abstract:  The electrical characteristics and design features of a low inductance, compact, 500 kV, 500 J, 10 Hz repetition rate Marx generator for driving an high-power microwave (HPM) source are discussed. Benefiting from the large energy density of mica capacitors, four mica capacitors were utilized in parallel per stage, keeping the parasitic inductance per stage low. Including the spark-gap switches, a stage inductance of 55 nH was measured, which translates with 100 nF capacitance per stage to ~18.5 characteristic Marx impedance. Using solely inductors, ~1 mH each, as charging elements instead of resistors enabled charging the Marx within less than 100 ms with little charging losses. The pulse width of the Marx into a matched resistive load is about 200 ns with 50 ns rise time. Repetitive HPM generation with the Marx directly driving a small virtual cathode oscilator (Vircator) has been verified. The Marx is fitted into a tube with 30 cm diameter and a total length of 0.7 m. We discuss the Marx operation at up to 21 kV charging voltage per stage, with repetition rates of up to 10 Hz in burst mode, primarily into resistive loads. A lumped circuit description of the Marx is also given, closely matching the experimental results. Design and testing of a low cost, all-metal Vircator cathode will also be discussed. ©2005 American Institute of Physics

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+ The Impact of Surface Conditioning and Area on the Pulsed Breakdown Strength of Water
  Wetz, D.A., Jr.; Truman, K.P.; Mankowski, J.J.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 33, Issue 4, Part 1, Aug. 2005 Page(s):1161 - 1169
Abstract:  Experimental results are presented on the degree to which electrode surface conditioning and surface area impact the dielectric strength of water. The applied pulse to the test gap reached electric field levels greater than 1.5 MV/cm with risetimes around 200 and 50 ns, respectively. The test gap is composed of 304 stainless steel electrodes machined with a Bruce profile. Electrode surface roughness ranged from 0.34 to 1.41$muhbox m$and effective areas ranged from 0.5 to 75$hbox cm^2$. Additional results are presented on the pulsed breakdown strength of Rexolite with various surface finishes ranging from .025 to 5.715$muhbox m$. Conclusions are made as to the effect electrode surface area and surface roughness has on the holdoff voltage of water dielectric systems. Conclusions are also made as to the impact of the surface condition of Rexolite has on its bulk breakdown strength.

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

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+ Microwave frequency determination mechanisms in a coaxial vircator
  Xupeng Chen; Dickens, J.; Mankowski, J.; Hatfield, L.L.; Eun Ha Choi; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 32, Issue 5, Part 1, Oct. 2004 Page(s):1799 - 1804
Abstract:  Traditionally, the radiated microwave frequency in a coaxial vircator is considered to be determined primarily by the virtual cathode oscillation frequency and the electron reflection frequency. In this paper, some experiments showing different results are reported. In particular, the E-beam is observed to play an important role in the cavity formation. Some possible explanations, including a virtual cavity concept, are proposed. The cavity resonance effect on a coaxial virtual cathode oscillator with different geometries has been investigated in detail. Investigation of the E-beam performance will improve understanding of the interaction between the E-beam and microwaves, which is a key for determining the microwave frequency. These results are helpful in optimizing the design of a cylindrical diode to avoid microwave frequency shifting and mode competition.

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Publication Year:  2003
+ Efficiency results from a coaxial vircator using a simple feedback technique
  Mankowski, J.; Cheng, X.; Dickens, J.; Kritiansen, M.; Choi, E.; Digest of Technical Papers. PPC-2003. 14th IEEE International Pulsed Power Conference, 2003. Volume 1, 15-18 June 2003 Page(s):455 - 458 Vol.1
Abstract:  Experimental findings on the coaxial virtual cathode oscillator (vircator) at Texas Tech University are reported. A major modification to the system extended the pulse forming line several meters. The pulsed power system now delivers up to 750 kV and 60 kA for at least 70 nsec. Additional modifications include diagnostics to measure the diode voltage, current, and radiated field pattern of the output microwaves. In this initial phase of experiments copper reflectors were installed within the diode to provide a simple means of microwave feedback to assist in the e-beam modulation. Thus far we have observed microwave peak power output with feedback reflectors as high as 3.5 GW corresponding to an efficiency of /spl sim/9.5%. Measured radiated field patterns show evidence of multimode operation.

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

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+ Subnanosecond corona inception in an ultrawideband environment
  Mankowski, J.; Dickens, J.; Kristiansen, M.; Lehr, J.; Prather, W.; Gaudet, J.; IEEE Transactions on Plasma Science, Volume 30, Issue 3, Part 1, June 2002 Page(s):1211 - 1214
Abstract:  Corona discharges in ultrawideband radiating systems can have adverse effects on performance such as reflection, phase dispersion, and significant power losses. A test-bed has been assembled to experimentally observe corona created by voltage pulses similar to ultrawideband systems. The current work involves the attenuation of an incident pulse after propagation through a self-initiated corona and relative measurements of visible light emission from the photoionization produced during streamer development. Several gas dielectrics, including ambient air, N/sub 2/, H/sub 2/, and SF/sub 6/, were tested.

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Publication Year:  2000
+ A review of short pulse generator technology
  Mankowski, J.; Kristiansen, M.; IEEE Transactions on Plasma Science, Volume 28, Issue 1, Feb. 2000 Page(s):102 - 108
Abstract:  Today's ultrafast, pulse generators are capable of producing high-voltage pulses, (>1 kV), with fast, leading-edge rise times, (<1 ns). A review of generator implementation methods is presented that includes a detailed discussion of the various circuit designs and a list of commercially available high-voltage pulse generators. All of these generators are capable of rise times less than a few ns and voltages greater than several hundred volts. Finally, a brief description of the three primary switch types, reed, spark gap, and solid state is presented

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

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Conference Paper/Presentation

Publication Year:  2008
+ A 50 kV, 100 Hz Low Jitter Triggered Spark Gap with High Pressure Gas Mixtures
  Chen, Yeong-Jer; Mankowski, John J.; Dickens, James C.; Walter, John; Kristiansen, Magne; A 50 kV, 100 Hz Low Jitter Triggered Spark Gap with High Pressure Gas Mixtures; IEEE International Power Modulators and High Voltage Conference, Proceedings of the 2008; 27-31 May 2008 Page(s):197 - 200; Digital Object Identifier 10.1109/IPMC.2008.4743614
Abstract:  Not Available
+ Analysis of Mesoband Single Element Pulsed Ring-Down Antennas for Implementation in Phased Array Systems
  Belt, D.; Mankowski, J.; Walter, J.; Dickens, J.; Kristiansen, M.; IEEE International Power Modulators and High Voltage Conference, Proceedings of the 2008 27-31 May 2008 Page(s):152 - 155 Digital Object Identifier 10.1109/IPMC.2008.4743602
Abstract:  Not Available
+ Jitter and recovery rate of a 50 kV, 100 Hz triggered spark gap with high pressure gas mixtures
  Yeong-Jer Chen; Mankowski, J.J.; Walter, J.W.; Dickens, J.C.; Jitter and recovery rate of a 50 kV, 100 Hz triggered spark gap with high pressure gas mixtures; Plasma Science, 2008. ICOPS 2008. IEEE 35th International Conference on 15-19 June 2008 Page(s):1 - 1 Digital Object Identifier 10.1109/PLASMA.2008.4590809
Abstract:  Not Available
Publication Year:  2007
+ Electro-Explosive Fuse Optimization for Helical Flux Compression Generator Using a Non-Explosive Test Bed
  D. McCauley, D. Belt, J. Mankowski, J. Dickens, A. Neuber, M. Kristiansen, "Electro-Explosive Fuse Optimization for Helical Flux Compression Generator Using a Non-Explosive Test Bed," presented at the 2007 IEEE Pulsed Power and Plasma Science Conference, Albuquerque, NM June 17-22, 2007.
Abstract:  Helical Flux Compression Generators (HFCG) of 50 mm form factor have been shown to produce a maximum energy deposit of 3 kJ into a 3 muH inductor from a seed current. A large dl/dt into a coupled load is possible when an electro-explosive fuse is used. Previous work with a non-optimized fuse has produced ~100 kV into a 15Omega load which leads into a regime relevant for High Power Microwave (HPM) systems. It is expected that ~3()0kV can be achieved with the present 2 stage HFCG driving an inductive storage system with an electro-exploding fuse. In order to optimize the electro-explosive fuse design, a non-explosive test bed, which closely simulates the 45 kA HFCG output, is used. To optimize the tiise, effects of fuse material, fuse length, and fuse shape will be examined as well as the effects of various quenching materials. Our previous work has characterized fuse material but we are also looking into the effects of the processes used to create the fuse wire, such as tempered wire versus fully annealed wire. Additionally, to maximize the output voltage and minimize the fuse recovery time, we are optimizing the length of the fuse wire. For shorter fuse lengths, we are optimizing fuse shape as well as fuse length to find the best fuse recovery time. By optimizing the individual parameters of an electro-explosive fuse, the fuse as a whole will be optimized to produce maximum output voltage when used with an HFCG.

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

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

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

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+ Electro-explosive fuse development for helical flux compression generators
  D. Belt, J. Dickens, J. Mankowski, A. Neuber, and M. Kristiansen, “Electro-explosive fuse development for helical flux compression generators,” presented at the 2006 International Conference on Megagauss Magnetic Field Generation and Related Topics, November 5-10, 2006 Santa Fe, New Mexico, USA
Abstract:  Not Available
+ Helical Flux Compression Generator Non- Explosive Test Bed for Electro-Explosive Fuses
  D. Belt, J. Dickens, J. Mankowski, A. Neuber, M. Kristiansen, “Helical Flux Compression Generator Non- Explosive Test Bed for Electro-Explosive Fuses”, presented at the 27th Power Modulator Symposium and 2006 High Voltage Workshop May 14-18, 2006, Washington, DC.
Abstract:  Not Available
+ The Impact of Water Conductivity, Electrode Material, and Electrode Surface Roughness on the Pulsed Breakdown Strength of Water
  Wetz, D.; Mankowski, J.; McCauley, D.; Dickens, J.; Kristiansen, M.; Conference Record of the 2006 Twenty-Seventh International Power Modulator Symposium, 2006. 14-18 May 2006 Page(s):104 - 107
Abstract:  Experimental results are presented on the impact water conductivity, electrode material, and electrode surface roughness have on the dielectric strength of water. A 2 mm water gap was tested under pulsed conditions with maximum electric fields in excess of 1.5 MV/cm. Bruce profiled electrodes manufactured from various materials including molybdenum, aluminum, copper, tungsten, nickel, stainless steel, and zinc oxide, which have work functions ranging from 4.2 eV to 5.3 eV, have been tested. The roughness average of the various surfaces was varied from 0.1 mum to 1.96 mum and the conductivity of the water within the gap was varied from 1muS/cm to 39 muS/cm to determine the impact each has when tested in combination with the various electrode materials and surface roughnesses. Conclusions are made as to the effect each of these factors has on the holdoff strength of a water dielectric system

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+ Virtual Cathode Oscillator Component Optimization
  Chen, Y.-J.; Mankowski, J.; Walter, J.; Kristiansen, M.; Conference Record of the 2006 Twenty-Seventh International Power Modulator Symposium, 2006. 14-18 May 2006 Page(s):157 - 160
Abstract:  Recent research efforts at TTU include a simple aluminum cathode for E-beam generation in a virtual cathode oscillator (vircator). As a continuation of these results, we are fabricating and testing several different types of cathodes for the vircator driven by a Marx generator and a pulse forming line (400 kV, 60 ns, 30 Omega). The cathodes, each with an emitting area of ~32 cm2, are made from aluminum and oxygen free copper fashioned to similar geometries with either a chemical etch or a CNC machine process. The vircator is tested with all of these cathodes and evaluated for beam voltage, current, and HPM generation. In addition to the cathode testing, several stainless steel and tungsten anode meshes with varying transparencies (50%-80%) are evaluated

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Publication Year:  2005
+ A Low-Cost Metallic Cathode for a Vircator HPM Source
  Mankowski, J.; Chen, Y.; Dickens, J.; Neuber, A.; Gale, R.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):66 - 69
Abstract:  Recent research efforts at TTU include the testing of a rapidly charged, rep-rated Marx generator driving a reflex triode vircator [1]. As expected, the burning of the cathode material (ordinary cloth velvet), was the primary failure mechanism during repetitive operation. In an effort to achieve a repetitive vircator (>10 Hz), we are exploring a low-cost, all-metal cathode. The cathode is made from aluminum with a patterned surface. A typical pattern is composed of peaks and troughs with dimensions on the order of tens of microns. The pattern is achieved with a simple, low-cost chemical etching process. Results include current, voltage, and microwave waveforms from two solid metal cathodes and a cloth velvet cathode.

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+ A Low-Cost Metallic Cathode for a Vircator HPM Source
  Y.J. Chen, J.J. Mankowski, A. Neuber, J.C. Dickens, “A Low-Cost Metallic Cathode for a Vircator HPM Source,” Proceedings of the 15th Int. IEEE Pulsed Power Conference, pp. 66-69, Monterey, CA, June 13-17, 2005
Abstract:  Not Available
+ An Ion Beam Sputtering System for Electrode Surface Conditioning
  Wetz, D.; Mankowski, J.; Kristiansen, M.; IEEE Conference Record - Abstracts. IEEE International Conference on Plasma Science, 2005. ICOPS '05. 20-23 June 2005 Page(s):123 - 123
Abstract:  Summary form only given. In the past there has been considerable research performed using electromagnetic plasma thrusters as the primary ion source in sputtering applications. In the experiments conducted here, thin film coatings of various hard metallic alloys and oxides were applied to stainless steel electrodes using ion beam deposition. An SPT type Hall effect thruster capable of producing an ion beam with energies between 150 eV and 350 eV was used as the deposition ion source. The surface coatings were applied to Bruce profiled stainless steel electrodes which have an effective surface area of 5 cm2 and a roughness average of roughly 70 nm. The electrodes were then examined using an optical profiler to accurately measure the roughness average of the thin film coating as well as the effective layer thickness. A comparison of the results obtained from each surface material is performed

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+ Multi-Frequency and Multi-Mode Microwave Identification in a Vircator Research
  Xupeng Chen; Dickens, J.C.; Hatfield, L.L.; Mankowski, J.; Kristiansen, M.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):190 - 193
Abstract:  In virtual cathode oscillator (VIRCATOR) research, multi-frequency and multi-mode microwaves are coupled out and propagate along a waveguide. Identifying the microwave propagating modes has become a priority work for further research on microwave radiation physical mechanisms. Generally, an antenna matrix at the end of an open waveguide, which can shape the radiated microwave power distribution, is used to identify the microwave propagating modes [1-2]. Actual microwave radiation mechanisms in a VIRCATOR are complicated. Multi propagating modes and multifrequency microwaves coexist simultaneously, which challenges the antenna matrix method. In this paper, based on microwave propagating theory in a waveguide, a new method is proposed to identify multi-frequency and multi-mode microwaves, which is partially justified by the experimental data at Texas Tech University.

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

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+ The Impact of Electrode Area and Surface Roughness on the Pulsed Breakdown Strength Water
  Wetz, D.; Mankowski, J.; Kristiansen, M.; 2005 IEEE Pulsed Power Conference, June 2005 Page(s):1163 - 1166
Abstract:  Experimental results are presented on the degree to which electrode surface area and surface roughness impacts the dielectric strength of water. A 2 mm water gap was tested under pulsed conditions with maximum electric fields in excess of 1 MV/cm and maximum currents of more than 5 kA. Six different pairs of stainless steel electrodes, each having a unique Bruce profile and thus a different effective surface area, were used to achieve a uniform electric field across the gap. The differing electrode pair profiles, with effective areas ranging from 0.5 cm2 to 76 cm2, were designed to minimize the change in gap capacitance. Prior to each test, a different roughness average, ranging from 0.26 ¿m to 1.96 ¿m, was applied to the electrodes. Conclusions are made as to the effect both electrode surface area and surface roughness has on the holdoff voltage of water dielectric systems. In addition, shadowgraph images of pre-breakdown events are presented.

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

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Publication Year:  2004
+ Compact Pulsed Power
  M. Kristiansen, J. Dickens, H. Krompholz, M. Giesselmann, A. Neuber, J. Mankowski, L. Hatfield, “Compact Pulsed Power,“ Proceedings of the 5th International Symposium on Pulsed Power and Plasma Applications, Oct. 18-20, Chan-Won, Korea, p. 10-15, 2004. (Invited paper)
Abstract:  Not Available
+ Impact of surface conditioning of large area electrodes on the dielectric strength of water
  Wetz, D.; Mankowski, J.; Truman, K.; Kristiansen, M.; Conference Record of the Twenty-Sixth International Power Modulator Symposium, 2004 and 2004 High-Voltage Workshop. 23-26 May 2004 Page(s):512 - 515
Abstract:  Experimental results are presented on the impact electrode material and surface treatment has on the dielectric strength of water. A 4 mm water gap was tested under pulsed conditions with pulse widths greater than 1 /spl mu/s, peak electric fields over 2 MV/cm and peak currents over 15 kA. 304 stainless steel electrodes machined with a Bruce profile and an effective area of 5 cm/sup 2/ were tested with surface roughnesses ranging from .34 /spl mu/m to 1.41 /spl mu/m. Results comparing electrodes that have additionally been electropolished are compared to those without an additional treatment. These various surface treatments remove microprotrusions from the electrode's surface which reduce field enhancements across the electrode surface. It is believed that this technique will minimize the number of breakdown initiation points thereby increasing the dielectric strength. Results are given on the degree to which each finish improves the dielectric strength of water.

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+ The effect of area on pulsed breakdown in water
  Truman, K.; Mankowski, J.; Wetz, D.; Kristiansen, M.; Conference Record of the Twenty-Sixth International Power Modulator Symposium, 2004 and 2004 High-Voltage Workshop. 23-26 May 2004 Page(s):126 - 128
Abstract:  Experimental results are presented on the degree to which electrode surface area impacts the dielectric strength of water. A water gap of 4 mm was tested under pulsed conditions with a maximum electric field in excess of 1 MV/cm and a maximum current of more than 20 kA. Stainless steel electrodes with a Bruce profile were used to generate a uniform electric field across the water gap. The profile of the electrodes enabled effective areas ranging from 0.5 cm/sup 2/ to 75 cm/sup 2/ while minimizing the change in capacitance of the water gap. Conclusions are made as to the effect electrode surface area has on the holdoff voltage and holdoff time of water dielectric systems.

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

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

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+ Experimental results of a 2 GW vircator
  Mankowski, J.J.; Choi, E.H.; Dickens, J.C.; Xupeng Chen; Kristiansen, M.; IEEE Conference Record - Abstracts. The 30th International Conference on Plasma Science, 2003. ICOPS 2003. 2-5 June 2003 Page(s):187
Abstract:  Summary form only given. Experimental findings on the coaxial virtual cathode oscillator (vircator) at Texas Tech University are reported. Recent modifications to the system include extending the pulse forming line that now provides an applied diode voltage of 600 kV for 70 nanoseconds at 60 kA. Other modifications include diode voltage, current, and radiated field diagnostics. In this initial phase of experiments, copper reflectors were installed within the diode to provide a simple means of microwave feedback to assist in the e-beam modulation. Thus far we have observed microwave peak power output with feedback reflectors as high as 2 GW corresponding to an efficiency of -6%. The mode observed at these high efficiencies is almost entirely TE/sub 11/. At lower efficiencies, both TM/sub 01/, and TE/sub 11/ modes are observed. These results suggest mode competition at lower efficiencies.

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

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

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Publication Year:  2002
+ Field enhanced microwave breakdown in gas for a plasma limiter
  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
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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Publication Year:  2001
+ Gas breakdown in the sub-nanosecond regime with voltages below 15 kV
  Krompholz, H.; Hatfield, L.L.; Kristiansen, M.; Hemmert, D.; Short, B.; Mankowski, J.; Brown, M.; Altgilbers, L.; Digest of Technical Papers, Pulsed Power Plasma Science, 2001. PPPS-2001. Volume 1, 17-22 June 2001 Page(s):487 - 490 vol.1
Abstract:  Gaseous breakdown in the sub-nanosecond regime is of interest for fast pulsed power switching, short pulse electromagnetics and for plasma limiters to protect devices from high power microwave radiation. Previous investigations of sub-nanosecond breakdown were mainly limited to high-pressure gases or liquids, with applied voltages in excess of 100 kV. In this paper, the authors investigate possibilities to achieve sub-nanosecond breakdown at applied voltages below 7.5 kV in point-plane geometries. The setup consists of a pulser (risetime between 400 ps to 1 ns), 50-/spl Omega/ transmission line, axial needle-plane gap with outer coaxial conductor, and a 50-/spl Omega/ load line. The needle consists of tungsten and has a radius of curvature below 0.5 /spl mu/m. The constant system impedance of 50 /spl Omega/ (except in the vicinity of the gap) and a special transmission-line-type current sensors enables current and voltage measurements with a dynamic range covering several orders of magnitude, with temporal resolution down to 80 ps. For pulse amplitudes of 1.7 kV (which are doubled at the open gap before breakdown) delay times between start of the pulse and start of a measurable current flow (amplitude > several milliamperes) have a minimum of about 8 ns, at a pressure of 50 torr in argon. Voltages of 7.5 kV produce breakdowns with a delay of about 1 ns. With negative pulses applied to the tip, at an amplitude of 7.5 kV, breakdown is always observed during the rising part of the pulse, with breakdown delay times below 800 ps, at pressures between 1 and 100 torr. At lower pressure, a longer delay time (8 ns at 50 mtorr) is observed. They authors expect the breakdown mechanism to be dominated by electron field emission, but still influenced by gaseous amplification.

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Publication Year:  1999
+ Energy efficiency analysis of an inductive storage system
  Kim, J.; Zhang, J.; Giesselmann, M.; Dickens, J.; Mankowski, J.; Kristiansen, M.; Digest of Technical Papers. 12th IEEE International Pulsed Power Conference, 1999. Volume 2, 27-30 June 1999 Page(s):1445 - 1448 vol.2
Abstract:  In this paper, the simulation and evaluation of energy efficiency and voltage amplification in an inductive energy storage system with resistive, capacitive and diode loads is presented. A numerical simulation with Mathcad shows that by proper reduction of the storage energy inductance and of the exploding fuse interruption time, the energy efficiency and voltage amplification can be greatly improved

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+ Energy Efficiency Analysis of an Inductive Storage System
  J. Kim, J. Zhang, M. Giesselmann, J. Dickens, J. Mankowski, M. Kristiansen, “Energy Efficiency Analysis of an Inductive Storage System”, Proceedings of the 12th IEEE International Pulsed Power Conference, Monterey, California, June 27-30, 1999.
Abstract:  Not Available
+ High voltage subnanosecond corona inception
  Mankowski, J.; Dickens, J.; Kristiansen, M.; Lehr, J.; Prather, W.; Gaudet, J.; Digest of Technical Papers. 12th IEEE International Pulsed Power Conference, 1999. Volume 2, 27-30 June 1999 Page(s):1392 - 1395 vol.2
Abstract:  Corona discharges in ultra-wideband radiating systems can have adverse effects on performance such as reflection, phase dispersion, and significant power losses. A test-bed has been assembled to experimentally observe corona created by voltage pulses similar to ultra-wideband systems. The current work involves the voltage attenuation of an incident pulse after propagation through a self-initiated corona and relative measurements of visible light emission from the photoionization produced during streamer development. Several gas dielectrics, including ambient air, N2, H2 , and SF6, were tested

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+ The design of a compact pulse transformer
  Zhang, J.; Dickens, J.; Giesselmann, M.; Kim, J.; Kristiansen, E.; Mankowski, J.; Garcia, D.; Kristiansen, M.; Digest of Technical Papers. 12th IEEE International Pulsed Power Conference, 1999. Volume 2, 27-30 June 1999 Page(s):704 - 707 vol.2
Abstract:  To improve the pulse shape and to obtain µs order pulse duration on a diode load in an inductive energy storage system, an oil-submerged compact pulse transformer with diameter of 20 cm and length of 70 cm has been designed and tested. From theoretical calculations, the parameters with primary inductance Lp=3.4 µH, secondary inductance Ls=90 µH, and coupling coefficient K=0.772 are obtained. To prevent breakdown, a conical secondary design is adopted. Under the condition of 500 kV operation voltage, the maximum electric field in the transformer is 205 kV/cm (in oil). The axial voltage distribution on the secondary is linear. Experiments have been done to test the insulation, the mechanical force and the coupling coefficient. The test results are consistent with the design parameters

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+ The Design of a compact Pulse Transformer
  J. Zhang, J. Dickens, M. Giesselmann, J. Kim, E. Kristiansen, J. Mankowski, D. Garcia, M. Kristiansen, “The Design of a compact Pulse Transformer”, Proceedings of the 12th IEEE International Pulsed Power Conference, Monterey, California, June 27-30, 1999.
Abstract:  Not Available
Publication Year:  1998
+ High voltage subnanosecond dielectric breakdown
  Mankowski, J.; Dickens, J.; Kristiansen, M.; IEEE Conference Record - Abstracts. 1998 IEEE International on Plasma Science, 1998. 25th Anniversary. 1-4 June 1998 Page(s):270
Abstract:  Summary form only given, as follows. Present day ultra-wideband (UWB) radiation sources a produce Megavolt pulses at 100's of picosecond (ps) risetimes. Empirical data on the breakdown characteristics for dielectric media at these short time lengths and high voltages are either extremely limited or non-existent. In support of the design of these UWB sources, we are investigating the breakdown characteristics, at these voltages and time lengths, of several liquids and gases. These include air, N2, H2, He, SF6, and transformer oil. The two voltage sources used in the experiments are capable of delivering 400 and 700 kV with a 400 ps risetime into an open load. These pulses are applied to the test gap area, capable of housing various gases and liquids at pressures from less than 1 to 150 atm. An empirical relationship of E-field versus breakdown time for the observed dielectrics is presented. Several other breakdown phenomena at these fast risetimes are observed. Dielectric breakdown strength dependence on polarity is investigated. Streak camera images of arc formation are captured, providing information on gap closure velocity. Also observed is the effect of ultraviolet radiation on the statistical lag time of breakdown for gas dielectrics at various pressures

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Publication Year:  1997
+ A subnanosecond high voltage pulser for the investigation of dielectric breakdown
  Mankowski, J.; Dickens, J.; Kristiansen, M.; Pulsed Power Conference, 1997. 1997 11th IEEE International Digest of Technical Papers. Volume 1, 29 June-2 July 1997 Page(s):549 - 554 vol.1
Abstract:  A high voltage, sub-nanosecond pulser is designed and built for the purposes of investigating dielectric breakdown. The requirement for the pulser is a voltage pulse of several hundred kilovolts, pulsewidth less than a few nanoseconds, and a risetime <400 psec. This is achieved by using pulse sharpening techniques on the output of a 500 kV Marx bank. Originally designed to stimulate a lightning strike, the voltage waveform from the Marx generator has a slow decay time of tens of µsec. In order to obtain a more desirable pulse, the Marx bank is modified. By removing a lumped-element resistor a higher peak output voltage with a faster risetime can be obtained. Circuit simulations have shown the capability of achieving an 800 kV output in less than 40 nsec to a charging (pulse forming) line. The 50 O impedance, oil-filled, pulse forming line consists of a peaking gap and pulse slicing gap. The peaking gap decreases the risetime of the applied pulse down to about 300 psec. The pulse slicing gap is included to short the voltage applied to the delay line and test chamber

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+ High voltage subnanosecond dielectric breakdow - 1997
  Mankowski, J.; Hatfield, L.; Kristiansen, M.; Agee, F.J.; Lehr, J.M.; Wells, J.; IEEE Conference Record - Abstracts., 1997 IEEE International Conference on Plasma Science, 1997. 19-22 May 1997 Page(s):317 - 318
Abstract:  Summary form only given. Present day ultra wideband radiation sources produce megavolt pulses at 100's of picosecond pulsewidths. Empirical data on the breakdown characteristics for dielectric media at these short time lengths and high voltages are either extremely limited or non-existent. In support of the design of these ultra wideband sources, we are investigating the breakdown characteristics, at these voltages and time lengths, of several liquids and gases. These include air, N2, H2, He, SF6, transformer oil, and freon-12

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