Browsing by Author "Mankowski, John J."
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Item A MULTI-STAGE DISTRIBUTED ENERGY PLASMA ARC RAILGUN(2010-12) Karhi, Ryan W.; Mankowski, John J.; Giesselmann, Michael G.; Bayne, Stephen B.; Rasty, Jahan; McNab, Ian; Wetz, David A.The development process pertaining to the design, fabrication, coding, and testing of multi-stage distributed energy plasma arc railguns are presented. In collaboration on an Air Force Office of Scientific Research (AFOSR) funded Multidisciplinary University Research Initiative (MURI) project, the Center for Pulsed Power and Power Electronics (P3E) at Texas Tech University is responsible for developing and investigating a functional scale model of a multi-stage distributed energy store (DES) railgun to analyze its effectiveness to suppress a restrike phenomenon and increase plasma armature railgun performance [1]. The term “restrike” denotes the formation of an electrical breakdown in the railgun bore some distance behind a traveling plasma armature. The formation of this secondary arc reduces the driving force on the primary armature and has led to a velocity ceiling of approximately 6 km/s on all breech-fed plasma armature railguns. Numerous solutions have been theorized as viable methods of restrike prevention but lack experimental verification. The primary objective of our research team within the MURI effort is to experimentally test Dr. Jerry Parker’s theoretical restrike suppression technique [2] that was developed at Los Alamos National Laboratory in the 1980’s. The project tasks are organized to identify potential problematic issues and verify theoretical concepts before implementation of a full scale system.Item A multistage distributed energy bench-top electromagnetic launcher(Texas Tech University, 2006-12) McDaniel, Bryan; Mankowski, John J.; Giesselmann, Michael G.A multi-stage energy distributed bench-top electromagnetic launcher is a way of testing the re-striking issues, which affect the velocity of the armature, associated with an electromagnetic launcher. Additional advantages of the multi-stage energy distributed scheme include a reduction in resistive losses and less residual inductive energy stored in the rails. An electromagnetic launcher is also known as a railgun. The bench top railgun used in a two stage energy distributed system sets the parameters and design for a five stage energy distributed system. The tests done on the five stage energy distributed system demonstrated real time switching of downstream stages. In addition to instrumentation control, diagnostics were built including Rogowski coils, B-dots, and a flux ruler. After the solid armature tests were completed, construction was started on a free running arc experiment. The results from this experiment will set up the parameters and design for a multi-stage energy distributed free running arc railgun.Item Compact, repetitive Marx generator and HPM generation with the Vircator(Texas Tech University, 2005-12) Chen, Yeong-Jer; Neuber, Andreas A.; Mankowski, John J.The electrical characteristics and design features of a low inductance, compact, 500 kV, 500 J, 10 Hz repetition rate, Marx generator for driving a high power microwave (HPM) source are described. This includes a relevant background discussion of Marx generators and HPM sources, with an emphasis on HPM generation with the virtual cathode oscillator (Vircator). The particular Compact Marx Generator design benefits 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 Ohm 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 stainless steel tube with 30 cm diameter and a total length of 0.7 m. 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 is discussed. A lumped circuit description of the Marx is also given, closely matching the experimental results. Preliminary design and testing of a low cost, all metal Vircator cathode are also discussed.Item Data acquisition and controls for hall effect thrusters(Texas Tech University, 1995-05) Mankowski, John J.Not availableItem Electrical, optical and x-ray diagnostics of subnanosecond breakdown in gases(2005-12) Kohl, Kevin Patrick; Krompholz, Hermann G.; Mankowski, John J.; Hatfield, Lynn L.Subnanosecond gas breakdown research is important for application in ultra-wideband radar (UWB), plasma limiters, and high speed switches for use in pulsed power applications. This paper contains breakdown data taken for voltage pulses having amplitude 150 kV and risetimes on the order of 250 ps. Voltage, current, and breakdown time constants are described in this paper for volume breakdowns and surface flashovers. In addition, the x-ray emission and the luminosity were measured. All results point to the importance of runaway electrons for this discharge regime.Item Electrical, optical and x-ray diagnostics of subnanosecond breakdown in gases(Texas Tech University, 2005-12) Kohl, Kevin Patrick; Krompholz, Hermann G.; Mankowski, John J.; Hatfield, Lynn L.Subnanosecond gas breakdown research is important for application in ultra-wideband radar (UWB), plasma limiters, and high speed switches for use in pulsed power applications. This paper contains breakdown data taken for voltage pulses having amplitude 150 kV and risetimes on the order of 250 ps. Voltage, current, and breakdown time constants are described in this paper for volume breakdowns and surface flashovers. In addition, the x-ray emission and the luminosity were measured. All results point to the importance of runaway electrons for this discharge regime.Item Electro-explosive fuse optimization for FCG current sources(2007-12) McCauley, David R.; Mankowski, John J.; Neuber, Andreas A.As high power microwave (HPM) systems become more prevalent in defense technology, the need arises to make compact systems capable of delivering energy with the same order of magnitude as a large scale system. Various Pulsed power systems have been designed with compact flux compression generators (FCGs) which have very large energy densities to provide the initial current amplification. HPM systems require large voltages, not large currents; therefore a power conditioning system capable of transforming large currents from the FCG to large voltages, to drive the HPM source, is required. This can be done with an FCG driving an inductive energy storage system (IESS) with an electro-explosive fuse (EEF) in the current path. The interruption of current by the fuse will cause a large voltage spike that is in the right regime for high power microwaves. Often the electro-explosive fuse can be the largest component in the system; therefore, the need for optimization arises to reduce the size of the fuse without affecting the voltage multiplication of the fuse. This thesis will examine various parameters that control the operation of the fuse to find the maximum voltage multiplication possible while reducing the overall fuse size. Optimization of the individual parameters of the fuse including quenching media, fuse material, fuse strand length, and fuse shape will lead to complete optimization of the fuse. The end result will be a compact optimized electro-explosive fuse to be implemented in an FCG driven high power microwave system.Item Evaluation of a high-pressure, coaxial spark gap for pulsed ring-down applications(2007-12) James, Colt; Dickens, James C.; Mankowski, John J.The design and jitter performance of a high pressure, coaxial spark gap for use in pulse ring-down applications is presented. Additional comparisons with trigatron style triggering are also presented. The spark gap is triggered by field distortion of a center plane electrode. The switch was tested up to 75 pulses per second (pps) with a maximum switching voltage of 50 kV in nitrogen. Analysis will focus on jitter measurements taken over the full lifetime of the switch. This paper presents the results of this analysis along with comparisons from the literature. Specifically, switch jitter and lifetime will be evaluated as a function of switch geometry as a whole and as a function of trigger electrode geometry.Item Experimentation and modeling of pulse sharpening and gyromagnetic precession within a nonlinear transmission line(2011-08) Vaselaar, Andrew; Bayne, Stephen B.; Mankowski, John J.A computer model is developed to predict the output of a NonLinear Transmission Line (NLTL) based upon an input pulse, material properties and physical dimensions. Additionally, a test bed is developed with the goal of validating the computer model with regards to its level of accuracy in comparison with a real world system. The test bed is also designed to provide the apparatus for evaluating ferrite materials for their performance characteristics as components for NLTL applications. The resulting model provides two computation algorithms that successfully simulate aspects of NLTL operation. They require further development to improve their computational algorithms and to take into account more material properties in order to serve as a better tool for design of NLTL systems. The NLTL testbed results in a working pulser and diagnostic system, however the NLTL suffers from high voltage breakdown that prevents it from functioning as designed.Item High voltage subnanosecond dielectric breakdown(Texas Tech University, 1997-12) Mankowski, John J.Current interests in ultrawideband radar sources are in the microwave regime, which corresponds to voltage pulse risetimes less than a nanosecond. Some new sources, including the Phillips Laboratory Hindenberg series of hydrogen gas switched pulsers, use hydrogen at hundreds of atmospheres of pressure in the switch. Unfortunately, the published data of electrical breakdown of gas and liquid media at times less than a nanosecond are relatively scarce. A study was conducted on the electrical breakdown properties of liquid and gas dielectrics at subnanosecond and nanoseconds. Two separate voltage sources with pulse risetimes less than 400 ps were developed. Diagnostic probes were designed and tested for their capability of detecting high voltage pulses at these fast risetimes. A thorough investigation into E-field strengths of liquid and gas dielectrics at breakdown times ranging from 0.4 to 5 ns was performed. The breakdown strength dependence on voltage polarity was observed. Streak camera images of streamer formation were taken. The effect of ultraviolet radiation, incident upon the gap, on statistical lag time was determined.Item Intrumentation and control of electromagnetic launchers(2007-08) Karhi, Ryan W.; Mankowski, John J.; Dickens, James C.; Hemmert, David J.The instrumentation and control of electromagnetic launch technology is presented. All of the experimental work and theory presented refer to one specific type of launcher know as a railgun. Two railgun projects supported by the AFOSR are described. One is an STTR phase 1 contract to develop a fast transient control system for solid state switching of numerous capacitor banks for implementation on a railgun. The other is a MURI project in collaboration with the IAT at the University of Texas for low cost access to launch micro-satellites into orbit. A project goal for both funded projects was to design and test control systems for the application of multi-stage railgun timing control. This relatively new area of railgun research is attributed to the need for complex multi-stage systems. The paper starts with control systems for proof of principle solid armature experiments and ends with a controlled asynchronous free-running arc distributed energy system.Item Performance of a mobile solid state GPS linked pulsed ring down array(2011-08) Reale, David V.; Mankowski, John J.; Bayne, Stephen B.The development of mobile Pulsed Ring Down Source (PRDS) arrays requires the ability to accurately determine the relative positions of array elements at distances, and in situations, where discrete measurements are not practical. At the frequencies of interest, centimeter level accuracy is required for the array to localize radiated energy at a given target location. Global Positioning System (GPS) devices and techniques are evaluated for the purpose of position acquisition. A Monte Carlo simulation was developed that takes into account the position error, the GPS timing error, and the switch jitter of the element. The error sources are combined and used a metric to evaluate and predict the array performance. Results of the GPS device testing, as well as previous work, are used as the input parameters of the simulation to determine their viability for use in the implementation of PRDS arrays. An array of low power solid state pulsed ring down sources are used to verify the results of the Monte Carlo simulations.Item Pulsed ring-down antennas for implementation in a phased array(Texas Tech University, 2008-08) Belt, David W.; Mankowski, John J.; Dickens, James C.; Kristiansen, MagneIn recent years, the development of directed energy systems has greatly increased, but a majority of the systems still lack the desired compactness for field application. The pulsed ring-down antenna has become of great interest due to its compact size and peak power on target potential. A pulsed ring-down antenna operates by charging the single element antenna with a high potential source and then closing a switch to develop transient wave reflections on the antenna. Typical CW case analysis does not apply in this case. Since these systems are fairly new in study, it is often difficult to predict the overall performance without experimental evaluation. For this reason, we have constructed a simulation model that allows us to predict the transient behavior of the structure. By utilizing the Comsol RF module transient analysis functions, we are able to characterize various parameters of different antennas, beginning with a dipole pulsed ring-down antenna operating around the 100 MHz range. After examining the simulated results against the experimental results for accuracy, we then moved to more complicated Mesoband antenna structures. The simulation model developed within the COMSOL RF module allows us to examine various influential factors such as material losses, transient switching effects, structure capacitance, switch capacitance, and initial charging losses. With this, we are able to examine methods to improve the results in the far field such as capacitive spark gap loading and other capacitive storage methods. Utilizing the pulsed ring-down antenna model, we are able to give a better characterization of mesoband pulsed ring-down structures for implementation into a specific or multi-purpose phased array system. Several of these structures were then constructed, tested, and characterized based upon far field performance. Once the optimal antenna was determined, a five element phased array was constructed. Initially, the phased array is designed to operate at two different phase angles via delay lines. Future systems may incorporate dynamic phase shifting by other means based upon these initial results. With the tools and initial measurements now available, the design of a pulsed ring-down phased array can easily be completed.Item The impact of field enhancements and charge injection on the pulsed breakdown strength of water(2006-05) Wetz, David A.; Mankowski, John J.; Kristiansen, Magne; Dickens, James C.In any high voltage pulsed power system there is a need for a dielectric material to serve as a charge storage medium, switching medium, or insulator. Water, with its high dielectric constant, εr = 81, and favorable physical properties is an ideal candidate for use in compact pulsed power systems. Several research efforts have been conducted over the last several decades to investigate possible ways of increasing water’s dielectric strength [Joshi, Kun]. In the research documented here, experiments have been conducted in order gain further insight into the mechanisms that initiate the electrical breakdown of water. With the application of a large enough pulsed electric field, any metal conductor will begin to emit electrons from its surface, especially from field enhancements on the electrode surface, into the dielectric region. This emission initiates the breakdown of water, though various theories of exactly what happens in the water prior to breakdown have been developed. Some suggest that the breakdown event is purely electronic where the emission enters the gap until a conductive channel is formed [1]. Others have suggested that the emission causes rapid heating within the water causing it to vaporize and a bubble to form [2,3,4]. Neither theory has been conclusively confirmed as the primary mechanism. Several factors have been found to either increase or decrease the electric holdoff strength of water including the electrode surface roughness, the electrode material, the electrode surface area, and the water conductivity. Experiments have been conducted to test the effect each of these factors has on water’s dielectric strength and in each experiment, a water gap was tested under pulsed conditions with pulse widths of roughly 2 μs. Peak electric fields over 1 MV/cm and peak currents over 3.5 kA have been recorded across the gap. In all of the tests, electrodes machined with a Bruce profile were used on both the anode and cathode sides of the gap. Random and known surface roughness patterns were applied to the electrodes through mechanical sanding and etching processes. Surface roughnesses ranging from 0.26 ìm to 1.96 ìm and electrode surface areas ranging from 0.44 cm2 to 75 cm2 were tested. Electrodes constructed of various materials including Aluminum, Molybdenum, Copper, Tungsten, Nickel, Stainless Steel, and Zinc Oxide, all of which had a constant surface area of 5 cm2, were also tested. The conductivity of the water was varied from 1 µS/cm to 38.5 µS/cm. Additionally, shadowgraph images of a point plane geometry were taken to further understand the breakdown processes that occur.Item The impact of field enhancements and charge injection on the pulsed breakdown strength of water(Texas Tech University, 2006-05) Wetz, David A.; Mankowski, John J.; Dickens, James C.; Kristiansen, MagneIn any high voltage pulsed power system there is a need for a dielectric material to serve as a charge storage medium, switching medium, or insulator. Water, with its high dielectric constant, εr = 81, and favorable physical properties is an ideal candidate for use in compact pulsed power systems. Several research efforts have been conducted over the last several decades to investigate possible ways of increasing water’s dielectric strength [Joshi, Kun]. In the research documented here, experiments have been conducted in order gain further insight into the mechanisms that initiate the electrical breakdown of water. With the application of a large enough pulsed electric field, any metal conductor will begin to emit electrons from its surface, especially from field enhancements on the electrode surface, into the dielectric region. This emission initiates the breakdown of water, though various theories of exactly what happens in the water prior to breakdown have been developed. Some suggest that the breakdown event is purely electronic where the emission enters the gap until a conductive channel is formed [1]. Others have suggested that the emission causes rapid heating within the water causing it to vaporize and a bubble to form [2,3,4]. Neither theory has been conclusively confirmed as the primary mechanism. Several factors have been found to either increase or decrease the electric holdoff strength of water including the electrode surface roughness, the electrode material, the electrode surface area, and the water conductivity. Experiments have been conducted to test the effect each of these factors has on water’s dielectric strength and in each experiment, a water gap was tested under pulsed conditions with pulse widths of roughly 2 μs. Peak electric fields over 1 MV/cm and peak currents over 3.5 kA have been recorded across the gap. In all of the tests, electrodes machined with a Bruce profile were used on both the anode and cathode sides of the gap. Random and known surface roughness patterns were applied to the electrodes through mechanical sanding and etching processes. Surface roughnesses ranging from 0.26 ìm to 1.96 ìm and electrode surface areas ranging from 0.44 cm2 to 75 cm2 were tested. Electrodes constructed of various materials including Aluminum, Molybdenum, Copper, Tungsten, Nickel, Stainless Steel, and Zinc Oxide, all of which had a constant surface area of 5 cm2, were also tested. The conductivity of the water was varied from 1 µS/cm to 38.5 µS/cm. Additionally, shadowgraph images of a point plane geometry were taken to further understand the breakdown processes that occur.