Showing papers on "Marx generator published in 2007"

Repetitive and High Voltage Marx Generator Using Solid-state Devices

Abstract: Repetitive high voltage pulsed power system proposed in this study originates from conventional Marx generators. This newly developed Marx modulator employs high voltage (HV) insulated gate bipolar transistors (IGBT) as switches and series- connected diodes as isolated components. Self-supplied IGBT drivers and optic signals are used in the system to avoid insulation problem. Experimental results of 20 stages generating pulses with 60 kV, 20-100 mus and 50~500 Hz are presented to validate the performance of the system in the paper.

Cathode and Anode Optimization in a Virtual Cathode Oscillator

Abstract: We are fabricating and testing several different types of cathodes for the same vircator driven by a single shot Marx generator and pulse forming line (300 kV, 60 ns, 30 Omega). The cathodes types, each with an emitting area of ~32 cm2, include the original velvet with a new geometry, carbon fiber, pin-array, and an array of all metal cathodes. The metal cathodes are made from aluminum and oxygen free copper fashioned to similar geometries with either a chemical etch or a CNC machining process. The vircator is tested with all of these cathodes using both polarity configurations and evaluated for beam voltage, current density, microwave output, and single shot lifetime. In addition to the cathode testing, several stainless steel and tungsten anode meshes with varying transparencies (50% - 80%) are evaluated. The construction and testing of an anode fashioned from Tantalum (70% transparency) is also discussed. Electron beam uniformity of the metal cathodes is investigated with the emitted electron beam current-density distribution evaluated in both time and space. Optimization of output power using resonant effects is also examined.

Gigawatt Emission From a 2.4-GHz Compact Magnetically Insulated Line Oscillator (MILO)

Abstract: High-power-microwave (HPM) emission has been observed in S-band with a compact magnetically insulated line oscillator (MILO). The device is driven by a low-impedance Marx generator which was designed and built at Commissariat a l'Energie Atomique, Centre d'Etudes Scientifiques et Techniques d'Aquitaine for HPM experiments. Measurements with fast and sensitive I-dot probes, installed inside the slow-wave structure (SWS), have given the evidence of the MILO oscillation. The main frequency at 2.40 GHz is confirmed by measuring the emitted radiation by using both an in-vacuum antenna and a horn placed in the far-field region. The frequency response of the MILO SWS is compared to a 3-D simulation performed with MAGIC, an electromagnetic particle-in-cell code. In the first configuration, a microwave output power of 1 GW has been obtained, which is in good agreement with the simulations. Then, an optimization of the cathode geometry has led to an increase of the pulse duration and to a better stability of the emission frequency. Finally, based on the fair agreement between the experimental results and the corresponding simulations, a novel design is presented, which should give a higher emitted power at 2.34 GHz.

Characterization and analysis of a pulse power system based on Marx generator and Blumlein

Abstract: A pulse power system (1MV, 50kA, and 100ns) based on Marx generator and Blumlein pulse forming line has been studied for characterization of a general system. Total erected Marx inductance and series resistance are calculated from modular testing of Marx generator and testing of Marx generator with Blumlein. The complete pulse power system has been tested with the termination of a liquid resistor load for finding the Blumlein characteristic impedance. Equivalent electrical circuits during the charging and discharging of the Blumlein are constructed from the characterized parameters of the system. These equivalent circuits can be used in the analysis of prepulse voltage and droop in the flat top of the main pulse in the pulse power systems based on Marx generator and Blumlein.

High Voltage Marx Generator Implementation using IGBT Stacks

Abstract: High voltage Marx generator implementation using IGBT (Insulated Gate Bipolar Transistor) stacks is proposed in this paper. To protect the Marx generator at the moment of breakdown, AOCP (Active Over-Current Protection) part is included. The Marx generator is composed of 12 stages and each stage is made of IGBT stacks, two diode stacks, and capacitors. IGBT stack is used as a single switch. Diode stacks and inductors are used to charge the high voltage capacitor at each stage without power loss. These are also used to isolate input and high voltage negative output in high voltage generation mode. The proposed Marx generator implementation uses IGBT stack with a simple driver and has modular design. This system structure gives compactness and easiness to implement the total system. Some experimental and simulated results are included to verify the system performances in this paper.

An Overview of Pulse Compression and Power Flow in the Upgraded Z Pulsed Power Driver

Abstract: Summary form only given. The Z pulsed power driver at Sandia National Laboratories is used to develop high energy density Z-pinch X-ray sources for inertial confinement fusion research and radiation effects testing, and drive megabar pressures in material samples for equation of state studies. The pulsed power system is in the process of being replaced, improving reliability and increasing energy delivered to the load. The upgraded pulsed power system will deliver more than nine megajoules of forward wave energy in the first one hundred nanoseconds of its pulse. The system is comprised of thirty-six nominally identical modules, each producing a 3.3-terawatt pulse in 6Omega water-insulated transmission lines. The peak forward-going voltage is about 5 MV. The pulse rise time is -75 ns; the full width at half maximum is -190 ns. The thirty-six modules are combined in parallel and drive twenty to twenty-five MA into the single load. In such a system, reliable insulation and precise switching are primary concerns. We show key components of the system and results from a test module. We also show performance results from the energy storage, triggering, and pulse-forming systems. We also show the differing constraints of power flow from the 175 kA from each Marx generator, to currents in excess of 24 MA in the final feed to the load.

Application of a fast electrical pulse in gated multichannel plate camera.

Abstract: An eight-frame gated microchannel plate (MCP) camera and a gating electrical pulse are described in this article. The gating electrical pulse is obtained by first generating a high voltage fast step pulse using avalanche transistors in Marx bank configuration, and then shaping it using avalanche diodes. The high voltage fast step pulse is about 200 ps in fall time and 4 kV in amplitude. The gating pulse wave form with width of 160 ps and amplitude of 2.5 kV is achieved. Each frame photocathode coated with gold on the MCP is part of a 12 Omega transmission line with open circuit end driven by the gating electrical pulse. The camera is tested by illuminating its photocathode with ultraviolet laser pulses, 266 nm in wavelength, which shows exposure time as short as 120 ps.

Active Charge/Discharge IGBT Modulator for Marx Generator and Plasma Applications

Abstract: In this paper, we present a Marx-stackable insulated-gate-bipolar-transistors-based modulator for plasma ion implantation and other pulsed high voltage-high peak power applications. Active control of charging and discharging cycles permits rigid pulse forms, arbitrary duty cycles and internal efficiencies exceeding 90%. We demonstrate a 20-kV 15-A generator using a 2-kV Marx generator to drive a pulse transformer

Solid-state Marx Generator Design with an Energy Recovery Reset Circuit for Output Transformer Association

Abstract: This paper presents a hybrid fully integrated solid- state Marx generator circuit, which has been developed for high-frequency (kHz), high-voltage (kV) applications needing rectangular pulses. The proposed circuit takes advantage of the intensive use of power semiconductor switches to increase the performance of the classical Marx circuit, strongly reducing losses and increasing the pulse repetition frequency. In addition, to further increase the output pulse, the proposed topology is enhanced with an energy recovery reset circuit that enables the use of an output pulse transformer, and recovers the transformer magnetizing energy, during the pulse off state, back to the energy storage capacitors.

Bipolar pulse generator for intense pulsed ion beam accelerator.

Abstract: A new type of pulsed ion beam accelerator named “bipolar pulse accelerator” (BPA) has been proposed in order to improve the purity of intense pulsed ion beams. To confirm the principle of the BPA, we developed a bipolar pulse generator for the bipolar pulse experiment, which consists of a Marx generator and a pulse forming line (PFL) with a rail gap switch on its end. In this article, we report the first experimental result of the bipolar pulse and evaluate the electrical characteristics of the bipolar pulse generator. When the bipolar pulse generator was operated at 70% of the full charge condition of the PFL, the bipolar pulse with the first (−138kV, 72ns) and the second pulse (+130kV, 70ns) was successfully obtained. The evaluation of the electrical characteristics indicates that the developed generator can produce the bipolar pulse with fast rise time and sharp reversing time.

An all solid-state pulsed power generator based on Marx generator

Abstract: High voltage pulsed power supply with high repetitive rate has found wide applications in industry, and military such as plasma source for ion implantation, microwave generator and high pulsed power laser. The conventional pulsed power supply is limited by gas switch with short lifetime and low repetitive frequency. In recent years Marx generator based on solid state switches has proposed. It has dual functions by combining high repetitive rate from semiconductor switch with voltage adder from Marx generator principle. The solid state switches can be MOSFET , IGBT or SCR. This all-solid-state pulsed power supply has multifold advantages such as flexibility of pulse voltage amplitude, pulse width and repetitive rate and long lifetime and compactness.

Green-laser-triggered Water Switching at 1.6 MV

Abstract: Multiple water switches are used in the self-breaking mode in many large pulsed power systems. We are studying laser-triggering of water switches at voltages of up to 1.6 MV to see whether we can lower the command jitter of water switches. We have previously reported studies of 170 kV water switching with command jitters as low as plusmn2 ns. The 1.6 MV triggering experiments reported here are performed on a water switch in the middle of a 1.8 m long 7.8 Omega coaxial water line that is directly charged by a 65 kJ Marx generator. The 10 to 90% rise-time of the sinusoidal pulse impressed across the water switch is 250 ns. To trigger the switch, we transport a green laser beam (0.4 J, 7 ns pulsewidth) radially inward though the water of the coaxial line to a 'dry box' inside the inner coax line. There, the laser beam is turned 90 degrees and focused through a hole in one electrode to a breakdown arc in the water between the switch electrodes. Best results, of plusmn8.3 ns jitter and 100 ns delay at 60% of the self-break voltage, have been achieved using an axicon lens to focus the beam to a long narrow chain of point breakdowns between the switch electrodes.

Impedance matching of a coaxial Marx generator with a relativistic field emission limited diode

Abstract: The impedance matching between the coaxial Marx generator and the relativistic field emission limited diode (RFELD) is investigated by using PSpice simulations. The PSpice model of the coaxial Marx generator has been built and verified by comparing the output voltage wave forms with the results of Kubota et al. [Y. Kubota, J. Kodaira, and A. Miyahara, Jpn. J. Appl. Phys. 20, 2397 (1981)]. By varying the passive resistive loads, the impedance of the coaxial Marx generator can be determined. In the PSpice simulation, we employ the analog behavioral modeling to describe the current-voltage characteristics of the RFELDs. The output characteristics including the voltage, current, and output power wave forms have been obtained. It is found that the output characteristics of the RFELDs with an effective work function of around 0.4 eV are in good matching with the coaxial Marx generator. The simulation results show a degradation in pulse duration or beam power for the cases of the RFELDs with higher or lower effe...

Method and device for production and emission of a high-power microwave pulse

Abstract: The production and emission of high-energy microwave pulses are made possible by means of a device with a particularly compact design if the capacitor column ( 12 - 12 ) of the Marx generator ( 11 ) whose series circuit conventionally itself feeds a microwave generator with a matched antenna geometry, is now itself used—dispensing with the microwave generator and its antenna—directly as a resonator and Hertzian antenna dipole ( 24 ). Its oscillation response can be optimized by triggered spark gaps ( 14 ) for the switching of capacitors ( 12 ), and by means of plates ( 19 ) connected at the ends, in order to increase the stray capacitances.

A Bipolar Marx Generator for a Mobile Electroporation Device

Abstract: Summary form only given. For the industrial electroporation of plant cells it is of advantage to set up the electroporation reactor in a bipolar configuration. With the electrodes pulsed simultaneously with the same voltage of opposite polarity, in order to achieve the same electric field strength, less effort for the insulation to ground is necessary than for an unipolar reactor. The required voltage can be delivered by a bipolar Marx generator. For a reliable operation of such a configuration, the way the generator and the load are grounded is essential. To prevent the power supply from an over-voltage in the case of an undesired Hash-over inside the electroporation reactor, a good ground connection at the center of the generator keeps the potential at the supply clamps low. But this measure has an influence on the coupling of the two sides of the generator during the switching process and might require an additional capacitive coupling path. A transient insulation to ground by means of a coil fosters a better switching behavior, but in the case of a flash-over the generator potential may float resulting in an over-voltage. Here, an additional over-voltage protection for the power-supply is required. In the work the different approaches for the ground connection are discussed.

Development and testing of the ilc marx modulator

Abstract: Construction of the SLAC/ILC 'Reference Design' Marx Modulator is complete and testing is currently underway at SLAC. This modulator design is oil-free, air-cooled, and capable of delivering 120 kV, 140 A, 1400 musec pulses at a rate of 5 Hz. Total energy per pulse is 23,500 joules. Projected efficiency is greater than 96%. The Marx modulator design employs a stack of sixteen 12 kV Marx modules that generate high-voltage output pulses directly from a 12 kV input supply voltage. This direct switching eliminates the requirement for a massive transformer and reduces the capacitor bank size by more than a factor of four, yielding a considerably cheaper and more compact mechanical solution. Advantages of the ILC Marx design include higher efficiency, smaller physical size, and a modular architecture that provides greater reliability and cost- effective PC board-level integration.

Compact Marx Generator for Repetitive Applications

Abstract: Summary form only given. We designed a compact repetitive Marx generator. The Marx generator contains 25 stages consisted with capactor banks and spark gap switches. We used door knob ceramic capacitors. The capacitors are charged through inductors by a capacitor charging power supply. The length and the diameter of the Marx generator are about 150 cm and 60 cm, respectively. We conducted a preliminary test at the condiction of low charging voltage using helium gas. We present the characteristic of the Marx generator and discuss the design issues such as the insulation of a high voltage feedthrough.

Characterization of Runtime and Jitter on a Laser Triggered Spark Gap Switch

Abstract: Summary form only given. A 1 MV, SF6 filled, laser triggered gas switch has been installed on the University of Missouri pulsed power test stand to study the factors affecting runtime and jitter. The test stand consists of a 2.8 MV, 450 kJ Marx bank that feeds into a 7 nF intermediate store capacitor before discharging through the gas switch. The test was operated from about 1 MV up to 2.5 MV, at switch pressures from 1 to 4 atm. The gas switch is triggered by a 30 mJ New Wave Tempest 10 Nd:YAG laser to initiate breakdown in the switch. The University of Missouri has examined factors including the applied field, rate of rise and gas pressure of the switch along with the laser power, focused intensity, and Rayleigh range and determined their relation to jitter and runtime. Optical spectroscopy has been used to examine both the laser arc and the resulting switch discharge plasma parameters and composition. The end goal of research is to understand the factors contributing to increased jitter and runtime and thereby provide paths to improved switch performance.

Marx Bank Technology for the International linear collider

Abstract: Diversified Technologies, Inc. (DTI) has developed a high power, solid-state Marx bank topology for the ILC modulators and power supplies that can deliver equivalent performance and yield acquisition cost savings of 25-50% versus presently proposed alternatives. In this paper DTI will describe the Marx based technology as it is applied to ILC power systems design, and review recent progress in the engineering of the prototype transmitter being built under a Phase II SBIR from the DOE.

Dual-Waveform Ringing Gain Analysis and its Application to Pre-Pulse Reduction on Blumlein-Based X-ray Machines

Abstract: Summary form only given. Pulsed-power machines at AWE are routinely used for flash X-ray radiographic applications in the 1-10 MV range to drive high-and low-impedance e-beam diodes. During the pulse-forming line (PFL) charging phase, certain diode types are sensitive to pre-pulse voltages as low as a few tens of kilovolts due to small anode-cathode gaps and geometries that enhance electric fields. This results in electron emission before the main pulse is applied which can prevent the diode from operating properly. It is therefore crucial to limit the pre-pulse voltage appearing at the diode to below the emission level. A Blumlein PFL, as used on all AWE machines at present, comprises three co-axial cylindrical conductors, the outer one of which is grounded. The intermediate conductor, of voltage Vin, is charged from the output of a Marx bank. An output pulse is created on the inner conductor on closure of an oil-switch which shorts the inner and intermediate Blumlein conductors. Prior to closure of this switch, the voltage of the inner Blumlein conductor, denoted by Vi, which is actually the pre-pulse voltage, must be kept as close to ground as possible. This can be accomplished using a balance circuit, comprising two inductors (Li & Lo) and two damping resistors (Ri & Ro) which connect to the base of the Marx bank. For ideal electrical balance, the ratios Li:Lo and Ri:Ro must equal the ratio Co:Ci where Co is the capacitance between the outer and intermediate Blumlein conductors and Ci is the capacitance between the inner and intermediate Blumlein conductors. Practical circuits will likely have some level of imbalance and non-zero pre-pulse voltage (Vi). This situation cannot be dealt with by the standard AWE ringing gain analysis method which applies solely to the charging waveform (Vin) and gives values only for such parameters as: Marx parallel resistance (Rp), series resistance (Rs) and inductance (Ls), based on the match between analytical and machine waveforms. By extending the analysis to the pre-pulse voltage (Vi), values of the balance circuit components (Li, Lo, Ri & Ro) can also be obtained. The Laplace transform technique is used, taking into account non-zero initial conditions, and the solution in the time domain obtained by applying Heaviside's expansion theorem. Theory predicts that, when there is electrical imbalance, an oscillatory perturbation to the charging waveform (Vin) will result and give rise to pre-pulse voltage (Vi) which can be high. These findings are consistent with experimental observations. On Blumlein-based machines, dual-waveform ringing gain analysis should assist in: (i) keeping the electrical system balanced, (ii) reducing pre-pulse voltage levels, and (iii) allowing ringing gain analysis to be performed on machines with serious electrical imbalance.

Electroporation of agricultural produce, especially sugar beet, to improve juice yield, is carried out using intensive high tension impulses produced with multi-stage Marx generator

Abstract: Electroporation of agricultural produce, using intensive high tension impulses (HTI's) is carried out with a multi-stage Marx generator (MG) The HTI's are generated and coupled in the first stage of the MG; and are obtained by discharging a capacitorusing a closed semiconductor circuit The amplitude of the HTI's is increased to the transport potential by an impulse transformer Electroporation of agricultural produce, using intensive high tension impulses (HTI's) is carried out with a multi-stage Marx generator (MG), triggered with HTI's to a suitable time point The HTI's are generated and coupled in the first stage of the MG and lead to overvoltage longitudinal triggering of the first spark zone of the MG The HTI's are obtained by discharging a capacitor (capacitative energy store) using a closed semiconductor circuit, and the amplitude of the obtained HTI's is increased to the transport potential by an impulse transformer An independent claim is included for a circuit arrangment for carrying out the process, with the MG (having a predetermined number of individual stages) and a triggering device for the MG A device (100) for generating and coupling HTI's in the MG causes overvoltage longitudinal triggering of the first spark zone of the MG The The HTI results from discharge of capacitative energy store in the primary side of a high tension transformer (110) with a closed semiconductor circuit

Isolated Autonomous Capacitive Power Supplies to Trigger Floating Semiconductors in a Marx Generator

Abstract: This paper reports the development of isolated autonomous capacitive power supplies to charge each drive circuit of the high voltage floating semiconductor stage in a solid-state Marx generator. The circuit takes advantage of an auxiliary capacitor, charged in series with the main energy storage capacitor in each Marx generator stage, to supply the optic-fibre isolated gate drive circuit of the solid state switches. Laplace domain circuit analysis is made to determine the values of these capacitors and to obtain the desired voltages, with low ripple, for the required load. A laboratory prototype with three stages, 3 kW peak power, of this all silicon Marx generator circuit, with optic- fibre isolated triggering signals and autonomous capacitor isolated charging power supplies was built using 1200 V IGBTs and diodes, operating with 1000 V d-c input voltage and 10 kHz frequency, giving 3 kV and 10 mus pulse with, approximately, 15 V isolated autonomous power supplies in each stage.

Design and Performance of Capacitive Divider for High-voltage Pulse Measurement

Abstract: Several capacitive dividers and V-dot monitors were designed to measure high-voltage pulseThe monitors were installed on water transmission line and pulse forming lineThe capacitor from cathode to the probe was the high-voltage arm of divider,which could reduce the structural inductance when the low-voltage arm of the capacitive divider was a ceramic capacitor ring and the structure was designed as coaxialThe V-dot monitor was another capacitive divider without the low-voltage armThe output of V-dot was proportional to the time derivative of the voltageAnd the signal proportional to voltage was given by a RC integratorIt could impair electric field intensity in water-plastic-metal triple-point when the surface of probe's insulation was lower than the probeThe position of probe compared to the inner-surface of anode could be immovable when pressurized ring was put in the grooveIt could hold the sensitive of monitor changeless even if the probe was installed againThe monitor was calibrated in site with a calibrated resistive dividerThe resistive divider was fixed to another side of coaxial line to reduce the change of electric field about the monitorAll monitors worked well at the highest Marx bank charge voltagesThe capacitive divider and the V-dot monitor could response the signal of which raise time was from several decade nanoseconds to near microseconds when designed value and the distributed parameter of structure were proper

A Novel Multi-Level High Voltage Pulsed Power Generator

Abstract: This paper presents a novel solid-state and high power pulse generation technique that is suitable for a wide range of pulsed power applications The technique, termed as multi-level pulsed power converter, can be considered as a hybrid of the direct discharge type and the Marx generator but with considerably less complexity in both control and circuitry It has the ability for generating pulses with flexible amplitude and duration similar to that of a Marx generator, and unlike the direct discharge type requires no voltage balancing and snubbing circuitry As voltage balancing is inherent to the technique, the timing between switching events is not critical to balance the voltage stresses and as such the driving circuitry of the converter is relatively simple The validity of the proposed technique is verified by presenting both theoretical analysis and simulation results of a 3-stage, 3 kV converter

Repetitive All Solid State Pulse Marx Type Generator with Energy Recovery Clamp Circuit for Indutive Loads

Abstract: Summary form only given. In the last decade, repetitive high-voltage pulses have been used extensively in industrial applications, as for example in food sterilization and surface engineering, which increased the need of efficient, flexible and suitable power supplies, based on solid state switches. A number of techniques have been used in order to generate high-voltage pulses from generators with optimised performance and characteristics, taking the best of solid-state technology. One of these is the mature Marx generator concept that as has been intensively used through the years, with significant technological improvements to increase the performance of the original circuit. We will report on a newly developed Marx type circuit to achieve both output-voltage multiplication and energy recovery that has been developed for inductive load applications, namely electromagnetic forming, based on an all-solid state Marx type generator. The proposed circuit takes advantage of the power semiconductor hard switches intensive use, replacing the conventional Marx bank passive elements, to increase the performance, strongly reducing losses and increasing the pulse repetition frequency. Additionally, the generator is designed with an energy reset circuit that enables the use of inductive loads, recovering the inductive energy during the hard switches off state, back to the energy storage capacitors. This decreases the charging time, and enables higher frequency operation, increasing the pulse generator yield. The high voltage measurements of the generator output will be presented and compared with the results of circuit simulations.

Surface Flashover of Dielectric Materials Used in Pulsed Power Research

Abstract: Summary form only given. Insulator technology has evolved steadily for power transmission and distribution applications over the past 30 years, allowing for reliable design rules and testing procedures to be developed. These rules and procedures have been validated for applications under DC. and power frequency conditions (50/60 Hz and 400 Hz in aircraft applications), allowing for the appropriate choice of insulation to be made. Selection procedures for insulators to be used under high voltage/high-current pulsed power conditions are however, not well defined, and insulator failure has occurred in large pulsed power facilities when the materials were selected based on experience with low frequency systems. This work is being undertaken to investigate dielectric material behavior under high dE/dt conditions. A 10-stage Marx generator, capable of producing output voltages in the region of 750 kV, is used in conjunction with an adaptable test assembly to determine the flashover properties of different materials. Results on the dielectric behavior and ageing of solid insulators are reported, along with hold-off voltage performance and degradation due to surface discharges.

Reversible, high-voltage square-wave pulse generator for triggering spark gaps

Abstract: A design is presented for a reversible, square-pulse generator that employs coaxial cables for charge storage and pulse formation and a thyratron as the switch. The generator has a nominal output voltage of 5-30 kV and a pulse duration determined by the cable's physical length. Two variations are presented: (1) a single-stage one consisting of cable that is charged via its shield on one end and discharged with a thyratron on the opposite end and (2) a two-stage one having an inverting circuit that uses a coaxial cable to reverse the polarity of the pulse. The generator operates with "flying shields," i.e., high-voltage pulses also propagate on the outside of the cables; this calls for a dedicated insulation that avoids breakdown between sections of the cable's shield. The rise time obtained is mostly dictated by the switching time of the thyratron; with the one we used in the tests, rise times in the range of 30-40 ns were obtained. We present the results obtained in the implementation of the generators as well as its application to fire a large Marx generator.

Experimental Studies of an Axial Vircator with Different Cathode Geometries

Abstract: Summary form only given. This paper describes the numerical study and experimental results of an axial vircator with axial extraction. The microwave source is driven by a Marx generator and excludes any type of pulse forming device between the two subsystems. The main reason for this special arrangement is the final goal to build a compact and robust high power microwave system. The drawback is usually a lower efficiency of the microwave source. The vircator operates with the applied voltages between 200 and 400 kV and the impedance is around 50 Ohms during the process when microwave radiation is generated. The microwave pulse duration is for most cases between 50 to 100 ns. For the experiments described in this paper focus has been on different cathode geometries. Results that are given include microwave power, spectral content and mode characteristics. In an attempt to better understand and explain the experimental results particle-in-cell simulations have been carried out in MAGIC. These numerical results support to some extent the experimental results.

An asynchronous free-running arc, distributed energy railgun

Abstract: Summary form only given. Experimental results utilizing a distributed energy scheme and free-running arc are presented. Analysis and observations of the issues associated with distributed energy switching of a plasma armature in the railgun will be explored. The use of a free running arc allows experiments to emulate a plasma armature railgun at high speeds (> 5 km/s) without the requirement of a large amount of stored energy. Diagnostics for this examination include rail and plasma current probes as well as independent Rogowski coils for each stage. The distributed system is comprised of four stages spaced uniformly along the rail length. Each stage contains a high voltage capacitor, an inductor, a phase controlled SCR, and a driver board for triggering. The high voltage capacitors used are capable of storing 50 kJ, but are typically charged to store less than 20 kJ. Fiber optic lines are integrated into the system to prevent misfire in the noisy EMI environment. Optimal switch timing is predicted by a computer simulation and tested for accuracy. The assembled railgun is 2.4 m long with a 1.7 cm times 1.7 cm bore cross section. The rails are made of machined UNS C11000 ETP copper. G-10 insulation contains the current probes and separates the Aluminum 6061-T6 outer support structure from the rails. Alumina ceramic inserts are secured by the G-10 and function to reduce in-bore ablation. A PVC chamber encloses the railgun and allows experiments to be conducted within the desired 1-10 torr environment. A plasma source at the breech reliably supplies plasma for each experimental test. The plasma injector is powered by a Marx generator to supply a 40 kV voltage and pulse length of 10 s. The coaxial injector is comprised of a tungsten rod, ceramic insulator, and stainless steel outer casing. Numerous experimental tests were conducted to investigate the dynamics of plasma armatures within a distributed energy source railgun. Variations of switch timing, bore pressure, current amplitude, and current pulse length within each stage have been tested. This data is analyzed to determine the effectiveness of a distributed energy system to suppress the plasma restrike phenomenon and increase plasma armature railgun performance.

A 2.8 MV, 600 kA pulsed power driver constructed at the University of Missouri-Columbia

Abstract: Summary form only given. The University of Missouri has completed construction of a new facility for pulsed power experimentation. The pulsed driver is driven by a Marx bank consisting of 32, 100 kV, 3.1 muF capacitors. The Marx bank can store 450 kJ and is switched into any combination of one or up to four, parallel, 7 nF intermediate storage capacitors. The intermediate storage capacitors are switched with a high voltage spark gap switch into a resistive load. The driver is capable of delivering 2.8 MV at 600 kA to a 4 ohm load. Simulations indicate that the driver is capable of producing 1 MA through a load with lower impedance. Initial uses for the facility include experimentation on switch jitter and arc spectroscopy on a spark gap switch. The test results are also used in the characterization of the machine. Simulations of the driver capabilities are presented along with details of the initial results.