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Plasma Science, IEEE Transactions on

Issue 4  Part 1 • Date Aug. 2005

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  • Table of contents

    Page(s): c1 - 1133
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  • IEEE Transactions on Plasma Science publication information

    Page(s): c2
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  • High-Voltage Breakdown and Conditioning of Carbon and Molybdenum Electrodes

    Page(s): 1136 - 1148
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    Carbon and molybdenum electrodes employed in high-voltage devices such as ion sources and traveling wave tubes can be easily damaged by electrical breakdown and arcing events. Modification of the electrode surfaces due to these events can impact the voltage hold-off capability of the surfaces, which could lead to additional arcing, further damage, and the potential for device failure. Power supplies driving these devices are usually rated for their damage potential by the amount of stored energy. However, many systems that use arc discharges characterize the lifetime of the device for voltage hold-off and the amount of material removed from the surfaces by the amount of current that passes through the arc, or the “Coulomb-transfer rating.” The results of a series of tests that were performed on the voltage hold-off capability and damage to several different carbon and molybdenum surfaces due to induced arcing are presented. Damage to the surfaces was characterized by the field emission threshold after arcing events, by the amount of Coulomb-transfer in the arc, and by scanning electron microscope photographs of the subsequent surfaces. Both conditioning and damage to the surfaces were observed, and are related to the characteristics of the materials and the electrical breakdowns. View full abstract»

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  • DC and Pulsed Dielectric Surface Flashover at Atmospheric Pressure

    Page(s): 1149 - 1154
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    In a wide variety of high-voltage applications surface flashover plays a major role in the system's performance and yet has not been studied in great detail for atmospheric conditions with modern diagnostic tools. Environmental conditions to be considered include pressure, humidity, and gas present in the volume surrounding the dielectric. In order to gain knowledge into the underlying process involved in dielectric surface flashover, a setup has been created to produce and closely monitor the flashover event. Surface flashover for both direct current and pulsed voltages is considered. Within the setup, parameters such as geometry, material, and temporal characteristics of the applied voltage can be altered. Current, voltage, and luminosity are measured with nanosecond to sub-nanosecond resolution. Previously measured optical emission spectra is also discussed. View full abstract»

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  • High-Power RF Tests on X-Band Dielectric-Loaded Accelerating Structures

    Page(s): 1155 - 1160
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    A joint Argonne National Laboratory (ANL)/Naval Research Laboratory (NRL) program is under way to investigate X-band dielectric-loaded accelerating (DLA) structures, using high-power 11.424-GHz radiation from the NRL Magnicon Facility. DLA structures offer the potential of a simple, inexpensive alternative to copper disk-loaded structures for use in high-gradient radio-frequency (RF) linear accelerators. A central purpose of our high-power test program is to find the RF breakdown limits of these structures. In this paper, we summarize the most recent tests results for two DLA structures loaded with different ceramics: alumina and$ Mg_ x Ca_1- x TiO_3$(MCT). No RF breakdown has been observed up to 5 MW of drive power (equivalent to 8 MV/m accelerating gradient), but multipactor was observed to absorb a large fraction of the incident microwave power. The latest experimental results on suppression of multipactor using a TiN coating on the inner surface of the dielectric are reported. Although we did not observe dielectric breakdown in the structure, breakdown did occur at the ceramic joint, where the electric field is greatly enhanced. Lastly, the MCT structure showed significantly less multipactor for the same level RF field. View full abstract»

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  • The Impact of Surface Conditioning and Area on the Pulsed Breakdown Strength of Water

    Page(s): 1161 - 1169
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    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. View full abstract»

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  • Designing Pulse Power Generators

    Page(s): 1170 - 1176
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    When the performance criteria for a pulsed power generator is power density, and the duty cycle remains short ($≪ , 20$s), then copper coils with an exciter are favored over permanent magnet rotors. If the permanent magnets are replaced with copper coils, steel, and an exciter, with the same total weight, the copper coil alternative will return a higher magnetomotive force/weight, and thus a higher power density system. A variable metric optimization is completed for a generator, assuming the objective is to charge a capacitor bank. The equations governing allowed current density in capacitor charging applications and alternating current/direct current (ac/dc) resistance ratios are derived. View full abstract»

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  • Compact High Repetition Rate Pseudospark Pulse Generator

    Page(s): 1177 - 1181
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    A pseudospark-based high repetition rate pulse generator, together with a resonant charging power supply is presented. The pulse generator was developed for research applications that include transient plasma ignition. The design incorporates a lumped element Blumlein pulse-forming network that is switched by a commercial pseudospark into an output pulse transformer with a METGLAS core. The Blumlein is charged up to 30 kV by a resonant capacitor charger, based on a fly-back transformer and high-power insulated gate bipolar transistor (IGBT) switch module. The output voltage of the charger is controlled by the on-time of the IGBT. Pulses with duration of 50 ns can be generated at a 2.6-kHz maximum repetition rate. Pulses with amplitude up to 90 kV can be delivered into a 200-$Omega $load. View full abstract»

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  • A High Repetition Rate Nanosecond Pulsed Power Supply for Nonthermal Plasma Generation

    Page(s): 1182 - 1185
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    The basic principles of high repetition rate nanosecond pulsed power supplies, the design, and the implementation are presented. Voltage pulses of 20–30 kV with a rise time of 30 ns, a pulse duration of 200 ns, a pulse repetition rate of 1–2 kHz, an energy per pulse of 0.5–1 J, and the average power up to 0.5–1 kW have been achieved with total energy conversion efficiency of 90%. The protective circuit against overvoltage and the measurement of high-voltage output are described. View full abstract»

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  • A Compact Former of High-Power Bipolar Subnanosecond Pulses

    Page(s): 1186 - 1191
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    The system comprises either a nanosecond solid-state operating switch (SOS)-generator (see, e.g., Rukin, 1995) or a RADAN pulsed power source (see, e.g., Mesyats , 1993) that charges resonantly a short pulse-forming line (PFL) through a decoupling inductor, an active converter, a matched load, and several built-in voltage and current probes. The active converter comprises an additional 1-ns PFL charged through a peaking spark gap (SG) and a secondary decoupling inductor by the first PFL, and two SGs (chopping and peaking gap). The peaking SG and active converter are set in one body and operate in$ N _2$at pressure up to 6 MPa. Driven by RADAN, the converter generates bipolar subnanosecond pulses having peak-to-peak amplitude up to 270 kV across 46.6-$Omega $load. The pulsewidth of each half wave of bipolar pulses on full-width at half-maximum is 280 ps, with the risetime of the first half wave of about 160 ps. The SGs' gaps can be regulated without system depressurizing (a technique adopted from Shpak , 1996). Circuit analysis accounting for the distributed character of the components and numerous parasitic parameters is presented. Mapping of main SG parameters (gap distance and pressure) was performed. Waveforms probed at different locations of the pulser systems, from the SOS-generator and from the RADAN to the load, are shown. The bipolar subnanosecond pulses had very stable rise, while the fall jitter was around 50 ps. The experimental results are in fair agreement with the simulation. Pulsers were tested with a transverse electromagnetic horn antenna. An effective potential of 910 kV was obtained. View full abstract»

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  • Nanosecond Pulse Generator Using Fast Recovery Diodes for Cell Electromanipulation

    Page(s): 1192 - 1197
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    Design and operation of a fast recovery diode based pulse generator is presented. The generator produces 3.5-ns-wide, 1200 V amplitude unipolar pulses or$+/-600$-V bipolar pulses into 50-$Omega$load at the maximum repetition rate of 100 kHz. Pulses shorter than 10 ns are essential for the studies of biological cell response to high electric fields while avoiding ordinary electroporation effects dominant at long pulses. Bipolar pulses are used for the studies of biological cell response to high electric fields when the net transfer of charge is undesirable. The bipolar pulse is produced from a unipolar pulse with the help of a shorted transmission line. This transmission line delays and inverts the initial pulse, so the output is the sum of the initial and the inverted and delayed pulses. The use of mass-produced fast recovery surface-mount rectifier diodes in this circuit substantially simplifies the generator and results in low cost and very small footprint. Similar diode switched pulse generators have been described in the literature using mostly custom fabricated snap-recovery diodes. Here we give an example of an ordinary low-cost diode performing similarly to the custom fabricated counterpart. The diode switched circuit relaxes the requirement on the speed of the main closing switch; in our case, a low-cost power metal-oxide semiconductor field-effect transistor (MOSFET)–saturable core transformer combination. View full abstract»

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  • Solid State Marx Generator Using Series-Connected IGBTs

    Page(s): 1198 - 1204
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    This paper describes a newly developed novel repetitive impulse voltage generator using a boost converter array. To solve problems such as short life time, low operating frequency, and the fixed pulse width of conventional generators, the proposed generator is designed with a boost converter array that employs series-connected capacitors and insulated gate bipolar transistors. The circuit can easily obtain a high-voltage pulse without any high-voltage direct current source and pulse transformer. Thus, the proposed circuit not only allows elimination of the expensive high-frequency transformer but also allows operation at a frequency up to several kilohertz with high reliability and longer life span. To validate the proposed circuit, two pulse generators rated at 1.8 kV, 40 A and 20 kV, 300 A are implemented and tested. View full abstract»

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  • Novel Dual Marx Generator for Microplasma Applications

    Page(s): 1205 - 1209
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    Micrometer size plasmas, or microplasmas, find applications in pollution control, reduction, and prevention. The required nonthermal plasmas can be generated by either an electron beam or an electric discharge. The pulse widths and voltages necessary to generate these nonthermal plasmas are$10 ^-10$$10 ^-8~ s$, and$10 ^3$$10 ^4~ V$, respectively, depending on the application. The required energy is typically in the low$10 ^-3~ J$range. This paper presents a novel circuit design to generate high-voltage pulses with variable pulse widths and pulse rise and fall times in the low$10 ^-9~ s$regime. The circuit employs two parallel Marx Generators utilizing bipolar junction transistors (BJTs) as closing switches. The BJTs are operated in the avalanche mode to yield fast rise times. The design allows for positive or negative polarity pulses, and can easily be changed to yield higher or lower output voltage. View full abstract»

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  • High-Frequency Multimegawatt Polyphase Resonant Power Conditioning

    Page(s): 1210 - 1219
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    High-frequency multimegawatt polyphase resonant power conditioning techniques have recently been realized as a result of key component developments, cooperative efforts, research and development funding contracts, and newly applied engineering techniques. The first generation 10-MW pulsed converter-modulators, implemented at Los Alamos National Laboratory, Los Alamos, NM, are now utilized for the Oak Ridge National Laboratory, Oak Ridge, TN, Spallation Neutron Source (SNS) accelerator klystron radio frequency amplifier power systems [1]. Three different styles of polyphase resonant converter-modulators were developed for the SNS application. The various systems operate up to 140-kV, or 11-MW pulses, or up to 1.1 MW average power, all from a direct current input of$+/-$1.2 kV. The component improvements realized with the SNS effort coupled with new applied engineering techniques have resulted in dramatic changes in overall power conditioning topology. As an example, the 20-kHz high-voltage transformers are less than 1% the size and weight of equivalent 60-Hz versions. With resonant conversion techniques, load protective networks are not required. A shorted load de-tunes the resonance which results in limited power transfer. This provides for power conditioning systems that are inherently self-protective, with automatic fault “ride-through” capabilities. By altering and iterating the Los Alamos design, higher power and continuous wave power conditioning systems can now be realized with improved performance and flexibility. This paper will examine the SNS engineering data, briefly review the underlying theory of polyphase resonant conversion techniques, and apply this knowledge to future system topologies. View full abstract»

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  • Nanosecond Hybrid Modulator for the Fast-Repetitive Driving of X-Band, Gigawatt-Power Microwave Source

    Page(s): 1220 - 1225
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    Results of tests of a fast-repetitive nanosecond modulator with a peak output power of 3 GW are presented. It comprises of a type S-5N charging driver, a power compressor based on a pulsed forming line, and a gas spark gap. The modulator has been designed for the formation of high-current electron beams and high-power microwave generation in a pulsed-repetitive regime. Excitation of 10-GHz microwave pulses$sim1$ns long in a relativistic backward-wave oscillator with an elongated periodic slow-wave system has been studied. Optimization of the regime of interaction between electromagnetic fields and particles provided an average power of microwave radiation in the burst-repetitive mode (1 s;$sim700$Hz) of up to 2.5 kW at a focusing magnetic field ($sim0.6$T) below the cyclotron resonance region. The peak output power of the oscillator exceeded 2 GW. View full abstract»

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  • Thermal and Electrical Evaluation of SiC GTOs for Pulsed Power Applications

    Page(s): 1226 - 1234
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    For applications which require high peak current and fast rise time, silicon carbide (SiC) material is ideal because of its ability to tolerate high localized temperatures generated during switching. This research was performed to investigate SiC devices for pulse power applications and to analyze the failure of the devices. Seven 2 mm$,times,$2 mm SiC gate turn-off thyristors (GTOs) manufactured by Cree, Inc., Durham, NC, were evaluated. The devices were tested at single shot and under repetitive stress using a ring-down capacitor discharge circuit. The current pulsewidth was 2$muhbox s$with a peak current of 1.4 kA (current density of 94.6$ kA/hbox cm^2$) and a maximum$di$/$dt$of 2.36$ kA/muhbox s$. The maximum power dissipated within the devices was 240 kW. Thermal modeling of these devices was done using ANSYS to analyze the heating and cooling. A two-dimensional model was used that included the device package and bonding materials. The maximum amount of power dissipated was calculated from the 1000-A, 2-$muhbox s$pulse. No further power input was added to the model and the heat transfer was plotted on an exponential scale. It was found that heat applied to a 2-$muhbox m$-thick region of the fingers yielded a temperature greater than 800$^circ hbox C$in the device. It took$1.0 E ^-02$s for this heat to dissipate and for the device to return to 23$^circ hbox C$. The minimum and maximum stresses were found to be$-2.83 E ^+09~ Pa$and$4.06 E ^+08~ Pa$, respectively. View full abstract»

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  • Preliminary Evaluation of Super GTOS in Pulse Application

    Page(s): 1235 - 1239
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    Compact high-action solid state switches are essential to weapon and protective systems for future Army vehicles. The Army Research Laboratory, Adelphi, MD, has been evaluating conventional and unconventional devices for an extended period of time. Large diameter thyristors have been explored and evaluated at currents in excess of 200 kA. Reverse dynistors, a Russian device, have shown even better performance than conventional thyristors due to their very fine gate structure (10–100s of microns). Fine gate structure leads to faster turnon, so that the switch is in full conduction much faster than those with more conventional gates, which vastly improves the reliability and lifetime of such devices. Silicon power corporation (SPCO) has produced a thyristor with an even finer gate structure than the dynistor. This super GTO (SGTO) also differs from conventional high-current thyristors in that it is modular rather than a single wafer design. Aside from a potential reduction in cost due to improved yield, the SGTO may be easily configured to produce the desired level of peak current by adding or subtracting individual chips in the module. This year, the Army Research Laboratory will obtain the first 400-kA SGTOs, which is double the prior current carrying capability of previous single wafer thyristors. A more critical parameter will be an increase of di/dt on turn-on by an order of magnitude. Single wafer thyristors of large diameter have had di/dt measured in kA/us. The objective of the SGTO switch is in excess of 40 kA/us. This paper presents the first experimental data from a prototype device, rated at 80-kA peak current. Data from this round of evaluation will provide critical design data for the realization of switch modules of 400 kA and beyond. View full abstract»

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  • High-Power Semiconductor-Based Nano and Subnanosecond Pulse Generator With a Low Delay Time

    Page(s): 1240 - 1244
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    One of the promising designs of high-power nanosecond and subnanosecond pulse generators is based on the fast ionization dynistor (FID) stack triggered with nanosecond pulse of overvoltage. This pulse is usually formed by semiconductor opening switches. Delay time of these switches equals the sum of forward and reverse current pulse duration, i.e., several hundreds of nanoseconds. The novel opening switch, inverse recovery diode (IRD), is capable of forming a nanosecond pulse of voltage with the delay time equal to the reverse current pulse duration (15–20 ns) due to the special diode structure. High-voltage nanosecond pulse formed with IRD is used for fast triggering of the first FID from high-voltage dc-biased FID stack. The resulting fast overvoltage pulse is applied to the second FID, etc. As a result, the high-voltage FID-stack is switched for units of nanosecond. Total delay time of IRD-FID-based pulse generators is less than 30 ns. View full abstract»

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  • Modeling and Analysis of the Rimfire Gas Switch

    Page(s): 1245 - 1251
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    Many accelerators at Sandia National Laboratories utilize the Rimfire gas switch for high-voltage, high-power switching. Future accelerators will have increased performance requirements for switching elements. When designing improved versions of the Rimfire switch, there is a need for quick and accurate simulation of the electrical effects of geometry changes. This paper presents an advanced circuit model of the Rimfire switch that can be used for these simulations. The development of the model is shown along with comparisons to past models and experimental results. View full abstract»

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  • Analysis of High-Power IGBT Short Circuit Failures

    Page(s): 1252 - 1261
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    The next linear collider (NLC) accelerator proposal at Stanford Linear Accelerator Center (SLAC, Menlo Park, CA), requires a highly efficient and reliable, low cost, pulsed-power modulator to drive the klystrons. A solid-state induction modulator has been developed at SLAC to power the klystrons; this modulator uses commercial high voltage and high current insulated gate bipolar transistor (IGBT) modules. Testing of these IGBT modules under pulsed conditions was very successful; however, the IGBTs failed when tests were performed into a low inductance short circuit. The internal electrical connections of a commercial IGBT module have been analyzed to extract self- and mutual partial inductances for the main current paths as well as for the gate structure. The IGBT module, together with the partial inductances, has been modeled using PSpice. Predictions for electrical paths that carry the highest current correlate with the sites of failed die under short circuit tests. A similar analysis has been carried out for a SLAC proposal for an IGBT module layout. This paper discusses the mathematical model of the IGBT module geometry and presents simulation results. View full abstract»

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  • Critical Component Requirements for Compact Pulse Power System Architectures

    Page(s): 1262 - 1267
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    The fundamental limits on the volume and energy density of a pulse power that is to deliver a specific peak power pulse to a load depends upon the architecture of the system, the operational mode of the system, the energy storage geometries, the switching parameters employed, and the auxiliary equipment required. This paper examines these factors and develops the fundamental limits on the volume of a pulse power system for a given output pulse energy and pulse length. The fundamental limits on power density lead to the selection of an optimum architecture, which leads to critical specifications for the components involved. This paper develops and presents those specifications for the major components in a pulse power system with maximum power density. Two prototype systems, a short pulse (50 ns) system and a long pulse (1$mu s$) system, are designed as examples of the optimum pulse power architecture and the resulting component requirements. View full abstract»

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  • Field Enhancement Optimization of an Air-Cored Spiral Strip Pulse Transformer

    Page(s): 1268 - 1272
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    The structure of a compact air-cored high-voltage spiral strip pulse transformer is relatively simple, but considerable attention is needed to prevent breakdown between transformer windings. Since thickness of the winding conductors in the spiral strip type is in the order of submillimeter, field enhancement at the edges of the winding conductor is very high. It is, therefore, important to find proper winding parameters to reduce the field enhancement and, thus, to make the system compact. An insulator structure, which has multilayered dielectric materials with different dielectric constants, has been considered and numerically simulated. The field enhancement factor has been defined and obtained as a function of the conductor edge shape, dielectric constants of the insulation layer, and the thickness of multilayered dielectric material. Optimum design parameters are obtained to reduce the field enhancement at the edge of the windings. View full abstract»

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  • ZR Marx Capacitor Vendor Evaluation and Lifetime Test Results

    Page(s): 1273 - 1281
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    The Z machine at Sandia National Laboratories (SNL) is the world's largest and most powerful laboratory X-ray source. The Z Refurbishment Project (ZR) is presently underway to provide an improved precision, more shot capacity, and a higher current capability. The ZR upgrade has a total output current requirement of at least 26 MA for a 100-ns standard Z-pinch load. To accomplish this with minimal impact on the surrounding hardware, the 60 high-energy discharge capacitors in each of the existing 36 Marx generators must be replaced with identical size units but with twice the capacitance. Before the six-month shut down and transition from Z to ZR occurs, 2500 of these capacitors will be delivered. We chose to undertake an ambitious vendor qualification program to reduce the risk of not meeting ZR performance goals, to encourage the pulsed-power industry to revisit the design and development of high- energy discharge capacitors, and to meet the cost and delivery schedule within the ZR project plans. Five manufacturers were willing to fabricate and sell SNL samples of six capacitors each to be evaluated. The 8000-shot qualification test phase of the evaluation effort is now complete. This paper summarizes how the 0.279$,times,$0.356$,times,$0.635-m (11$,times,$14$,times,$25-in) stainless steel can, Scyllac-style insulator bushing, 2.65-$mu F$,$≪30mathchar"702D nH$, 100-kV, 35%-reversal capacitor lifetime specifications were determined, briefly describes the nominal 260-kJ test facility configuration, presents the test results of the most successful candidates, and discusses acceptance testing protocols that balance available resources against performance, cost, and schedule risk. We also summarize the results of our accelerated lifetime testing of the selected General Atomics P/N 32896 capacitor. We have completed lifetime tests with twelve capacitors at 100 kV and with fourteen capacitors at 110-kV charge voltage. The means of the fitted Weibull distributions for these two cases are about 17 000 and 10 000 shots, respectively. As a result of this effort plus the rigorous vendor testing prior to shipping, we are confident in the high reliability of thes- e capacitors and have acquired information pertaining to their lifetime dependence on the operating voltage. One result of the analysis is that, for these capacitors, lifetime scales inversely with voltage to the$6.28 pm 0.91$power, over this 100 to 110-kV voltage range. Accepting the assumptions leading to this outcome allows us to predict the overall ZR system Marx generator capacitor reliability at the expected lower operating voltage of about 85 kV. View full abstract»

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  • RF Accelerator Controlled by High Accuracy RF Phase Detector

    Page(s): 1282 - 1286
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    Radio frequency (RF) phase detector in 2856 MHZ based on personal computer is designed, built, and tested in support of free electron laser development based on 200-MeV RF linear accelerator in National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, which means for Chinese middle and long term development programme for basic research. The tested resolution of the designed RF phase detector in 2856 MHZ is better than 0.3$^circ$. The potential applications of the high accuracy RF phase detector in RF linear accelerators and free electron laser are given. View full abstract»

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Aims & Scope

IEEE Transactions on Plasma Sciences focuses on plasma science and engineering, including: magnetofluid dynamics and thermionics; plasma dynamics; gaseous electronics and arc technology.

 

 

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Meet Our Editors

Editor-in-Chief
Steven J. Gitomer, Ph.D.
Senior Scientist, US Civilian Research & Development Foundation
Guest Scientist, Los Alamos National Laboratory
1428 Miracerros Loop South
Santa Fe, NM  87505  87505  USA
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