Showing papers on "Marx generator published in 2001"

The Marx generator as an ultra wideband source

Abstract: Summary form only given. Traditional uses of the Marx generator have been limited to energy storage and delivery systems, such as charging capacitors or pulse forming lines. However, low energy, high peak power Marx generators are finding applications in Ultra Wideband radar and high power microwave systems. This paper presents the results of a new compact, high powered Marx generator designed for these applications. The pulse parameters of the generator are discussed, as well as radiation measurements made with TEM horn antennas.

An ultra-compact Marx-type high-voltage generator

Abstract: This paper discusses the design of an ultra-compact, Marx-type, high-voltage generator. This system incorporates high-performance components that are closely coupled and integrated into an extremely compact assembly. Low profile, custom ceramic capacitors with coplanar extended electrodes provide primary energy storage. Low-inductance, spark-gap switches incorporate miniature gas cavities imbedded within the central region of the annular shaped capacitors, with very thin dielectric sections separating the energy storage capacitors. Carefully shaped electrodes and insulator surfaces are used throughout to minimize field enhancements, reduce fields at triple-point regions, and enable operation at stress levels closer to the intrinsic breakdown limits of the dielectric materials. Specially shaped resistors and inductors are used for charging and isolation during operation. Forward-coupling ceramic capacitors are connected across successive switch-capacitor-switch stages to assist in switching. Pressurized SF/sub 6/ gas is used for electrical insulation in the spark-gap switches and throughout the unit. The pressure housing is constructed entirely of dielectric materials, with segments that interlock with the low-profile switch bodies to provide an integrated support structure for all of the components. This ultra-compact Marx generator employs a modular design that can be sized as needed for a particular application. Units have been assembled with 4, 10, and 30 stages and operated at levels up to 100 kV per stage.

Multi gap switch for Marx generators

Abstract: Summary form only given, as follows. The report presents new gas switch for Marx generators with by polar charging up to 100 kV. The trigger electrode divides the switch into two parts (positive and negative), each of these parts includes three intermediate electrodes. The charge voltage between the intermediate electrodes is evenly distributed by corona discharge. This allows to obtain safe operation of the switch being filled with air at a pressure up to 3 atm. The report presents the design of the switch and test results on a test bed (32 kJ, 320 kA) and in the Marx generator.

Sub-nanosecond jitter operation of Marx generators

Abstract: Summary form only given, as follows. Low energy, high peak power Marx generators are finding applications in ultra wideband radar and high power microwave systems. In many cases, these systems require very precise control over the delivery of the pulse from the generator. For example, two individual generators might be used for bi-static radar. Temporal jitter between the two generators may add ambiguity to the measurement. A 17 stage Marx generator was fabricated to study techniques for reducing the jitter in a multi-spark gap system. This paper presents the results of a jitter study, as well as methods explored for jitter reduction.

Determining Ideal Impulse Generator Settings from a Generator-Transformer Circuit Model

Abstract: Impulse testing of large power transformers is a routine test, which is designed to mimic a lightning strike in service. At the design stage, it is useful to have a detailed circuit model of the transformer in order to simulate the impulse test and to check for possibly damaging voltage stress levels. In the authors' model, which includes capacitive and inductive couplings, as well as resistive effects, they apply an ideal full or chopped waveform to the impulsed terminal. In an actual impulse test, it is sometimes difficult to approximate the ideal waveform, particularly the full-wave one, and a trial-and-error approach is often taken. Here, they describe an approach that couples a circuit model of the impulse generator with a transformer circuit model and show how, from this combination, they can arrive at close to ideal settings for the generator, provided such settings are possible.

Ultrafast LTD's for bremsstrahlung diodes and Z-pinches

Abstract: Most of the modern high-current high-voltage induction linacs require several stages of pulse conditioning (pulse forming) to convert the multi-microsecond pulses of the Marx generator output to the 40-100 ns pulse required for a cell cavity. This makes the devices large, cumbersome to operate, and expensive. In the present design we eliminate Marxes and pulse-forming networks and instead utilize a new technology recently implemented at the Institute of High Current Electronics in Tomsk (Russia). Each inductive voltage adder cavity is directly fed by a number of fast 100-kV small-size capacitors arranged in a circular array around each accelerating gap. The number of capacitors connected in parallel to each cavity defines the total maximum current. By selecting low inductance switches, voltage pulses as short as 30-60-ns FWHM can be directly achieved. The voltage of each stage is low (100-200 kV). Many stages are required to achieve multi-megavolt accelerator output. However, since the length of each stage is very short (4-10 cm), accelerating gradients of higher than I MV/m can easily be obtained. Each LTD voltage adder can deliver up to 1-MA current to the load. To produce drivers of higher current, many LTD's are connected in parallel. A conceptual design for Saturn three ring diode and Z-pinch and a compact 10-MV 100-kA 60-ns accelerator for advanced radiography will be presented. In both designs the LTD's operate in vacuum and no liquid dielectrics like oil or deionized water will be required. Even elimination of ferromagnetic material (air-core cavities) is a possibility. This makes the devices cheaper, smaller, and lighter than the devices presently utilized which are based on conventional pulsed power technology architecture. We envisage a factor of 3 reduction in size and cost.

Design options for a pulsed-power upgrade of the Z accelerator

Abstract: We are presently considering an extensive modification of the Z accelerator at the Sandia National Laboratories to both increase the current and radiative power, and to improve the facility, diagnostics, and shot rate. Record-breaking peak x-ray powers and Hohlraum temperatures achieved in z-pinch experiments on this machine motivate this effort. The electrical design goal of the upgrade is to drive a 40-mm diameter, 20-mm long wire-array z-pinch load with a peak current of 26 MA with a 100-ns implosion. Several changes to the pulsed-power design of Z are being considered. They are to increase the energy and lower the inductance of the Marx bank, increase the capacitance of the intermediate-store water capacitor, increase the voltage hold-off capability of the laser-triggered gas switch, lengthen the first section of the water pulse-forming line, remove impedance mismatches in the pulse-forming line, and adjust field grading on the water side of the insulator stack. With these changes Z will be able to provide peak currents greater than 26 MA, and x-ray energies exceeding 2.7 MJ. We plan to use the existing oil and water tanks, use the existing insulator stack and MITL's, and as much of the existing Marx-bank hardware as feasible. Circuit-code calculations for one design option are shown. The results of these simulations, when applied to standard water-breakdown criteria, are used to determine the size of the intermediate store (IS) and pulse-forming-line (PFL) components. We also indicate where further component development is needed.

Trigger circuit for Marx generators

Abstract: A trigger circuit is provided for a trigger system for a Marx generator column. The column includes a plurality of metal electrode pairs wherein the electrodes of each pair are spaced to form a spark gap therebetween and a capacitor is connected across each gap. The trigger system includes a three electrode (trigatron) spark gap switch forming the first spark gap of the Marx generator column. The triggering circuit includes a trigger transformer having primary and secondary windings. The secondary winding is connected through a connecting cable to a blocking capacitor of an input circuit of the trigatron switch. A charging capacitor is connected to an oscillator power supply so as to be charged thereby to the output voltage (e.g., 345 volts) of the oscillator power supply. An electronic switch (e.g., an SCR) is connected to a junction between the charging capacitor and the oscillator power supply for, when actuated by an input pulse, completing a connection between the capacitor and the primary winding of the trigger transformer so that a high voltage trigger pulse is produced at the secondary winding of the trigger transformer.

Tests of 6-MV triggered switches on APPRM at SNL

Abstract: Summary form only given. The Advanced Pulsed Power Research Module (APPRM) was created at Sandia National Laboratory (SNL) to serve as a test bed for the development of pulsed power technologies and components that could be used in future generation high power facilities. In the present configuration the test bed is comprised of a 56 stage, 850-kJ Marx generator that charges a 5.5-Ohm water insulated Intermediate Storage Capacitor (ISC) to more than 7 MV in /spl sim/1.5 us. The switches tested were located at the output end of the ISC where they connected the output to a 5.5-Ohm CuSO/sub 4/ resistive load. Several switches have been tested on APPRM. The first switch tested was an evolved version of the Sandia designed HERMES III switch. It consists of self-breakdown (cascade) section where the discharge current flows in several parallel channels, and a trigger section where the current flows through a single spark channel. The second switch tested was a Russian/Sandia Hybrid switch. The trigger section of the Hybrid switch, designed at High Current Electronics Institute (HCEI) in Tomsk, Russia, includes six HCEI composite electrodes connected in parallel to a triggered gap via a 4-uH series isolation inductor. The discharge current in the Hybrid switch trigger section flows in several parallel channels eliminating the single channel flow as in the Sandia switch trigger section. The last switch tested is a HCEI switch design where the trigger and cascade sections are comprised of HCEI composite electrodes. The design of the switches and results of these tests will be presented as well as the analysis and comparison of results.

Compact battery-powered, 400-kV, 40-Joule Marx generator

Abstract: The experimental results of a compact, portable, battery-powered, 400 kV, 40 Joule Marx Generator are presented. The Marx Generator, high voltage power supplies, batteries, and the remote fiber optic high voltage enable and trigger control circuits are all contained in an aluminum tube measuring 5 inches in diameter and 20 inches in length. The space within the tube is divided into the Marx Generator section and the power supply section. The Marx Generator section is completely modular and can be easily unplugged to facilitate repair or exchange. The use of non-encapsulated, 22 nF, 10 kV surface-mount chip capacitors, mounted to a printed circuit board together with the charging resistors, resulted in a very compact assembly. The capacitors and charging resistors are potted in a dielectric gel while the spark gaps are independently insulated with SF/sub 6/ and aligned in a line-of-sight configuration for UV coupling. The entire Marx Generator assembly is packaged in a Lucite tube approximately 10 inches in length, which can be pressurized to 50 psi. Repetition rates of 1 pps and rise times of 20 ns are typical.

Fast Marx Generator development for PRS drivers

Abstract: Design studies for a full threat simulator to drive PRS implosions to around 50 MA in 250 ns showed the importance of Fast Marx Generators (FMGs) with intrinsic discharge times (LC)/sup 1/2 / significantly less than the present state-of-the-art in large machines (e.g. /spl gsim/500 ns in the SNL "Z"). Energy, size, complexity, and therefore cost are significantly reduced, and the need for intermediate stages of power gain are eliminated as FMG discharge time approaches an optimum (around 125 ns for 250 ns implosions). We describe designs for 175 ns and 300 ns FMGs and specific components that are being developed for use in large systems. This FMG technology development builds in part on that of systems built by the USA DoD in the 1970s and 1980s, which are also summarized. This technology can be applied to either of the fast Marxes and to the LTD described by P. Corcoran et al. (see ibid., p.577-81, 2002) and to upgrades of existing systems such as the Z refurbishment.

Nanosecond, kilovolt pulse generators

Abstract: Nanosecond pulse generators, which provide kilovolt pulses, are required for applications such as pulsed lasers, electro-optical devices, electron heating of plasmas, and bioelectrics. Switches used to generate such short pulses include high-pressure spark gaps, photoconductive switches and semiconductor opening switches. Most of the pulse generators based on these switch technologies are designed for high voltage, high power applications. We have explored two concepts that of a MOSFET triggered, microspark Marx-Bank and a combined microspark-semiconductor switch system as a means to generate simple, inexpensive nanosecond pulse generators. The compact pulse generators allow us to generate electrical pulses of less than 10 ns duration, with amplitudes of several kV. The Mini Marx Bank has been shown to provide 6 kV pulses of 6 ns duration into a 10 M/spl Omega/ load and 2 kV into a 50 /spl Omega/ load. The second switch system, which utilizes a microspark switch and a commercially available diode to shorten the pulse, has provided 2.6 kV pulses of 2 ns duration into a 50 /spl Omega/ load. The low cost of the generator components, and the compact size make these devices easy to built and convenient to use in nanosecond pulsed power experiments.

Prototype IVA module (PIM)

Abstract: As a result of the Pulsed Power Group's programme to gain expertise in IVA (inductive voltage adder) technology we have designed a prospective module for a future large IVA machine that would be suitable for full scale radiography at AWE. This machine would operate at 13 to 15 MV. The PIM machine has been built at AWE to test a single such module and we have been collecting performance data from it before fixing the design for the full size machine. PIM also provides the basis for the PPG's continued research programme in this area and hence possible other machines for the future. The PIM machine consists of a single inductive cavity pulsed by a water dielectric Blumlein pulse forming line which is charged by a Marx generator. The Marx generator is based on the Sandia hanging Marx design. It is constructed using 32 1.35 uF 100 kV DC capacitors. The Marx pulse charges the 10 ohm water Blumlein. which acts as a fast pulse forming section. The Blumlein switch initially installed was a co-axial two stage rimfire and trigatron switch. A laser triggering configuration utilising two radial switches, designed by Titan PSI, is also to be tested. The inductive cavity incorporates ferromagnetic cores formed from Metglas alloy tape and the fast pulse appears across a perspex (lucite) insulated accelerating gap. The pulse travels along a short vacuum transmission line to a ball/plane e-beam diode test load. Work has been carried out to test the module design. Initially the Marx was characterised into a resistive load to establish its operating regime. The Blumlein PFL and its Rimfire/Trigatron switch were then tested, also using a copper sulphate load. A peak output voltage of 1.7 MV was achieved from the PFL. The inductive cavity has been added and we are in the process of testing it. A pulse of 1.4 MV peak voltage has been successfully applied to it. The latest details of the system's characterisation are presented.

Energy balance of the TW pulsed power generator Kalif-Helia

Abstract: Summary form only given. KALIF-HELIA is a TW pulsed power generator based on the high energy linear induction adder principle. At nominal conditions-i.e. 95 kV charge voltage of the Marx generator-it should produce an electrical pulse with a fwhm of 50 ns, a peak voltage and current of 6 MV and 400 kA respectively. Based, on transmission line calculations the estimated pulse energy into a 15 Ohm load is from 110 to 130 kJ, depending on the switch-out timing of the PFL water switches. The energy stored in the Marx generator charged to 95 kV is 357 kJ. For negative polarity operation the beam energy produced by an electron diode was achieved from electrical measurements and from calorimeter data. Both consistently showed beam energies of typically 60 kJ. Possible reasons for this unexpectedly low beam energy may be losses due to:- the energy transfer from the Marx generator to the intermediate stores-the switching characteristics of the gas- and/or water switches-pulse synchronization problems related to spread of the gas-and/or water switches-insulation properties of the cores of the induction cells-the magnetically insulated voltage adder and/or the vacuum transmission line In this paper the energy losses will be discussed on-basis of extensive measurements performed on KALIF-HELIA and recent results from detailed transmission line code calculations.

The Gatling Marx generator system

Abstract: Summary form only given, as follows. Traditional multi-pulse systems require multiple uncoupled sources, each driving a unique load. A phased array system, for example, may use multiple sources, each with its own antenna element, to radiate multiple pulses to a target. However, the Injection Wave Generator (IWG) has brought the concept of coupling multiple sources with a single load transmission line. Thus, multiple sources may be used to drive a single load element. In the case of a radar source, the overall volume of the system may be drastically reduced with only one antenna required. The paper discusses a Marx generator-based IWG system designed to deliver multiple high voltage pulses to a single load. The pulse magnitudes are on the order of several hundred kV, and with a pulse separation of 10 s of nanoseconds. The system is described with an emphasis on the results of the experimental system. Radiation results, with the Gatling system driving a single TEM horn antenna are presented and discussed.

Study of plasma evolution in argon-filled capillary Z-pinch devoted to x-ray production

Abstract: The high-current (up to 40 kA) fast electrical discharge Z-pinch in an argon-filled capillary has been developed to produce pulses of intense soft x-ray radiation in the spectral region of 2-50 nm. We present results of an experimental analysis of plasma evolution in the Z-pinch and discuss them in comparison with a theoretical model. The effects of the electrical circuit parameters and the initial discharge conditions on the plasma evolution are studied. The current was produced by a water dielectric capacitor (C = 3 or 10 nF) resonantly charged to the selected voltages (up to 450 kV) by a six-stage Marx generator. The current pulse with amplitude ranging from 20 to 40 kA and a half-cycle duration of 90 or 170 ns was generated through a 14.5 cm long, 5 mm diameter Al2O3 ceramic channel. The capillary was filled by argon to a selected pressure in the region 0.1-1 Torr. The experimental results are in good agreement with the predictions of the so-called `simple model of Z-pinch'.

Factors affecting the pulse width of capillary discharge soft X-ray laser

Abstract: Summary form only given, as follows. There are two ways to realize the population inversion in capillary discharge soft X-ray lasers: electron-collisional recombination pumping and electron-collisional excitation pumping schemes. It is possible to enhance the output of laser energy by increasing the gain-length product and the laser pulse width. While the former scheme can extract laser pulses of several tens of ns, the latter scheme can extract only several ns. Pulse widths are determined by the preservation time of optimal plasma condition and the growth time of plasma instability. The object of our study is to reveal the cause which restricts the duration of lasing in the collisional excitation scheme. The device consists of a Marx generator, a pulse transformer, a speed-up capacitor, a gap switch, a capillary and a pre-discharge circuit. The capillary is made of Pyrex glass and is 60 mm in length and 3 mm in inner diameter and is filled with an argon gas of 100-1000 mTorr. Uniformly pre-ionized argon gas in the capillary is excited with the current pulse having an amplitude of 15-60 kA and a first half cycle duration of 100 ns. The plasma photographs were taken from the side and axial directions using a high-speed camera in order to confirm its pinch and the growth of instability. The temporal evolution of the laser energy was measured with a vacuum X-ray diode. The duration of lasing is discussed based on the results of these experiments and MHD simulations of the imploding plasma.

Design of a new driver for fast capillary discharge

Abstract: A new driver of the fast capillary discharge is designed. It consists of the Marx generator and radial Blumline pulse forming line. Such a geometry enables axial access to both capillary ends (transparent capillary). This substantially simplifies the experiments (adjustment, monitoring, applications). The designed apparatus is capable to reach the discharge current above 90 kA and the discharge current rise time 4x10 12 A/s, which is sufficient for investigation of amplification in non-traditional electronic transitions.

Compact, battery powered, 400-kV, 40-joule portable Marx generator

Abstract: Summary form only given, as follows. The experimental results of a portable, battery powered, 400-kV, 40-Joule compact Marx generator are presented. The Marx Generator, high voltage power supplies, batteries, and remote fiber optic high voltage enable and trigger control circuits are all contained in an aluminum tube measuring 5 inches in diameter and 20 inches in length. The space within the tube is divided into the Marx Generator section and the power supply section. The Marx Generator section is completely modular and can be easily unplugged to facilitate repair or exchange. The use of non-encapsulated, 22 nF, 10 W surface mount chip capacitors, mounted to a printed circuit board together with the charging resistors, resulted in a very compact assembly. The capacitors and charging resistors are potted in a dielectric gel while the spark gaps are independently insulated with SF/sub 6/ and aligned in a line-of-sight configuration for UV coupling. The entire Marx Generator section is packaged in a Lucite tube, approximately 10 inches in length, which can be pressurized to 50 psi. Rep rates of 1 pps and rise times of 20 ns are typical.

A simple high-voltage pulse generator for laboratory use

Abstract: This paper describes a simple and compact pulse generator designed for the production of short-duration low-energy pulses at up to 500 kV. The circuitry required is much less complicated and expensive than that of a Marx generator of comparable performance and, unlike pulse generators employing exploding fuses or foils, no parts need to be replaced between firings. An experimental unit used extensively for calibration purposes in an ongoing university research programme has performed with great reliability. (4 pages)

Simulation of semiconductor opening switch physics

Abstract: Summary form only given. Semiconductor opening switches (SOS) are able to interrupt currents at density levels of up to 10 kA/cm2 in less than 10 ns. If stacked, SOS diodes can hold off voltage levels above a few 100 kV. They are therefore ideal for the design of compact high voltage pulse generators of the GW-class for industrial applications. The aim of this work was to improve our understanding of the opening process in a semiconductor diode of SOS-type with a doping profile of p+pnn+ structure. To simulate the physical processes inside this diode the code POSEOSS was developed. It contains a detailed physical model of charge carrier transport under the influence of density gradients and electric fields and considers all relevant generation and recombination processes. It possess a large degree of flexibility and allows to carry out parameter studies to determine the influence of different physical quantities, like doping and impurity levels. Applying the code, using realistic values for the charge carrier mobility, it was found that the opening process starts first at the n-n+ boundary, in contradiction to results published by other authors. Based on the simulation results a simplified SOS equivalent circuit model has been developed which can be used in the circuit simulation program PSpice. A new pulse generator scheme based on inductive stores is proposed, in which power multiplication is achieved by unloading the inductors, previously charged in series, in parallel. This scheme can be considered as the inductive equivalent of a Marx generator. We present Pspice simulations of such a scheme based on semiconductor opening switches. The theoretical results were compared to measurements obtained with a simple experimental set-up using two 100 kV SOS-switches. The measurements showed good agreement with the simulation results. Further improvements seem possible by adapting the SOS device structure to the specific generator circuit.

Electron beam, 3.5 MV, 2 kA injector diode diagnostics for the DARHT facility

Abstract: The injector for the second axis of the dual-axis Radiographic Hydrotest Facility (DARHT) is being designed and manufactured in LBNL. The injector consists of a single gap diode, extracting at 2 microseconds, 2 kA (can be extended to 4 kA), up to 3.5 MV electrons from a dispenser cathode. The diode is powered through a high voltage insulating column by a Marx generator. We shall present an overview of the 3.5 MV diode diagnostics, including: the A-K gap voltage measurement using a capacitive voltage divider (dE/dt) probe', cathode (source) current using 12 low inductance stainless steel foil current viewing resistors (CVRs) located on the cathode base plate' and anode dark current collected on the anode shroud using CVRs. A rise in the dark current, can indicate a buildup of an A-K breakdown, and is used to trigger the injector crowbar switch, thus limiting breakdown damage. Beam spillage, generating X-rays around the anode tube and shroud, is monitored using solid state PIN diodes positioned around the anode tube. Furthermore, we shall present the diode diagnostic system conceptual design, development tests, manufacturing and the results of some acceptance tests.

The increase of duration of plasma opening switch conduction phase

Abstract: Summary form only given, as follows. Plasma opening switch (POS) with an applied extrinsic magnetic field allows to Teach maximum voltage multiplication. However, this regime limits the charge density through the POS that reduces current value and pulse duration. The increase of the POS conduction phase duration allows to obtain a substantial growth in charge and energy densities transferred through the POS. This problem is important for the "Baikal" program of superpower generator creation. The machine as assumed will provide a long high current pulse which should be sharpened employing POS technology. To increase the conduction phase time it was proposed to use a special programmable plasma filling of the POS gap. This allows to maintain plasma concentration at low level providing an erosion regime for the conduction phase. The experiments aimed to increase the conduction phase time up to 40 ms used a complex form pulse obtained from a two-stage generator with a POS as a power intensifying element shortened with an inductive load. The first "long" stage utilized a 6 mF and 50 kV battery with a 40 ms current rise time. The second "short" part of the pulse was formed by a Marx generator (0.4 mF, 200 kV) with a quarter of period at 1 ms. The time interval between two parts of the pulse was 20-40 ms.

An ultra-compact Marx HV generator

Abstract: Summary form only given, as follows. This paper discusses the development and testing of an ultracompact, Marx-type, high-voltage generator. This system incorporates high-performance components that are integrated into an extremely compact assembly. Custom, low-profile, annular ceramic capacitors with coplanar extended electrodes provide primary energy storage, and are operated at 60 kV/cm stress levels. Low-inductance, spark gap switches are used for single shot or repetitive operation up to 50 Hz. They incorporate miniature gas cavities imbedded in the central region of the annular capacitors with field stresses along the gas-dielectric interface as high as 130 kV/cm, and thin body sections separating the energy storage capacitors operated at 500 kV/cm. Optimally shaped electrodes and insulator surfaces are used throughout, both to reduce electric field stresses in the triple-point regions, and to spread the fields more evenly throughout the dielectric materials, allowing them to operate closer to their intrinsic breakdown levels. Forward-coupling ceramic capacitors are attached across successive switch-capacitor-switch stages to assist in switching. Specially shaped resistors and inductors are used for charging and isolation during operation. These coupling and charging components withstand 200-kV impulses over their nominal 3-cm length. Pressurized SF/sub 6/ gas is used for electrical insulation in the spark-gap switches and throughout the unit. The pressure housing is constructed entirely of dielectric materials and is made up of segments that interlock with the low-profile switch bodies to provide an integrated support structure for all of the components, permitting operation in any orientation. This ultra-compact Marx generator employs a modular design that can be sized as needed for a particular application. Units have been assembled with 4, 10, and 30 stages and operated at levels up to 100 kV per stage.

Study of breakdown characteristics of solid insulator under different length of high voltage pulses

Abstract: Summary form only given. The breakdown characteristics of solid insulator with two different geometries (a taper insulator and a recessed insulator) are tested under high voltage pulses with two different pulse width (90 ns and 140 ns). The effects of the angle between the solid insulator and the metal electrode and the length of the pulse on the electric field and the breakdown voltage have been investigated both by computation and experiments. The ANSYS code was used to calculate the electric field between the two electrodes and the gas-insulator-electrode triple junctions. The voltage pulse used for testing is produced by a triggered Marx generator capable of 300 kV output with a rise time of 25 nsec and a pulse length of about 320 nsec. The Marx is made up of six capacitors and three gas insulated three-electrode spark gaps arranged in omega-type. In this arrangement, the gaps can trigger in a wide voltage range from 8 kV to 30 kV and the operation was more reliable. Two different length cables used as pulse form line (PFL) to produce different length of pulses. The measurements show good qualitative agreement with the results from computation.

Plasma opening switch with extrinsic magnetic field

Abstract: Summary form only given, as follows. We have demonstrated in series of experiments that plasma opening switch (POS) switching voltage (UPOS) is defined by energy density (w) deposited in the POS plasma. If we then consider a plasma erosion mainly responsible for the effect of POS switching (the erosion effect could be described by Hall or Child-Langmuir models) the energy density (w) could be measured as a function of a system "macro-parameter" such as the initial charging voltage of the capacity storage system (the Marx pulsed voltage generator) UMarx. The POS voltage in this case could be given by UPOS"aw=aUMarx4/7, where a is a constant. This report demonstrates that for the high-impedance POS which has limited charge density transferred through the POS plasma a"2.5 (MV3/7) with no external magnetic field applied. The use of the extrinsic magnetic field allows to increase a up to 3.6 (MV3/7) and to achieve higher voltages at the opening phase - UPOS=3.6UMarx4/7. To verify this approach set of experimental tests has been assigned at RS-20 megavolt-range POS generator. The generator was modified so that the Marx generator could provide output voltage from 160 to 860 kV (with a maximum drive current near 350 kA level). A pulsed magnetic field coil generating the extrinsic magnetic field to enhance POS magnetic insulation has been also introduced. The magnetic field amplitude was near 15 kGs. The maximum POS voltage achieved was 3.5 MV and started from 0.86 MV at the Marx generator.

High-voltage pulse testing of cables on Hawk

Abstract: Summary form only given, as follows. The Hawk facility at NRL was used to pulse test Dielectric Sciences 2158 cables to voltages in excess of 900 kV. The motivation for the testing was to assess the utility of these cables to connect elements in a high-impedance inductive voltage adder system. A high voltage pulse was launched at both ends of a long length of cable to obtain high voltage by wave adding in the middle of the cable while limiting high-voltage complications at the power feeds to the cables. The pulse width was controlled with a point-plane electron-beam diode. The cables tested were approximately 160' long, with a one-way transit time of 240-ns. A pulse with a risetime less than 240-ns launched into both ends of the cable would add to double the voltage in the middle portion of the cable. The cables were connected to the output of one sub-Marx of the Hawk Marx bank, inside the oil tank. A resistive voltage divider was used to monitor the voltage input to the cable, and Rogowski coils to monitor the current input to each cable end. A point-plane electron-beam diode was also connected to the Marx output. The gap closure associated with this diode was used as timed closing switch to terminate the high voltage portion of the pulse. The stored energy of the Marx was dissipated in the damping resistors that were installed between the Marx and the cable, and the cable and the diode. Four lengths of cable were tested. The cable is designed for use as 69 kV AC power cable. Three of the four cables survived pulses in excess of 900 kV before failing, and the fourth cable failed at over 700 kV. Extensive results of the tests on the 2158 cables are presented.

Not Released for Publication The Increase of Duration of Plasma Opening Switch Conduction Phase

Abstract: Plasma Opening Switch (POS) with an applied extrinsic magnetic field allows to reach maximum voltage multiplication [I]. However, this regime limits the charge density through the POS that reduces current value and pulse duration. The increase of the POS conduction phase duration allows to obtain a substantial growth in charge and energy densities transferred through the POS. This problem is important for the "Baikal" program of superpower generator creation. The machine as assumed will provide a long high current pulse which should be sharpened employing POS technology. To increase the conduction phase time it was proposed to use a special programmable plasma filling of the POS gap. This allows to maintain plasma concentration at low level providing an erosion regime for the conduction phase. The experiments aimed to increase the conduction phase time up to 40 ms used a complex form pulse obtained from a two-stage generator with a POS as a power intensifying element shortened with an inductive load. The first "long" stage utilized a 6 mF and 50 kV battery with a 40 ms current rise time. The second "short" part of the pulse was formed by a Marx generator (0.4 mF, 200 kV) with a quarter of period at 1 ms. The time interval between two parts of the pulse was 20-40 ms. References:

E Minor upgrade

Abstract: Summary form only given. The E Minor machine at AWE Aldermaston was originally designed and built as a test-bed for the Marx generator of the 10 MV, 80 ns Mogul E Flash X-Ray machine. For this purpose it had a short (40 ns) oil insulated Blumlein, which originally fed a resistive load. After Mogul E was completed, E Minor was converted into a flash X-Ray machine using an existing, surplus insulator stack from another machine on site (EROS). Unfortunately this insulator stack is only capable of holding off 5.5 MV, well below the maximum possible output of the E-Minor Marx. To continue the X-ray diode development work required for the proposed Hydrodynamics Research Facility (HRF), E Minor needs to upgraded so that it can deliver a 10 MV pulse. During 2001 E Minor will be upgraded to full voltage operation by fitting a Mogul-E-style insulator stack, requiring modifications to the front end of the machine and to the building in which it is housed. Even though the stack is the same as Mogul E, 2D electrostatic modeling software has been used to improve the uniformity of the electric fields along it, compared to Mogul E. This poster will detail the development of the E Minor facility and the modifications required by the upgrade to the building, the machine and the X-ray shielding. Analysis of the insulator stack will also be presented detailing the modifications required to accommodate higher voltage output.

Circuit model for parameter study of Marx generators on megajoule machines

Abstract: Summary form only given, as given. Sandia National Laboratories (SNL) is planning to redesign the pulsed power driver on Z, including the Marx generators, the intermediate-store water capacitors, and the pulse-forming lines to increase the energy delivered to a Z-pinch load. The present Marx system consists of 36 generators that store over 11 MJ of energy. Each generator contains sixty 1.35 microfarad capacitors that are charged in bipolar fashion to 95 kV. The system erects to 5.7 MV when switched, and stores 366 kJ of energy. The 60-capacitors are configured as 12-capacitors to. a row and 5-rows to a generator. A circuit model has been developed using MICROCAP to model one of the 36-Marx generators. The model contains the capacitors, inter-stage switches, switch and capacitor inductances, charging resistors, trigger resistors, and parasitic capacitances between rows. The MICROCAP computed voltage, current, power and energy waveforms will be compared to measured data to validate the model. The model is used to predict the performance of the Marx generator for each design iteration. The paper presents the MICROCAP model of the Marx generator, show the validation results, describe the various design iterations for a new Marx and present the performance results.