Showing papers on "Marx generator published in 1987"

Focused shock spark discharge drill using multiple electrodes

Abstract: A spark discharge focused drill provided with one pulse forming line or a number of pulse forming lines. The pulse forming line is connected to an array of electrodes which would form a spark array. One of the electrodes of each of the array is connected to the high voltage side of the pulse forming line and the other electrodes are at ground potential. When discharged in a liquid, these electrodes produce intense focused shock waves that can pulverize or fracture rock. By delaying the firing of each group of electrodes, the drill can be steered within the earth. Power can be fed to the pulse forming line either downhole or from the surface area. A high voltage source, such as a Marx generator, is suitable for pulse charging the lines.

An Observation of Energetic Electron Beams in Low-Pressure Linear Discharges

Abstract: Experimental observations of energetic axial electron beams in a linear Z pinch operating in the pseudospark mode are presented. The device is driven from a fast Marx generator and allows reproducible production of electron beams over a wide pressure range. Evidence of the importance of electrons generated in the cathode recess in the formation of the beams is presented. An electron beam of high energy which is not associated with formation of the discharge is identified. A second beam of high current density and lower energy associated with gas breakdown is also observed.

High gain, multiatmosphere CO2 laser amplifier

Abstract: A novel TE discharge, 15‐mm aperture, multiatmosphere, CO2 laser amplifier is described, with measured electrical characteristics and gain measurements on the 9.294‐μm, 9R(16) line. The electrical circuit used in this amplifier is a realistic alternative to the Marx bank or conventional LC inversion circuit and, similarly, it would be useful for excitation of other gas lasers as well. This automatically preionized, double‐sided, fourfold LC inversion circuit uses only one spark gap, and it is shown to provide small‐signal gains of 5.7% cm−1, at 120 J l−1 atm−1 and 10 atm. The generalization to an n–stage device, which would be suitable for higher pressures, and larger apertures, is discussed.

Synchronizable, injection‐locked, Q‐switched, mode‐locked, and cavity‐dumped ten‐atmosphere CO2 laser

Abstract: A novel, active, mode‐locking scheme for producing single, line‐tunable, high‐power ultrashort CO2‐laser pulses is described. Using an auxiliary grating‐tuned cw CO2 laser for injection locking on the 9R(16) line, the Q‐switched, mode‐locked, and cavity‐dumped 10‐atm CO2 laser produces single, detection‐limited (<500 ps) pulses of 5‐mJ energy at λ=9.29 μm. Details are given on the traveling‐wave GaAs Pockels cells, both of which are controlled by a single, ultraviolet (UV) triggered spark gap. The time‐locked output pulse is delayed by precisely 300.7 ns with <±50 ps jitter against the UV triggered spark gap, so the laser pulse is synchronizable to an external event to <±250 ps. To drive the transverse‐electric (TE) 10‐atm amplifier section, instead of the conventional Marx bank or inductance‐capacitance (LC) generator, a new type of circuit is used. The automatically preionized, double‐sided LC inversion circuit uses only one spark gap, and a detailed description with operating characteristics is provided.

Fast solid state high voltage pulse generator

Abstract: A fast solid state pulse generator is described which is used to trigger high voltage, high current switches. It consists of a 7-stage marx generator bank switched by avalanche transistors and delivers a negative pulse with a rise time of less than 2 ns and an amplitude of 2.4 kV into a load of 200 ω. The delay between the trigger pulse of TTL level and the output pulse is 16 ns. The jitter is well below 100 ps.

Laser-Triggered Gas Switch Improvements on PBFA-II

Abstract: : PBFA-II is a thirty-six module ion accelerator built by Sandia National Laboratories for inertial confinement fusion feasibility studies [1]. In the water-filled, pulse-forming section of the accelerator, each module is fitted with a 5.0 MV, SF6-filled gas switch located between an intermediate storage capacitor and the first pulse-forming line (Line 1). The intermediate storage capacitor is charged to 4.8- 5.0 MV in approximately 950 ns by a Marx generator located in the oil section of the machine. The gas switch is required to close on command and transfer the stored capacitor energy to Line 1, a coaxial transmission line of 100 ns two-way electrical length. The switches are triggered by a single 3.0 J KrF laser located under the accelerator; a complex beamsplitting/ distribution system is used to deliver simultaneous 20-40 mJ, 35 ns FWHM beamlets to the individual switches.

Investigations into the design of multi-terawatt magnetic switches

Abstract: Magnetic switches were successfully used for pulse compression in the CometII pulsed power module to deliver 2.7 MV and 3.7 TW to a 2 ..cap omega.. matched load. However, the Comet switches suffered interwinding dielectric breakdowns and failed in <100 shots. Initial results from experiments on magnetic switch core insulations indicate that the insulation scheme used in the Comet switches was not optimal and better configurations exist. The Comet magnetic switch failures have been duplicated and studied on the Magnetic Switch Test Module (MSTM), a coaxial, 2 ..cap omega.. PFL driven by a 600 kV Marx generator. The results of these experiments are discussed in detail.

Repetitive mode pulsed ion implanter with magnetically insulated diode

Abstract: A repetitive mode pulsed ion beam apparatus was built using the principle of magnetically insulated vacuum diode driven by a Marx bank. The energy of the individual pulses of 100–300 ns duration at 250 keV maximum voltage is at present below the melting threshold of silicon. Higher doping concentrations were achieved with up to 4000 pulses. We demonstrate the operation by presenting boron and cesium profiles. Good quality metastable TiSi was formed when irradiating Ti layers on silicon with ions from a BN source.

Generation and propagation of high-brightness electron beams from a magnetically crowbarred injector

Abstract: Tests of a 300‐keV electrostatic electron beam injector with a magnetic crowbar switch are described. The saturable ferrite core switch allows generation of a constant voltage, 80‐ns pulse directly from a Marx generator. Inductive isolation in the switch permits direct access to the high‐voltage electrode for thermionic or active plasma cathode experiments. The pulse modulator can drive a 1.5‐kA load. A high brightness 290‐A beam from a felt plasma‐emission cathode was extracted and propagated in vacuum. Because of the reliability of the magnetic crowbar switch, more than 500 shots were accumulated on the cathode at over 1 kA/cm2 with no degradation of the output. The output beam had a normalized brightness of 2.6×108 A/(m rad)2. A solenoidal lens was used to match the space‐charge‐dominated beam into a 1‐m‐long periodic focusing system with 25 reversing solenoidal coils. A beam current of 150 A was successfully transported through the 1.7‐cm radius tube.

Troll: A 4-MV peak voltage pulser

Abstract: A 4 MV peak voltage pulser for the Troll accelerator has been designed, fabricated, and delivered to Sandia National Laboratories by Maxwell Laboratories, Inc The pulser is required to produce a flat-top pulse, with a variable width, to drive a cold-cathode diode The system operates over a range of 2 to 4 MV A 46-stage Marx generator is used to directly drive the diode The diode impedance is relatively high (400 to 4000 cap omega) and causes overshoot of the output voltage due to the stray capacitance of the Marx generator To reduce the overshoot, a unique snubber network was used to damp out the oscillations The pulse width is controlled over a range of 250 ns to 2 mus by a diverter switch The switch is a hybrid two-stage spark gap, with the first gap in trigatron configuration and the second gap self-closed by overvoltage from the first gap

A System for Long Pulse REB Generation

Abstract: A high-voltage pulse generator system producing intense relativistic electron beams (REB)(1.5 µs pulse width, 30 kA peak current, 1 MeV energy) was developed for the use of REB ring formation. This system consists of a Marx generator, 7-m-long transmission lines with plastics-water hybrid insulators and a magnetically insulated transmission line connected with a cathode. Plastics of the hybrid insulators mainly withstand electric breakdown, whereas local electric field concentration is degraded by water having a high permittivity. A high vacuum in the REB formation vessel is realized by the use of an interface of ultrahigh-molecular polyethylene between the line and the vessel. The system has been operated more than twenty thousand shots without encountering a breakdown.

Development of a repetitive 1-MV, 22-kJ Marx generator

Abstract: A 220-kW Marx generator has been designed, built, and tested. It was developed to drive several different pulse power experimental devices requiring repetitive pulses at voltages to 1 MV and energies to 22 kJ per pulse. Experiments are planned that will explore dielectric performance under repetitive stress, cold cathode diode operation, and repetitive switching with saturable inductors at moderate peak power and voltage. A Marx generator was chosen because it has the versatility to drive such a variety of loads. The Marx generator system is made of 16 inductively isolated capacitor stages resistively charged to a maximum of 62.5 kV per capacitor and eight gas dynamic spark gaps. The charging source is a 2-MW dc bipolar power supply. The gas purging system is capable of supplying 3500 SCFH of air at the required pressure. The first two spark gaps of the Marx generator are triggered with a grounded grid thyratron pulser through a 1:10 step-up transformer with an output peaking gap as an (unused) option. At the maximum output (1 MV, 22 kJ) a repetition rate of 10 Hz is possible. This paper will review some of the development work done on rep rated Marx generators as well as explainmore » the present Marx generator configuration and associated hardware systems.« less

A 2.5 Gigawatt Liquid Dielectric Coaxial Pulse Forming Line

Abstract: : The pulse forming line (PFL) can store approximately 600 joules at 100 kilovolts. Line impedance is 0.86 ohm and discharge time into a matched load is 200 nanoseconds. The coaxial line is filled with a mixture of 60% ethylene glycol and 40% water, by weight, yielding the maximum freezing point depression. The dielectric liquid is dearated, deionized and cooled to subzero temperature in order to produce an intrinsic time constant of tens of milliseconds. A 50 kilovolt DC power supply with a current rating of 4 amperes is used to resonantly charge the PFL to 100 kilovolts in the millisecond time regime. A Marx generator is used for fast charging at high voltage. The PFL is being used for investigation of long term charging and breakdown statistics of water/glycol mixtures. It is also used for switch testing. In this paper, the PFL, charging systems, and liquid dielectric conditioning system are described. Experimental results of long term charging and breakdown statistics are also presented.

Diagnosing high-reliability, low-jitter Marx generators

Abstract: We have made photonic measurements to assess the performance of a bipolar Marx generator. Measurements of the switch‐closing sequence were made with a high‐speed multichannel data recorder using fiber optics to monitor the light produced by each switch closure. Experience gained during this research coupled with computer simulations has led to a fundamental understanding of the operation of these multistage devices. As a result of this research, significant improvement in erection time jitter has been realized. Erection time jitter has been measured as low as 2.6 ns for a 3.2‐MV, 16‐stage PBFA‐I Marx generator. Photonic data are presented from this research program, along with a discussion on the use of computer simulations and photonic measurements in designing low‐jitter Marx generators.

Concepts for high gradient, dielectric cavity, induction accelerators

Abstract: Induction accelerator cavities comprising various arrangements of constant impedance transmission lines have been devised to provide a constant acceleration to a short pulsed beam of electrons. In most of the cavity concepts the lines are charged externally from a voltage source such as a Marx generator and switched internally; in others energy is fed from an external bipolar source. Several cavities based on the former concepts have now been fabricated and can be used to accelerate efficiently electron beams with pulse durations of 10–20 ns and currents of 10–100 kA. Acceleration gradients are, however, limited to a few MeV/m for efficient transfer of the energy from the cavity to the beam. Gradients an order of magnitude higher could be obtained by recirculating an undermatched beam several times through the cavities so that only a fraction of the cavity energy is transferred on each pass. Various ways of magnetically bending and confining the beam to achieve this recirculation have been proposed. An attractive alternative in terms of overall weight, however, is to exploit beam propagation in the ion focussed regime. In this scheme the beam is captured by and follows an ion trail formed by ionizing a very low pressure gas with a laser or, for a curved path, with a low energy electron beam. Efforts to demonstrate this recirculating linear induction technology are underway, notably at Sandia National Laboratory.

Pulsed Power for High Power Electron-Beam Pumped Lasers

Abstract: A primary consideration for operation of many high power gas lasers is the generation of a high voltage, large area electron beam. Beam parameters are dictated by laser requirements. Historically the electrical system typically has consisted of a Marx generator with pulse shaping stages or a pulse forming line. In the latter case, one or more high voltage switches (spark gaps) are required. Generally, these systems have been single pulse with cold cathode diodes. For repetitive systems, there is a trend to replace the Marx generator with a pulse transformer. For long pulses and large diode impedances, the pulse shaping elements can be placed in the transformer primary circuit. Otherwise, a PFL and high voltage switch are still required. The trend in pulsed power systems is to attempt to increase the range over which the PFL is not required. For short pulses (10's of nanoseconds), cold cathodes provide a stable impedance for at least hundreds of thousands of shots at rates to several tens of hertz. For longer pulses, where impedance collapse becomes a problem, the shot life of cold cathodes becomes short and the use of hot cathodes may be necessary. In either case, issues of beam current uniformity over large areas (including control of pinching) and mitigation of arc formation must be addressed. This paper will review on-going work relevant to the electrical systems and beam sources. State-of-the-art will be described and a modest attempt will be made to extrapolate current trends.

The Cerenkov free-electron laser

Abstract: : In the Cerenkov free-electron laser experiments, dielectric-loaded quasi-optic resonators were used to couple the electron beam to the electromagnetic field. Three types of electron beam generators were employed: a pulse-transformer-based modulator (which operates in the 50-250 KV range), a Marx generator (which operated in the 500 kv - 1.1 MV range), and a circular RF accelerator (microtron) operating at 5 Mev. The pulse-transformer-based system was used primarily for mm-wavelength experiments. On the fundamental branch (TM01) of a cylindrical shell-loaded guide, operation between 30 and 150 GHz was obtained. A single resonator will typically tune over a 20-30 percent range and the electronic efficiency peaked near the lower end of the tuning curve for a fixed resonator geometry. The magnitude of the efficiency at wavelengths near 3 mm was typically 4-6%. Operation on TM02 at lower efficiency (0.1-1%) was used to extend the operating range above 300 Ghz (350 Ghz typical). However, efficiencies were obtained on occasion. Overall, the moderate-beam-voltage driven C-FEL is a simple, robust source of mm- and near-mm-wavelength radiation. Its principle disadvantage is the requirement for very careful beam focussing since any substantial charging of the dielectric liner will disrupt the beam flow.