Marx generator

About: Marx generator is a research topic. Over the lifetime, 1276 publications have been published within this topic receiving 8970 citations.

Precise Laser Initiated Closure of Multimegavolt Spark Gaps

Abstract: Single‐ and double‐channel laser triggered switches in high pressure gas have been designed and operated in the voltage range from 1 to more than 3 MV. Jitter times of <1 to 3 nsec were observed in most cases. Gas pressures of 10.5 and 21 kg·cm−2 were used. The gases were either 100% nitrogen or various mixtures of N2, SF6, and Ar. Significant accomplishments were (1) the simultaneous firing of four stages of a Marx generator by an optically divided laser beam, (2) up to 40% reduction in the risetime observed in the output pulse from a multimegavolt dc generator when switched into a load through two simultaneously laser triggered channels, and (3) the design and operation of a laser triggered, dc charged switch at more than 3 MV with subnanosecond jitter.

A Compact, Low Jitter, 1 kHz Pulse Repetition Rate Gas-Switched Pulse Generator System

Abstract: We present the results of an experimental research effort focused on developing a compact, low jitter, command triggered, high peak power, high pulse repetition rate (PRR), gas-switched pulse generator system. The pulse generator is command triggered by a single TTL level pulse generated by a control system implemented using software and a computer interface card. The TTL trigger pulse fires a solid-state trigger pulser that closes the first stage switch in a modular Marx-like pulse generator. The control system also sets the charge voltage of a 2500 J/s high voltage capacitor charging power supply and inhibits capacitor charging during firing of the pulse generator. The individual Marx stages are compact and stackable and utilize surface mount multilayer ceramic chip capacitors and field enhanced spark gap switches. The stage capacitors are charged in parallel through mutually coupled inductors in series with resistors. This charging scheme allows for high PRR operation limited only by the stage switch recovery time and the power of the capacitor charging power supply. The stage switches are optically coupled to aid in Marx erection and to minimize system jitter. The Marx generator is housed in a pressure vessel and operated in a low pressure dry air environment. The design exhibits a low inductance which is estimated to be <20 nH based on the measured output voltage rise time and load resistance. The pulse generator system has been operated in a burst mode at a PRR in excess of 1 kHz with good output voltage regulation. The jitter of the Marx generator, characterized independent of the trigger pulse, was measured and found to be ~500 ps.

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.

Methods for characterizing x-ray detectors for use at the National Ignition Facility.

Abstract: Gated and streaked x-ray detectors generally require corrections in order to counteract instrumental effects in the data. The method of correcting for gain variations in gated cameras fielded at National Ignition Facility (NIF) is described. Four techniques for characterizing the gated x-ray detectors are described. The current principal method of characterizing x-ray instruments is the production of controlled x-ray emission by laser-generated plasmas as a dedicated shot at the NIF. A recently commissioned pulsed x-ray source has the potential to replace the other characterization systems. This x-ray source features a pulsed power source consisting of a Marx generator, capacitor bank that is charged in series and discharged in parallel, producing up to 300 kV. The pulsed x-ray source initially suffered from a large jitter (∼60 ns), but the recent addition of a pulsed laser to trigger the spark gap has reduced the jitter to ∼5 ns. Initial results show that this tool is a promising alternative to the other flat fielding techniques.

Use of a radial self-field diode geometry for intense pulsed ion beam generation at 6 MeV on Hermes III

Abstract: We investigate the generation of intense pulsed focused ion beams at the 6 MeV level using an inductive voltage adder (IVA) pulsed-power generator, which employs a magnetically insulated transmission line (MITL). Such IVA machines typical run at an impedance of few tens of Ohms. Previous successful intense ion beam generation experiments have often featured an “axial” pinch-reflex ion diode (i.e., with an axial anode-cathode gap) and operated on a conventional Marx generator/water line driver with an impedance of a few Ohms and no need for an MITL. The goals of these experiments are to develop a pinch-reflex ion diode geometry that has an impedance to efficiently match to an IVA, produces a reasonably high ion current fraction, captures the vacuum electron current flowing forward in the MITL, and focuses the resulting ion beam to small spot size. A new “radial” pinch-reflex ion diode (i.e., with a radial anode-cathode gap) is found to best demonstrate these properties. Operation in both positive and negat...