Design and Optimization of a Low-Impedance Pulsed-Power Marx Generator to Drive High-Power Relativistic X-Band Magnetron

Abstract

One class of high-current relativistic HPM devices, the relativistic magnetron [1], provides a low-impedance (10-50 Omega) load that inherently needs matching to a low-impedance pulsed-power (Gigawatt or greater) supply to operate with maximum efficiency. One of the most common and reliable pulsed-power drivers used to accomplish this is a Marx generator. The University of New Mexico previously used a modified Pulseradreg 110A electron beam accelerator [2] to produce high-power microwaves [3] from a backward wave oscillator (BWO), which was a high-impedance load (130 Omega). This driver will be used for planned experiments with an X-band relativistic magnetron. The main part of the Pulserad's assembly is a Marx generator composed of capacitors, spark gaps and resistors electrically arranged in an 11-stage Marx circuit. The output impedance of the Marx generator is about ~35 Omega (which is why a shunt resistor was required to facilitate operation with the BWO), maximum charging voltage of each single stage is <100 kV, and total stored energy is about 600 Joules. In the present paper some results of the design and optimization efforts aimed at reducing the intrinsic impedance of the Marx generator are discussed. It turns out, for example, that by re-arranging the Marx's electrical circuit from the presently configured 11-stage Marx into a series-parallel connection of 12 capacitors, it is possible to decrease the impedance of the Marx generator down to ~15 Omega (implementing series-parallel connection of 2 parallel lines with 6 series capacitors in each line - 2times6 circuit), or even down to ~10 Omega (implementing series-parallel connection of 3 parallel lines of 4 series capacitors -3times4 circuit). Another feature that will be integrated in the redesign of the Pulseradreg 110 A electron beam accelerator is the use of a brazed ceramic insulator stack to facilitate high-vacuum operation. Successful completion of this upgrade will allow for experimental studies of a low-impedance relativistic X-band magnetron to begin to operate au naturel.