Characteristics of pseudospark switches for pulsed power modulators

Abstract

Pseudospark switches (PSS) are considered to be an alternative not only to thyratrons or medium-power spark gaps but also to ignitrons. A lifetime of more than 10/sup 8/ discharges with a corresponding total charge transfer of 600 kC was achieved in laser circuits. Electrode erosion is still the main limiting factor to make high power PSS a serious competitor to commercially available switches. One approach to solve this problem is to distribute the total current on several discharge channels with a common hollow cathode. The other one is to look for suitable electrode materials or compounds of them. In order to distribute the discharge homogeneously over more than one single channel synchronous triggering of all channels is indispensable. The trigger method used is a pulsed glow discharge. The characteristics of the trigger discharge as a function of delay and jitter was investigated in combination with actual triggering of all channels. After successful triggering of all channels the corresponding current filaments try to pinch by self-magnetic fields. For long current pulses (i.e. more than 1 or 2 /spl mu/s for a 80 kA peak current) a single plasma column develops in the symmetry axis of the device. Streak photographs allow determination of pinch time as a function of the peak current, the number of channels, the gap distance and so on. A better understanding of electrode phenomena is essential in order to improve PSSs to carry high peak currents and simultaneously allow high charge transfer. The critical current density at which electrode erosion dramatically rises is still an unknown parameter.