Optically triggered pseudospark switches with metal photocathodes

Pseudospark switches have been successfully employed in a variety of pulsed power applications including high power electron beam sources, high power microwaves, and transient plasma ignition for pulsed detonation engines [1-3]. Investigation of magnesium, copper and molybdenum photocathode candidates for optically triggered pseudospark switches, also called back-lighted thyratrons (BLTs), has shown that magnesium has a higher quantum efficiency (up to 1.5×10^-5) under BLT-relevant pressure conditions, compared to copper or molybdenum [4]. Magnesium, copper and molybdenum-based BLT cathodes were experimentally studied. A compact UV laser with an intensity of 3 mJ, and optical power density of 8.5×10⁶ W/cm² per pulse was used as the optical triggering source for these studies. It was demonstrated that both the delay and the jitter of the switch were shortened more than an order of magnitude when the Mg foil was present at the cathode. The electron emission mechanisms contributing to this improvement in delay and jitter for the BLT system are discussed.