Photocathodes for Compact Optical Triggering of Back-Lighted Thyratrons

Light-activated pseudospark switches, also called back-lighted thyratrons (BLTs), are low pressure (typ. les0.5 Torr), high voltage (typ. 10-50 kV), high current (1-ges100 kA) glow-mode switches. It is of interest to develop ultra-compact BLTs with reliable and practical optical triggering systems for applications of compact pulsed power. The present work investigates the utility of photocathode materials inside mini-BLTs to enhance the switch performance, improve the trigger characteristics (delay, jitter and reliability), and provide optimal conditions for compact optical triggering, including the use of light emitting diodes. Photocathode material properties, including low work function, high quantum yield under the mini-BLT operation pressure (0.1-1 Torr), and sufficiently robust to maintain a reasonable lifetime, are critical in material selection. We present results of investigations of a variety of cathode materials as potential candidates for BLT cathodes. Photoelectron yields of candidate cathode materials are measured in a test bed under relevant vacuum conditions with and without applying positive bias at the collector.