Magnesium-Based Photocathodes for Back-Lighted Thyratrons

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. For applications such as these, advances that improve and simplify triggering are important. Here, magnesium was investigated as a photocathode candidate for optically triggered pseudospark switches, also called back-lighted thyratrons (BLTs). A Mg foil on the back surface of a copper BLT cathode reduced trigger delay and jitter by one order of magnitude when a 5 ns, 3 mJ light pulse at 266-nm wavelength was incident at the back of the cathode at a constant switch voltage of 4.1 kV. Delays less than 150 ns were obtained. An increased photoemission due to the lower work function of magnesium is considered as the main reason for the improvement in trigger delay and jitter for the BLT system. Mg-based cathodes are promising for development of compact optical triggering units with low optical energy sources for BLTs.