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An ultra-compact Back-Lighted Thyratron (BLT) holds the promise in high voltage (above 30 kV), high current (peak current 10 kA) switching at high repetition rates (1 kHz) in a small volume (100 cm3 or less). A helium-filled mini-BLT with the effective electrode volume of 15 cm3 was demonstrated to hold off 40 kV. Novel approaches enabling compact and affordable optical triggering are essential for the development of ultracompact BLTs. Photocathodes with relatively high quantum efficiencies while still sufficiently robust to survive in a BLT-relevant discharge environment were investigated. Mg was identified to be the most promising metal photocathode material compared to Cu and Mo. Besides the Schottky effect, secondary electron emission due to the formed MgO layer at the surface of the Mg foil was considered to play an important role in the photon-induced discharge initiation process, which results in improved triggering characteristics for Mg photocathodes. In addition, compact optical triggering sources based on intense ultraviolet light emitting diodes (UV LEDs) were assembled for BLT triggering. Although the current version of the light source based on a single UV LED failed to trigger the BLT, approaches combining intense UV LED lamps and novel photocathodes with higher quantum yields would result in compact optical triggering for ultra-compact BLTs.

In this paper we present our work on breakdown studies conducted in helium at partial vacuum conditions for a point-to-point electrode setup. A high frequency pulsed voltage signal is applied across the electrodes and the voltage-current characteristics are observed. The applied signal consists of a train of square pulses in the frequency range of 50 to 200 kHz with 50% duty cycle and rise/fall times in the range of 20-30 ns. These studies were conducted to understand and compare the role of the pulse repetition rate in electrical breakdown initiation in low pressure conditions. Preliminary data of voltage and current waveforms, along with the light emission data are presented. The optical data collected by a PMT (Photo Multiplier Tube) as a function of the time is presented in comparison to the varying voltage., Published in the Proceedings of the 2006 International Conference on Power Modular (27th), held in Arlington, VA on 14-18 May 2006, p112-115.