Operation of a triggered vacuum flashover switch on pawn

Abstract

Pawn is a prototype inductive storage pulsed power generator with two switching stages. The first stage is a wire fuse array driven by a low voltage (/spl ap/40 kV) capacitor bank, and the second stage is a fast opening vacuum switch such as a plasma erosion opening switch. A triggered vacuum flashover switch isolates the fuse stage from the second stage during fuse conduction. The switch consists of an insulating ring sandwiched between electrodes. Ultraviolet light and plasma from small spark discharges initiate a flashover of the insulator surface to close the switch. The trigger command is sent by fiber optic link. The switch can be command triggered after holding off voltages for /spl ap/15 /spl mu/s; peak holdoff voltage is /spl ap/85 kV. The time to closure decreases from 240 ns at a closing voltage of 15 kV to 140 ns at 50 kv with a typical jitter of /spl plusmn/50 ns. Typical fuse stage output current is /spl ap/1 MA with an average risetime of 1/spl mu/s. Current density in the switch is approximately 25 kA/cm/sup 2/. The risetime of this current pulse can be varied by a factor of two by triggering the switch at different times (closing voltages). Switch design, operation, timing jitter characteristics and multiple shot use will be discussed.