Prebreakdown phenomena in cryogenic liquids

Streamer initiation and propagation processes were observed in liquid nitrogen under non-uniform field. A high magnification (63.5/spl times/), high speed (up to 50 ns/Frame) shadowgraph system was employed for the optical measurements. Under impulse voltage conditions, there were two types of negative streamer; one was a slow (10/spl sim/100 m/s) bush-like streamer and the other a filamentary one which was faster (100/spl sim/500 m/s) and grew straight or sometimes winding towards the opposite electrode. In both cases, the initial structure of the streamer appeared to be a filament. In conjunction with the optical study, current pulses were also measured simultaneously using a LED current pulse measurement system. The onset of the current pulse occurred prior to the streamer inception for both types of streamers but their frequency and amplitude were quite different.<>