High Speed Pulse Breakdown of Pressurised Uniform Gaps

Abstract

Mr. Laird Bradley (1) has performed some nice experiments on pressurised nitrogen gaps, measuring their breakdown voltage for fast rising pulses. The results show breakdown fields considerably above the uniform field DC values. For instance, for a gap of 1/2 cm at 2 atmospheres pressure, the breakdown field is some 6 times the DC value. His note shows that this behaviour can be accounted for by assuming that a streamer transit phase occurs after a rather rapid Townsend avalanche phase and that the streamer time predominates over the latter. He fits a relation of the form Fd¹/⁶t¹/⁶ = ℓ to the data and derives the pressure dependency of ℓ. The values of ℓ fitting the experiments are some 3 times that applying to point plane data. The aim of this note is to estimate these values using the point plane streamer data and while it is to be expected that the fit to the data obtained will only be rather approximate, it may then be used to deduce trends.

24 August 1970 SSWA/JCM/708/107