Time lag and recovery time of neutral depopulation in compressed gases in a point-plane discharge

Abstract

The experimental analysis of the variation of the neutral molecule density induced by the first corona in a 2 cm point-plane pulsed discharge in air (2-9.5 bar) and SF6 (560 Torr-2 bar) is performed by a new diffracted schlieren technique (schlieren device associated to a photomultiplier). Two time constants-the time lag and the recovery time-have been measured in the vicinity of the point electrode where the neutral depopulation mechanism first appears and is maximum. The time lag represents the inertia time of the gas to the energy injected, that is to say the time between the energy injection and the beginning of the variation of the neutral density in the core of the discharge. In air for these experimental conditions, the time lag is invariable and equal to 60+or-5 ns. The recovery time is the delay for the neutral-gas density perturbed by the first corona to get back to its initial density. Irrespective of which gas is used, the recovery time is of course a function of the injected energy, but also a strongly decreasing function of the duration of the HV pulse.