Effects of Changes in Ionization and Attachment Coefficients on the Dielectric Recovery of High-Current Air Gaps

Abstract

Earlier experiments have indicated that the rate of dielectric recovery of high-pressure, high-current spark channels is closely related to the fall of gas temperature. Recent experimental measurements of dielectric recovery in air at 1 atm following a critically-damped 190-kA spark discharge of 100-μsec duration have been made. By using measurements of gas temperature and Paschen's law, recovery characteristics have been derived on the assumption that the sole mechanism operative in the post spark channel is the reduction in gas density. It is shown in this paper that temporal variations in the values of the Townsend primary (α), secondary (γ) ionization coefficients, and of the attachment coefficient (a) can account for the detailed discrepancies between measured and derived recovery curves. During the early recovery period, an increase in γ due to the removal of adsorbed gas layers by the high-current discharge is thought to account for the reduction in recovery voltage below that derived from gas temperature measurements. It is concluded that, at later times, γ has decreased to a point near its predischarge value; an overall increase in electron attachment due to the formation of impurity products by the high-current discharge causes an increase in recovery voltage beyond that predicted from gas density considerations.