An Exact Theory for the Transient Behavior of Electron Swarm Parameters

Abstract

We have developed (Drallos and Wadehra, 1988; 1989) a simple, yet exact numerical technique for obtaining time-dependent electron velocity distribution functions (EVDF) from which the transient behavior of various electron swarm parameters can be obtained. Our calculations predict overshoots in the electron drift velocity when the initial average energy of the electron swarm is near or below the final equilibrium average energy of the swarm. Less dramatic overshoots (and undershoots) of the ionization rate and the average energy have also been observed in the calculations when the above conditions were present. Recent experimentally observed (Duffy and Ingold, 1988; Verdeyen et al., 1988) current overshoots in Ar-Hg and Ne-Hg discharges and ionization rate overshoots in N₂discharges are presumably related to the initial conditions of the electron velocity distribution function. Analysis of the swarm data has shown that, for a given E/N, the time dependence of various swarm parameters can be accurately fitted by a sum of two exponential terms. For a given gas (Ar or Ne, in our case), the decay constants in the exponentials appear to depend only on the value of E/N.

The support of the Air Force Office of Scientific Research through Grant Number AF0SR-87-03042 is gratefully acknowledged.