Space Charge Effects in the Townsend?Huxley Swarm Technique

Abstract

An analytical treatment of space charge effects in the Townsend-Huxley swarm technique is given. The general case of a mixed swarm of equally charged ions and electrons drifting through a gas in which attachment is possible is considered. The case of a pure electron or pure ion swarm is treated as a particular case of the general one. The main result is an expression for R(r,z), this being the ratio of the current collected by a disk of radius r, in the plane z = z, to the total swarm current. This ratio is determined as an explicit function of DIp-, the total current, the electron (or ion) current, and the attachment coefficient. It is shown that space charge effects can be of importance for large currents, low E Ip, and low gas temperatures. Moreover, in practice such effects are only likely to be of interest in thermal swarms.