Diffusion in a Slightly Ionized Gas with Application to Effusion from a Shock Tube

A sampling technique for measuring the diffusive flux of charged particles from an ionized gas to a cold wall by measuring the effusive electrical current through a small orifice in the wall has been used to study slightly ionized argon behind reflected shock waves. The technique is described and the transient diffusion process upon which it depends is considered in some detail. Computations based on a simple one-dimensional isothermal charge diffusion model illustrate the features and give the result that the effect of the electric body forces is generally greater on the ions and less on the electrons than originally expected. These results are used in an approximation to the nonisothermal problem to give a relation between the measured effusive current and the ion density in the hot gas. Preliminary observations of the dependence of ion density on time and temperature in the initial stages of ionization relaxation are reported. Simple considerations of the chemical kinetics indicate that for the portion of the process observed (degree of ionization about 10−5 times the equilibrium value) the ionization of argon results from a complicated series of consecutive reactions.