Microwave cavity studies of ionization decay in caesium vapour

Abstract

The microwave cavity technique for measuring electron concentration is considered, an experimental study of the effects of holes in the cavity on the field distribution in the cavity is reported and a method is described which enables the relationship between electron concentration and frequency change to be established empirically. A method for continuously monitoring the frequency changes due to ionization is described, and the effect of electron collisions is treated theoretically. A technique allowing instantaneous measurements of electron concentration and rate of decay of concentration is described.The decay of ionization in afterglows in caesium vapour has been studied, giving recombination coefficients which vary with pressure from about 0·3×10−6 cm3 s−1 at 0·5 torr to about 2×10−6 cm3 s−1 at 3 torr, consistent with a dissociative process. At late stages in afterglows, where diffusion loss dominates, estimates of reduced mobilities of diffusing ions suggest that at 0·1 torr the Cs+ ion dominates, whereas at pressures of about 10 torr the Cs2+ ion is more important. Measurements of electron collision frequency as a function of vapour pressure between 0·1 and 4 torr are reported.