Diffusion Cooling of Electrons in Afterglow Plasmas

Abstract

The results of mass‐identified measurements of the decay of positive atomic ion number densities in low‐pressure rare‐gas afterglow plasmas are reported. At high gas pressure, the loss of atomic ions is due to conversion into molecular ions and by ambipolar diffusion to the wall of the container. At low pressures, the loss of atomic ions is only by diffusion to the wall but at a slower rate than that of ambipolar diffusion; this slow loss rate is interpreted as a manifestation of electron diffusion cooling in heavy rare gases. A semi‐quantitative theoretical explanation of diffusion cooling is offered and shown to be in good agreement with the results of measurements of electron decay rates in Ne and Ar afterglows and of ion decay rates in Ne afterglows. Comparison with ion decay measurements in Ar, Kr, and Xe are also given.