Space-Charge-Controlled Diffusion in an Afterglow

Calculations of space-charge-controlled diffusion of electrons and positive ions in an isothermal afterglow are presented. In particular, the transition from electron-ion ambipolar diffusion to free diffusion of the electrons and ions is investigated. The results are in qualitative agreement with the experiment of Gerber, Gusinow, and Gerardo insofar as predicting the general features of the transition from electron-ion ambipolar diffusion to free diffusion. In addition, the results substantiate the general behavior implicitly predicted by the more elaborate steady-state calculations of Allis and Rose.