Spatial Variations of Plasma Electron Temperature in a Standing Wave at Microwave Frequencies

Abstract

Spatial variations in electron temperature produced in a steady state, room temperature plasma by an electromagnetic standing wave are considered both theoretically and experimentally. The field amplitudes treated are strong enough to raise the electron temperature considerably, but are still too weak to cause inelastic collisions. The electron temperature balance equation for a steady state, spatially varying plasma is derived from a two-term expansion of Boltzmann's equation. In the weakly ionized case, the theoretical equations yield a temperature relaxation distance which determines the spatial dependence of the electron temperature in response to the standing wave. This spatial variation in electron temperature was then measured experimentally in an afterglow plasma, and the observed degree of variation agreed with theoretical predictions.