Low-Pressure RF Discharge in the Free-Flight Regime

The self-consistent equations system for low-pressure RF discharge in the free-flight regime is formulated. The expressions for the electron energy diffusion coefficient due to electron-neutral collisions and to the electron collisions with the plasma-space charge moving boundary (stochastic heating) are derived. If electron-neutral elastic collisions frequency exceeds the inelastic one, the generalization of conventional two-term approximation for the electron distribution function (EDF) is possible and the space-time-averaged electron kinetic equation can be reduced to the one-dimensional energy diffusion one. The fast electrons escaped to the electrodes can be also accounted for in this equation. It's shown, that in the cases of: (a) spatially uniform ion profile, (b) for frequencies that are small compared with the electron bounce frequency, and (c) for frequencies exceeding the electron plasma one in the sheath, the stochastic heating vanishes.