NONLOCAL ELECTRON KINETICS IN COLLISIONAL GAS-DISCHARGE PLASMAS

Nonlocal phenomena in electron kinetics of collisional gas discharge p lasmas, their kinetic treatment by a nonlocal approach, and relevant e xperimental results are reviewed in this paper. Using the traditional two-term approximation for the electron distribution function, a gener al method to analyze electron kinetics in nonuniform plasmas in de and RF fields for atomic gases is presented for the nonlocal case, when t he electron energy relaxation length exceeds the characteristic spatia l scale of bounded plasmas. The nonlocal method, which is based on the great difference between the electron mean free path for the momentum transfer and the electron energy relaxation length, considerably simp lifies the solution of the kinetic equation and, in a number of cases, allows one to obtain analytical and semi-analytical solutions. The ma in simplification is achieved for trapped electrons by averaging the B oltzmann equation over space and fast electron motion. Numerous exampl es of spatial nonlocality are considered in the positive column and ne ar the electrodes of de glow discharges, in spatial relaxation of the electron distribution and in striations, and in capacitively and induc tively coupled low-pressure RF discharges. The modeling of fast beam-l ike electrons is based on a continuous-energy-loss approximation with the assumption of forward scattering. Simple analytic expressions for the fast electron spectrum are obtained in cathode regions of de disch arges with planar and hollow cathodes.