Spatiotemporal relaxation of electrons in non-isothermal plasmas

A powerful method for the study of time-dependent electron kinetics in spatially one-dimensional plasmas is presented. The method is based on the solution of the space- and time-dependent kinetic equation for the electron velocity distribution function in two-term approximation. The resulting three-dimensional partial differential equation for the isotropic part of the velocity distribution function is numerically solved as an initial-boundary value problem over the space of the spatial coordinate and the total energy proceeding in time. As an application, the spatiotemporal relaxation of electrons in the column-anode plasma of a glow discharge in krypton, acted upon by a space-independent electric field and initiated by a constant electron influx at the cathode side of the plasma, is studied. The electron relaxation process is traced up to the establishment into a spatially structured, time-independent state. A detailed analysis of the spatiotemporal behaviour of the velocity distribution function and relevant macroscopic quantities of the electrons is given for different electric field strengths and boundary conditions. In particular, a significant increase in the relaxation time of the spatiotemporal electron relaxation compared with the relaxation time to approach steady state in spatially homogeneous plasmas has been found.