Electron thermal diffusion instability and standing striations in the plasma of a dc discharge in molecular gases

Abstract

A linear theory of waves in the positive column of dc discharge in molecular gases is presented. Full account is taken of local electron hydrodynamics (s.c. quasi-homogeneous equations), which is derived on the basis of a local non-equilibrium distribution of the electron gas. The production term on the right-hand-side of the ion balance equation gives the familiar ionization wawes, but the ion drift enhanced by the high value of the logitudinal field strength, together with the modification of the pertubed electric field incurred by the electron thermal diffusion, causes the dispersion curve to inersect thek-axis. This provides a natural explanation of the amplified low frequency anode directed wave commonly observed in molecular gas discharges as well as of the standing striation pattern. Numerical examples are given for the case of nitrogen.