Longitudinal structure of capacitative radiofrequency gamma discharge and its analogy with a direct current glow discharge

Abstract

The longitudinal structure of a gamma -type RF discharge is computed and shown to have much in common with the structure of a direct current glow discharge. In a sufficiently long gap or at rather high pressures, there are regions of cathode fall, negative glow and Faraday dark space near each of the electrodes. A uniform positive column exists between the electrodes. This pattern is obtained when taking into account non-local effects of the electron spectrum and abandoning Townsend's coefficient to describe the ionization, electron diffusion and electron losses as functions of a local field. The reverse field regions obtained numerically agree with experimental values. It is shown that very low magnitude of the field amplitude and mean electron energy in the plasma are not intrinsic properties of the gamma discharge. The low magnitudes are typical only for sufficiently short gaps and low pressures when the plasma is concentrated in the negative glow region and the Faraday dark space and there is no room for the positive column to form. In long gaps and for high pressure the positive column is formed where the field and electron temperature are as high as in an alpha discharge or in the positive column of a glow discharge.