Effects of plasma-density inhomogeneity and collisions and theirrelation to maintenance of waveguide discharges by Trivelpiece-Gouldmodes: II. Numerical analysis

Abstract

The effects of collisions and radial inhomogeneity of the plasmadensity on the behaviour of the azimuthally-symmetric Trivelpiece-Gouldmodes (including the waveguide resonance and the wave resonance absorptionat the upper hybrid frequency) are treated in this study in terms of theirrelation to gas-discharge production in an external magnetic field.Numerical solutions for the wave-field patterns and for the propagationproperties of the waves are presented and their changes are discussed witha varying averaged plasma density, for various plasma-density profiles.First modifications due to collisions in homogeneous plasmas are presentedfor different values of the external magnetic field. Then, for a givenmagnetic field, the combined effects of collisions and Bessel-type radialprofiles of the plasma density are emphasized. After which, for a givenprofile, the influence is discussed of varying the magnetic field. Itbecame evident that, for low collision frequencies and a cyclotronfrequency less than the wave frequency, the plasma-density profile shapehas a strong impact on the results and that the wave properties, as theaverage density is varied for dominantly diffusive charged particle losses,are badly represented by wave properties in uniform plasmas. The behaviourdiscussed here should be useful in understanding the structure ofdiffusion-controlled discharges maintained in the fields of propagatingTrivelpiece-Gould modes.