Model of the cathode region and gas temperature of a dc glow discharge at high current density

A model is reported of the cathode region of a de glow discharge at high current density. The distributions of most important plasma species (such as fast electrons, fast neutrals and ions, and energetic sputtered metal atoms) are determined either analytically or using simple semi-analytic methods, taking into account possible strong gas-density/temperature gradients. A heat-transfer equation is used to calculate the gas temperature, and the power-deposition profiles due to fast neutrals and energetic metal atoms are determined at the kinetic level. For the conditions of interest, the power-deposition profiles are shown to be strongly non-local and the assumption of Joule (local) heating to be generally inappropriate. Fast neutrals reflected from the cathode, as well as fast recoil neutrals, are shown to play a key role in determining the rate and spatial distribution of gas heating. Spectroscopic measurements of the gas temperature in a hollow-cathode discharge are carried out over a wide range of discharge conditions. The experimental and predicted gas temperatures are compared and acceptable agreement is found. A strong sensitivity of the model predictions to the assumed particle-surface interaction data is observed. The model can be readily adapted to other types of glow discharge and other geometries. It is computationally efficient and can be useful for fast self-consistent modelling of glow-discharge plasmas.