Computer modelling of the hollow cathode plasma used for nitriding process

A hollow cathode discharge used for ion nitriding of metallic surfaces was studied in terms of fluid modeling. The setup consists of powered anode, grounded cathode and a grid screen placed at a short distance from the cathode. The discharge operated in argon at a pressure of 100 to 400 Pa. The fluid model includes the continuity equations for mean electron, argon atoms and ions densities, and using drift-diffusion approximation for their fluxes. The transport and collision rate coefficients of the electrons are determined as functions of the mean energy by solving the Boltzmann equation. The mean electron energy was determined by solving the electron energy balance equation. In order to obtain a self-consistent electric field, these equations was coupled with the Poisson equation and an equation describing the external circuit. The model yields the current-voltage characteristic of the discharge. Especially, the spatial profiles of the electric potential, the densities of all species, the mean electron energy and collision rates are investigated in relation to discharge current.