Numerical simulation of dc high-pressure discharge lamps including electrodes

The subject of this paper is a novel modelling method for dc operated high-pressure discharge lamps including both electrodes. No subdivisions of the discharge space into different regions (e.g. space charge layer, ionization zone, plasma column) is necessary. Starting from general diffusion equations, this goal is achieved by using a differential equation for a non-LTE electrical conductivity which is applicable for local thermal equilibrium (LTE) regions as well as non-LTE plasma regions close to electrodes. This novel approach is valid only for high-pressure conditions, where the product of electron mean free path and electric field is such that the mean energy gain of electrons is considerably less than the ionization energy of the discharge gas, so that the same local kinetic energy distribution can be assumed for the electron, the ion, and the neutral gas components anywhere within the discharge. Boundary conditions for this non-LTE electrical conductivity at cathode and anode are derived. We present modelling results for Hg- and Xe-discharge lamps ( p ⩾1 MPa). Comparison with results from traditional models using plasma layers will be presented and discussed. Convective flow within the lamp is not included yet, as the emphasis of this paper is on the regions close to anode and cathode.