SIMULATION OF THE HIGH-PRESSURE MERCURY DISCHARGE LAMP DURING THE MIDDLE PHASE OF START-UP (MEDIUM MERCURY PRESSURE)

This paper deals with the modelling of the medium pressure Hg and Hg-A r positive column (Hg pressure range 5-350 Torr). The aim of this work is to simulate, in a first approximation, the middle phase of the Hg high-pressure lamp warm-up. In this approach, the main assumption is t hat time evolution of the discharge can be divided into a succession o f stationary sub-phases characterized by the Hg partial pressure. Thus , we present here a self-consistent steady-state collisional-radiative model describing the middle sub-phase. This model includes volume rec ombination of Hg atomic and molecular ions, as well as several atom-at om inelastic scattering mechanisms. Calculations are carried out for b oth pure Hg and Hg-Ar discharges. Our results, which are in good agree ment with experimental data from the literature, confirm that plasma t hermalization occurs in the middle start-up phase (electron and gas te mperatures become equal during this phase). Furthermore, this simulati on shows the importance of different elementary processes, like atom-a tom inelastic scattering, for the medium pressure plasma description. In fact, these mechanisms cannot be neglected until LTE conditions are reached.