Starting mechanisms for high pressure metal halide lamps

Summary form only given. High pressure metal halide lamps typically have cold fills of a rare gas (usually Ar) of 10 Torr. Starting of the lamp involves applying a high voltage pulse to the electrodes, breaking down the gas, and upon heating produces a thermal arc. Lamps often include auxiliary electrodes to produce preionization, either by electron impact or by photoionization. To investigate these processes, a 2-dimensional lamp model has been developed. The model uses a conformal triangle-based mesh to resolve fine structures. Charged particle transport is based on a drift-diffusion formalism with Sharfetter-Gummel fluxes, solved implicitly coincident with Poisson´s equation using a modified Newton´s method. Neutral particle transport is separately implicitly solved using the method of successive -over-relaxation. Electron transport coefficients are obtained from either a local-field approximation or by solving the electron energy equation. Plasma properties during startup will be discussed for a selection of electrode geometries, voltage formats and impurity concentrations.