Modeling and measurements of tungsten sputtering in high intensity discharge lamps during starting

Summary form only given. We present new results on tungsten linewidths to calibrate absorption data and new modeling results to estimate tungsten flux to the wall. Tungsten linewidths were measured using a two-meter spectrometer in second order. Lamps contained mixtures of Ar and Hg to simulate starting conditions in metal halide lamps. Measured linewidths on the 287.94 nm tungsten resonance transition were on the order of 0.25 cm/sup -1/ during the glow to arc transition, increasing to about 0.45 cm/sup -1/ during the initial thermionic phase. Neutral and ionic tungsten fluxes to the wall were then estimated from absorption and linewidth data as a function of starting current. Calculations were performed using a 1-D numerical model that incorporated both neutral particle and tungsten ion transport. The numerical results revealed a strong dependence of tungsten ion fluxes with Hg pressure during starting. Unusual features in the measured lineshapes will also be discussed.