Experimental and theoretical study of the warm-up of a high-pressure mercury discharge close to steady state

Summary form only given. The warm-up phase of a pure mercury high-pressure discharge is investigated. Understanding the properties of plasmas during their transitory phase is a key technological challenge in the lighting industry sectors. The simulation of the warm-up phase is also of scientific interest since it reflects the influence of the pressure variation on various elementary processes occurring in the discharge. A quartz vessel with 13.5 mm inner diameter and 34 mm electrode distance is filled with 21 mg Hg and 60 mbar Ar as start gas. The discharge is driven at a nominal power of 245 W with a current source providing a 120 Hz square wave signal. A consistent set of experimental data is acquired during the warm-up phase of the lamp like current, voltage, wall temperature, side-on spectral radiance and spectral radiant flux. Due to quasi dc operation at constant current the experiment is highly suitable for theoretical simulations and allows for comparison with former investigations. A time-dependent two-dimensional computational fluid model has been adopted to investigate the dynamic behavior of the high-pressure mercury lamp during the last phase of the warm-up period. The model solves the combined momentum, continuity, energy, and electric field equations for the plasma and the energy equation for the wall. Hence, the main purpose of the present paper is to validate this model, which enables us to analyze the dynamic convection as the mercury pressure increases, by experimental results. First results show that the temporal evolution of wall temperature and discharge voltage can be reproduced by the model calculations. Stationary conditions are achieved after ca. 160 s reaching wall temperatures around 1000 K and a discharge voltage of around 110 V.