Thermal study of a plasma of a highpressure mercury electric discharge

• Published in: The 33rd IEEE International Conference on Plasma Science, 2006. ICOPS 2006. IEEE Conference Record - Abstracts p. 130
• Main Authors: Zissis, Georges, Charrada, Kamel, Araoud, Zouhour
• Format: Conference Proceeding
• Language: English
• Published: IEEE 2006
• Subjects: Electron tubes; Lamps; Phase measurement; Plasma applications; Plasma simulation; Plasma temperature; Thermodynamics
• ISBN: 1424401259; 9781424401253
• ISSN: 0730-9244; 2576-7208
• DOI: 10.1109/PLASMA.2006.1707002

Summary form only given. The simulation of the high pressure mercury lamp during the warm-up phase is a very complex problem because of the numerous and various physical processes that should be taken into account. In fact, it takes several minutes for such a lamp to warm up to its operating conditions (several minutes). During this time, there is a substantial change in the mercury pressure; we deal with a low-pressure mercury-rare gas discharge (~10 -3 torr) at switch-on, to a high-pressure discharge (thousands of torr) in practically pure mercury at operating conditions. Later studies of this transitory phase were carried out in particular by Stambouli et al. while neglecting the effect of the convection. In this work, we propose a 2D model to study the operating phase of a high pressure mercury lamp. This model makes possible to describe the evolution of various thermal quantities during this phase and to measure the effect of the convection on the thermalisation of such discharge. To simplify the problem we divide the warmup time into three time intervals (phases). The first, the `post-ignition' phase, begins immediately after the lamp is turned on. During this phase, the electric field in the discharge changes very slowly with time. The second, the `evaporation phase', is characterized by intense evaporation of mercury. The mercury vapor pressure continues to be the saturated vapor pressure and is determined by the wall temperature of the discharge tube. The third, the `pre-operating' phase, is characterized by close to equilibrium discharge conditions and the rapid rise of the electric field. Our model allows us the calculation of the characteristics of the discharge during the third phase. To describe it, we assume the concept of the local thermodynamic equilibrium (LTE). After the validation of our calculations with the experimental data of Stambouli et al., justifying the suitable choice of the various coefficients and approximations used, this model has been applied particularly to the description of the thermal behaviour of the plasma in such conditions. The results obtained within this framework, show amongst other things, that the losses by conduction in the lamp have almost the same value during the warm-up phase. Those by convection remain weak and increase in the course of time without reaching the value of the losses by conduction