Dynamics of the low pressure negative glow

Abstract

Summary form only given. In low pressure Ar-Hg discharges, the cathode thermionic hot-spot is heated primarily by Hg-ion impact. Recent work (Garner and Li, 1997) has resulted in a combined cathode/negative glow model which predicts (among other things) the Hg-ion energy flux incident on the hot spot and the resulting hot-spot temperature. The model requires input data on: electron and ion temperatures, Ar and Hg densities, discharge current, lamp diameter, thermionic work function and hot spot size. However, since only steady state fluid equations are used in the model, the model fails if discharge current and voltage change too fast. This paper will explore the temporal response of the negative glow-hot-spot system to sudden changes in discharge voltage and current. Time resolved observations of the negative glow and cathode hot-spot have been performed. After equilibrium conditions were established, a fast risetime voltage pulse was applied across a few Torr, Ar-Hg discharge. The resulting discharge current pulse was recorded as were the 398.4 nm Hg-ion line emission from the negative glow, the IR radiation from the thermionic hot-spot and the cathode-plus-anode fall voltage (inferred from a movable anode technique).