Experimental and numerical study of a low-pressure Hg-Ar discharge at high current densities

Experimental measurements of Hg excited state densities and the positive column electric field have been made in a highly-loaded low-pressure Hg-Ar discharge for current densities ranging from 0.05 to 0.6 A cm(-2) and Hg vapour pressures from 1.2 to 13.2 mTorr. Resonance level (Hg 6s6p (3)P(1), (1)P(1)) and metastable level (Hg 6s6p (3)P(0), (3)P(2)) column densities across the positive column have been obtained using white light absorption spectroscopy. The experimental results are compared with numerical predictions from two existing and independent codes. Several physical mechanisms, which are not generally included in numerical models of the Hg-Ar positive column, are suggested as possible causes of the observed discrepancies.