Mechanism for anomalously high voltages in high-pressure dc microdischarge mixtures of He, Ne, and Xe

Abstract

Electrical characteristics in the microdischarge experiments of Postel and Cappelli [J. Appl. Phys. 89, 4719 (2001)], show that voltages are higher in mixtures of helium and xenon than in pure xenon in the abnormal glow discharge regime. While originally attributed to the possible formation of heterodimer ions which have lower secondary emission coefficients, we show here that we can reproduce the general trends seen experimentally with a one-dimensional fluid model by taking into account the charge exchange process, He++Xe→He+Xe+. The reaction rate coefficient used (10−9 cm3 s−1) corresponds to that for ions with energy of around 1 eV, which is not an uncommon energy for ions in the cathode sheath of strongly collisional microdischarges. Experimental results are also presented for mixtures of He, Xe, and Ne, at 50 Torr and 250 Torr.