Abstract
Helium glow discharges in the p = 6-60 mbar pressure rangehave been investigated experimentally and by means of aone-dimensional self-consistent hybrid model. Unlike most of thehybrid models developed previously for noble gas discharges, ourmodel also includes He2+ molecular ions. The electricalparameters of the discharges, recorded in the experiments, as wellas the electron temperature for the different discharge conditions(determined spectroscopically) have been used as input data forthe hybrid model. Our studies show that He2+ ions are presentin the discharge even at 6 mbar with a concentration comparable tothat of He+ ions. Conversion of atomic to molecular ions andthe associative ionization process are identified as main sourcesof molecular ions. At low pressures the He2+ ions areprincipally lost at the electrodes, while at higher pressures therecombination processes become their dominant losses. As the ratesof recombination processes are strongly pressure-dependent, theoptical emission spectrum changes with increasing pressure andshows significant intensity of He2 molecular bands. Thecontribution of He2+ ions to the ion current at the cathodeas well as their contribution to maintenance of the discharge isfound to be around 10%, even at the lowest pressure of 6 mbar,where He2+ formation in most of the discharge models isneglected.
Published Version
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