Helium glow discharges in the p = 6-60 mbar pressure range have been investigated experimentally and by means of a one-dimensional self-consistent hybrid model. Unlike most of the hybrid models developed previously for noble gas discharges, our model also includes He2+ molecular ions. The electrical parameters of the discharges, recorded in the experiments, as well as the electron temperature for the different discharge conditions (determined spectroscopically) have been used as input data for the hybrid model. Our studies show that He2+ ions are present in the discharge even at 6 mbar with a concentration comparable to that of He+ ions. Conversion of atomic to molecular ions and the associative ionization process are identified as main sources of molecular ions. At low pressures the He2+ ions are principally lost at the electrodes, while at higher pressures the recombination processes become their dominant losses. As the rates of recombination processes are strongly pressure-dependent, the optical emission spectrum changes with increasing pressure and shows significant intensity of He2 molecular bands. The contribution of He2+ ions to the ion current at the cathode as well as their contribution to maintenance of the discharge is found to be around 10%, even at the lowest pressure of 6 mbar, where He2+ formation in most of the discharge models is neglected.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Acoustics and Ultrasonics
- Surfaces, Coatings and Films