Ionic Ratio Measurements in Small Bore Helium-Neon D.C. Discharges

Abstract

A system was designed and constructed to experimentally determine the ion species present in a small bore (2 millimeter diameter) helium-neon discharge operated in a bypass configuration. Measurements of the ion species present were made at discharge pressures of 1 to 10 Torr at 1 Torr increments in a 99% helium-1% neon mixture at 2.5 mA, 5 mA, 10 mA and 15 mA. Similar measurements were made in a 95% helium-5% neon mixture and 90% helium-10% neon mixture at pressures from 1 to 3 Torr at similar currents. The experimental observations indicates that the dominant ion species present changes from He+ to Ne+ as the pressure increases. The dramatic change in the ratio of species present implies that besides impact ionization, the production of ions through metastable and ion interactions in the positive column must also be considered.