Evidence for molecular-assisted recombination of He+ from particle balance measurements in helium-hydrogen mixture plasmas in PISCES-A

Abstract

Particle balance measurements of He+ ions in He∕H mixture plasma are performed by using wall probes, plunging probes, and spectroscopy. The measurements indicate that radial loss to the chamber wall is the dominant ion sink; nevertheless, a missing ion sink is observed as the plasma hydrogen fraction is increased. This sink term is attributed to hydrogen-mediated recombination of He+ ions, so-called molecular-assisted recombination (MAR). Independent evidence for MAR (acting on hydrogen ions, however) is seen in anomalously large Hα∕Hγ ratios at the cold plasma edge.