Negative ion densities in high-density, low-temperature recombining hydrogen plasmas

Abstract

The objective of this work is to investigate the density of negative hydrogen ions in high-density, low-temperature recombining hydrogen plasmas. The recombining hydrogen plasmas were obtained in a compact divertor simulator excited by helicon-wave discharges. The electron density and the electron temperature of the recombining plasmas were (1–4) × 1012 cm−3 and 0.1–0.2 eV, respectively, which were evaluated by comparing the population distribution of the excited states of atomic hydrogen with the Saha–Boltzmann equation. The ratio of the negative ion to electron density ranged between 0 and 0.02 in the recombining plasmas, which was one order of magnitude lower than that observed in a plasma with an electron density on the order of 1011 cm−3. The less efficient production of negative hydrogen ions may be attributed to significant dissociation of molecular hydrogen in high-density plasmas.