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

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) x 10(12) 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 10(11) cm(-3). The less efficient production of negative hydrogen ions may be attributed to significant dissociation of molecular hydrogen in high-density plasmas.