Spatial distribution of H atom density in high-density, helicon-wave H2 plasmas measured by laser-induced fluorescence

Spatial distributions of H atom density in high-density, helicon-wave H-2 plasmas were measured by (2 + 1)-photon laser-induced fluorescence spectroscopy. In low-power, high-pressure discharges, hill-type distributions, i.e., the H atom density in the plasma column was higher than that in the outside region, were observed. The hill-type density distribution can be explained by known mechanisms of gas-phase reactions, diffusion, and surface loss of H atoms. On the other hand, in high-power, low-pressure discharges, deep dips were observed in the spatial distribution of the H atom density. The dip region corresponded to the location of the plasma column, suggesting significant heating of H atoms.