Influence of filament materials on vacuum ultraviolet emission in H− ion source

The increase of H− current is observed, when the tantalum filaments are used instead of the tungsten filaments. In terms of the production rate of vibrational populations of hydrogen molecules with tungsten and tantalum filaments, we measured the Werner and Lyman emission bands (90–170 nm) the vacuum ultraviolet region to obtain the spectra of molecular hydrogen in an ion source, and observed a significant difference of spectrum between the two cases. From the pressure dependence, it is found that the production rate of vibrationally excited hydrogen molecules is well correlated with the H− density measured by photodetachment in hydrogen plasmas.