Electric Potential Structure in the Extraction Region of the Negative Hydrogen Ion Source

Abstract

Plasma parameters were compared in the extraction region of a negative hydrogen (H⁻) ion source between the discharge sustained by tungsten (W) and tantalum (Ta) high temperature cathodes. A hydrogen plasma driven by the Ta filament showed lower electron temperature and higher ratio of positive ion saturation current to negative ion/electron saturation current than a plasma excited by the W filament. Plasma potential indicated different spatial distribution along the direction of H⁻ ion extraction corresponding to the voltage biased on the plasma electrode. These results are correlated to the intensities of the H⁻ ion extraction current.