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The negative hydrogen ion current and the electron current extracted from arc discharge negative ion sources exhibit different characteristics when the discharge filament material or the plasma electrode material is changed. The knowledge of these characteristics is of importance for the proper design of an efficient H − ion source. We investigated the effect due to tungsten (W) and tantalum (Ta) adsorption on a stainless-steel plasma electrode and compared the results with the performance of the plasma electrodes covered by Ta and Ti foils. The result showed that freshly deposited Ta enhanced the H − ion current and reduced the co-extracted electron current in the same way as a caesium adsorbed film.

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.

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