Performance of tantalum as plasma electrode material in negative hydrogen ion sources

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.