New Development of Cesium-Free Negative Ion Sources Based on Plasma-Assisted Catalytic Ionization Method

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Production mechanism of negative hydrogen ions in a plasma-assisted catalytic ionization method is investigated in connection with research and development of cesium-free negative ion source for neutral particle beam injection heating. When positive ions produced by discharge are irradiated onto a metal surface and some of them pass through the metal aperture, negative ions are produced from the back of the irradiation plane. The irradiated metal is used a porous nickel, metal grids made of some elements, or a plasma grid made of aluminum with single aperture. The dominant process of negative-ion production is found not to be desorption ionization owing to collision of fast positive ions with adsorbed hydrogen atoms but neutralization and negative ionization of slow positive ions on the metal surface.