Characteristics of extracted ion beam from a cesium-free negative ion source using sheet plasma

Abstract

We report the characteristics of extracted beam current in the test plasma produced by direct current for sheet plasma upgrade producing negative ions by volume production without cesium (Cs) seeding. The negative hydrogen ion beam is extracted by a two-grid extraction system, which is located at the periphery of the sheet plasma. Experimental observations show that (i) negative hydrogen ions are successfully extracted from the sheet plasma by single/multi-aperture grids and (ii) the ratio of the extracted electron current IEG(e) and the hydrogen negative ion current IEG(H-), IEG(e)/Ic(H-), decreases from 8.0 to 2.0 with an increase in the height of the electron fence (HEF), which is a filter that prevents electron diffusion from the extraction region.