Negative ion source improvement by introduction of a shutter mask

Studies of a multicusp source were recently done at the National Institute for Fusion Science by plasma grid masking. The maximal H− ion yield is ∼1.4 times greater for the shutter mask case than that for the standard source. Negative ion current evolution during the cesium feed to the masked plasma grid evidenced that about 60% of negative ions are produced on the shutter mask surface, while about 30% are formed on the plasma grid emission hole edges, exposed by cesium with the mask open.