Effect of a converter electrode in a multicusp negative ion source

The electron temperature of a negative ion source has to be low so as not to destroy produced negative ions by electron impact processes. The bulk plasma characteristics of a multicusp negative ion source with a converter electrode are examined by a probe data acquisition system for two cases; converter with cesium and converter without cesium. The effects of the converter bias on bulk plasma parameters were observed when cesium is not introduced. Under cesiated discharge condition, the converter bias effects are obscure. The addition of cesium into a helium discharge decreases the high energy electron component, which is unfavorable from a view point of negative ion extraction, and hence lowers the electron temperature.