H− ion formation from a surface conversion type ion source

Abstract

Volume‐produced H⁻ ions have been extracted from a multicusp ion source. In addition, a molybdenum converter is installed in the source to generate surface‐produced H⁻ ions. Without cesium, the production of H⁻ ions by the surface process is very small compared with those generated by volume production. However, the presence of cesium can greatly enhance the surface production yield. The energy spectrum shows that the surface‐generated H⁻ ions contain two distinct groups when cesium is added to the discharge. The energy of one group is essentially that of the sheath potential and appears to be produced by a desorption process. The second group of H⁻ ions has a slightly higher energy and appears to be formed by a reflection process. Different types of converter materials have also been tested.