H-ion formation from a surface conversion type ion source

Volume-produced H ions were extracted from a multicusp ion source by using a standard extraction system. In addition, a molybdenum converter is installed in the source to generate surface-produced H ions. The H ion yield is measured by a mass spectrometer. 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 have slightly higher energies and appear to be formed by a reflection process. Different types of converter materials were also tested.