Energy analysis of H− ions from a hollow-discharge duoplasmatron

Energy spectra of H− ions from a HDD source operating in mixtures of helium, hydrogen, and cesium reveal that negative ions are generated by a volume process and by a surface process. A marked difference was observed in the pressure dependence of the low- and high-energy groups, corresponding to the volume and the surface processes, respectively. The active surfaces could be identified. Some evidence that, besides collisional attachment processes, ion-molecular reactions have an influence on the yield of H− ions in volume reactions could be found.