Reflection of hydrogen atoms from alkali and alkaline earth oxide surfaces

Negative hydrogen ions were produced by scattering thermal energy H atoms with a Maxwellian distribution, from converter surfaces consisting of thick coatings of barium oxide, a mixture of cesium oxides and cesium carbonate, cesium oxides produced by decomposition of cesium carbonate, and submonolayer coatings of cesium on polycrystalline Mo. The H− ion yields and the ratio of electrons to ions were measured as a function of the incident H atom temperature for each of the converter surfaces. The ion yield and the electron to ion ratio were found to depend strongly on the temperature of the incident H atoms, and on the work function of the surface. The best results were obtained with the cesium oxide converter. H− yields from the cesium oxide were above 1% at H atom temperatures above 0.22 eV, and the surface was stable in a flux of atomic hydrogen of 1016 atoms/cm2/s for over 20 h of exposure time with no deterioration in performance.