Influence of cesium on the emission of negative hydrogen ions from a reflex discharge source

Steady beams of negative hydrogen ions with current density j- ∼ 100 mA/cm2, total current I- ∼ 10 A, and energy ev0 ∼ 1.5 MeV are needed for neutral-particle injectors in thermonuclear fusion devices. In particular, double-chamber sources are now being designed, in which the H- ion generation takes place in the plasma volume due to dissociative attachment of electrons to vibrationally excited H2 molecules. The addition of cesium vapor to such sources enhances the H- ion yield. Here, theoretical and experimental investigations are done on the influence of cesium on the H- ion emission from a reflex source. It is shown that with the addition of cesium vapor in the discharge the main contribution to H- ion production comes from processes which take place on the cesium-coated surface of the discharge chamber