Production of H− ions by thermal desorption process

H− or D− ion current extracted from a hydrogen or deuterium discharge plasma can be substantially enhanced by introducing a small quantity of an alkaline metal, such as cesium, into the extraction region of the ion source. The increase in the extractable H− or D− current is accompanied by a large reduction in the electron output current. This phenomenon of H− or D− enhancement only occurs when the temperature of the plasma electrode is above 50 °C and reaches a maximum around 300 °C. New experimental results here demonstrate that thermal desorption of H atoms from the surface of an electrode together with a reduction of its surface work-function can account for the increase in H− output current observed in the cesium-seeded volume H− ion sources.