The effects of cesium equilibrium on H− ion beam production with LANSCE surface converter ion source

We present a theoretical and experimental study on the effects of the plasma chamber wall temperature on the performance of the LANSCE (Los Alamos Neutron Science Center) surface conversion H− ion source. It was observed that increasing the chamber wall temperature can increase the extracted beam currents by several tens of percent. This observation motivated our investigations of the underlying mechanism, and we came to the conclusion that the effect depends on enhanced sputtering of H− from the cesiated converter electrode due to increased cesium vapor pressure. After discussing these mechanisms in detail, we present a simple and cost-effective technique how to control the chamber wall temperature by increasing the temperature of the cooling water supply for the plasma chamber. This technique can be applied in the near-term future to boost the performance of the LANSCE H− ion source.