Physical Insights and Test Stand Results for the LANSCE H- Surface Converter Source

The Los Alamos Neutron Science Center (LANSCE) H- surface converter source upgrade project has been ongoing for several years to reach 25-40 mA current with 7(cm-mrad) lab emittance (95% beam fraction). The duty factor is 12% (120 Hz, 1ms pulse length). Summary test stand results and interpretations for a six filament axial extraction H- source are presented. This source did produce 40-mA H- current, but with unacceptable emittance growth. More recently a fourth modified LANSCE H- production source with radial H- extraction system has been constructed, and is presently undergoing tests. Currents up to 25mA H- have been observed with 20% emittance growth. This emittance growth may be acceptable for 800 MeV linac operations. A summary of physical principles of emittance growth mechanisms and converter physics are given.