Development of a volume H- ion source for LAMPF

We have continued the development of a toroidal-filter volume H ^- ion source with the goal of providing a better ion source for the proton storage ring at the Los Alamos Neutron Scattering Center (LANSCE). A prototype source has produced H^- beam currents of 6.3 mA from a 3-mm-diameter emission aperture (89 mA/cm²) and 18 mA from a 10-mm-diameter emission aperture (23 mA/cm²). These results were achieved when cesium was added to tile discharge. The cesium increased the H^- current by a factor of 2-3 while the extracted electron current was strongly suppressed. The magnetic filter can be configured so that the electron to H^- ratio is 2:1 and is weakly dependent on operating parameters, with only a moderate loss of H^- current. Tests indicate there is essentially no explicit dependence of extracted beam current on duty factor up to 10% duty-factor. Emittance data were taken for various operating conditions in a mass-analyzed beam line and a comparison is made to the surface conversion H^- ion source now in operation for the storage ring