Design of ion source for LANSCE upgrade

The upgrade of the Los Alamos Neutron Science Center (LANSCE) Facility will require high intensity H^- beams. Lawrence Berkeley National Laboratory (LBNL) has been contracted by Los Alamos to develop an H^- ion generator that will meet the LANSCE upgrade requirements. H^- current is to be increased from the present 18 mA to 40 mA. The current LANSCE ion source uses surface conversion process and extracts ions radially. Two tungsten filaments are used as cathodes. The ion source designed by LBNL is also a surface conversion type source but the ions are extracted axially. This design allows six or more tungsten filaments to be installed radially so that the magnetic field of the permanent magnets on the cylindrical wall provides a magnetic filter field. This filter field prevents energetic electrons from entering the central plasma region where they could strip the H^- ions. The LBNL designed ion source has been operated successfully at the design parameters, 40 mA H at 12 % duty factor with 1 msec pulses. This paper describes the design and fabrication of the ion source