Development of continuous wave high voltage negative ion beam injector for tandem accelerator

A vacuum-insulated tandem accelerator, delivering the continuous wave 8 mA, 2 MeV proton beam, is operated regularly at the Budker Institute of Nuclear Physics, where a 10 mA, 25 keV negative ion injector is used. Recently, a new injector with an upgraded negative ion source and beam preacceleration has been developed to increase the tandem accelerated current. The transport line of the new injector is composed of a bending magnet with 90° ion beam turn, an acceleration tube for negative ion acceleration to the energy up to 150 keV, and a 0.6 m long transport section. The H^- ion beam production, its acceleration, and transport were studied at a test stand, which is equipped with electrical and optical diagnostics. The data on 14 mA, 133 keV continuous wave negative ion beam production and transport are presented. The undesirable coacceleration of secondary electrons, produced in the acceleration tube, was recorded as well. The coaccelerated electrons' current contributed up to 2% of the total accelerated beam at the operational vacuum in the low energy beam transport. The coaccelerated electrons were removed from the beam with a magnetic filter. The numerical modeling of the beam transport was carried out. A reasonable agreement between the modeled and experimental data was obtained.