Optical diagnostics of negative ion beam transport.

A diagnostic complex for monitoring the position, propagation direction, and angular distribution dispersion of a particle beam planned for application in the Boron Neutron Capture Therapy facility is described in this paper. For the beam position and direction, the precision is, respectively, 0.1 mm and 1 mrad at 10 mA CW H- beam with energy of about 35 keV and a diameter of the order of 10 mm. The energy spread and angular divergence were measured within the accuracy of about 100 eV and 3 mrad, respectively. The acceptable precision of about 1 mm for the beam position is obtained at a relatively short exposure to 10 ms. To increase the radiation intensity of the beam, the addition of various gases was studied. The addition of gas decreases the beam width and increases the negative ions stripping.

Study of continuous wave 33 keV H- beam transport through the low energy beam transport section.

The transport of a continuous wave 33 keV negative ion beam through the low energy beam transport section, designed for beam injection into the tandem accelerator, was studied. The continuous wave H- beam, produced by the Penning surface-plasma source with hollow cathodes and cesium addition, was separated and focused by the 90° bending magnet and then transported through the 0.8 m long transport tube, equipped with beam electrical and optical diagnostics. The beam current was measured by a water-cooled Faraday cup at the transport tube exit. Beam sizes and profiles were measured by CCD cameras looking into the beam from the back and sides. The additions of hydrogen, argon, and xenon to the transport tube and to the bending magnet chamber in the pressure range of 10-6 to 10-4 Torr were tested. The influence of gas addition on the beam space charge compensation and beam transport was studied. A mechanism for the H- beam focusing due to space charge overcompensation and beam compression by the positive charge, produced with positive ion accumulation in the beam, is discussed.

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.