18.8. Surface-Plasma Negative Ion Source for the Medicine Accelerator

Y.I. Belchenko, E.V. Grigoryev, Budker Institute of Nuclear Physics, Russia

E-mail: belchenko@inp.nsk.su

A neutron source for Boron Capture Neutron Therapy is under development at Budker Institute of Nuclear Physics. It bases on a tandem vacuum-isolated accelerator using a dc negative hydrogen ion source. A Compact dc ion source Model (CM) having reliable operation and a simplified maintenance was developed at BINP as a prototype of the high current source for medicine accelerator. CM uses a glow discharge with modified Penning geometry of electrodes and explores a surface-plasma negative ion production on the cesiated anode surface. CM optimal parameters are following: discharge voltage 60-80 V, discharge current up to 6 A, hydrogen pressure 4-5 Pa, cesium consumption <1 mg/hour, transverse magnetic field 0.5-1 kGs, optimal anode temperature 250-350 C. A build-in heater provides the CM quick start and simplifies the CM electrodes conditioning. CM delivers Nl beam with current 5 mA, beam energy 17 keV, normalized emittance of about 0.3 p mm-mrad, emission current density of about 0.1 A/cm2. Nl beam current is directly proportional to the discharge current and to the emission hole area. CM quick start and the stable dc operation for several hour runs was multiply tested. No essential erosion of electrodes was recorded.