Surface–plasma negative ion source for the medicine accelerator (abstract)

Abstract

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