Acceleration of MeV-class energy, high-current-density H−-ion beams for ITER neutral beam system

Abstract

For the ITER neutral beam system, reasearch and development of a vacuum-insulated MeV accelerator has been carried out at Japan Atomic Energy Research Institute. After a successful 1MV insulation in vacuum for more than 2h, H−-ion-beam acceleration test is in progress to fulfill the ITER requirement of the current density of 200A∕m2 at 1MeV, with good beam optics quality of <7mrad divergence. For such a high-current-density H−-ion-beam acceleration, the Kamaboko negative-ion source was operated at high input power, with increased filament number and magnetic filter strength. The optimum perveance was investigated by scanning the extraction and acceleration voltages, together with the beam divergence measurement. As a consequence, H−-ion beams of 146A∕m2 (total ion-beam current: 206mA) were obtained at 836keV, of which power density is in the “ITER relevant” level. Such high-power-density beams with a divergence as low as 5mrad were obtained at the optimum perveance corresponding to that of the ITER (200A∕m2 at 1MeV).