NBI:核融合炉に向けた物理•工学の進展 5.核融合炉用負イオン源•加速器の開発の現状

This article reviews R&D progress of a MeV accelerator and a large negative ion source at the Japan Atomic Energy Research Institute (JAERI). The JAERI MeV accelerator at present aims at acceleration of high current density (200 A/m2) H- ion beams up to MeV range energy. According to the progress of vacuum insulation technology, the MeV accelerator sustained 1 MV for more than two hours stably, followed by beam acceleration experiments of high current density. So far, H- ions beams of 146 A/m2, 836 keV have been obtained, which is the world's first demonstration of “ITER class” high power density beams. Recent investigation of negative ion uniformity in a large negative ion source revealed fast electron leakage through a magnetic filter, followed by destruction of negative ions in the local extraction region during pure volume (without Cs) operation. On the other hand, the leaked fast electrons enhance surface production of negative ions locally under Cs seeded operation. This implies possible high current density and uniform negative ion production by a high-density plasma in the magnetic configuration like positive ion sources, to be coupled with RF driven plasma production for an NB system of a fusion DEMO reactor.