R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA

Kashiwagi, Mieko; Taniguchi, Masaki; Dairaku, Masayuki; DeEsch, H. P. L.*; Grisham, L. R.*; Svensson, L.*; Tobari, Hiroyuki; Umeda, Naotaka; Watanabe, Kazuhiro; Sakamoto, Keishi; Inoue, Takashi

At JAEA, a MAMuG (multi-aperture multi-grid) accelerator has been developed to perform required R&D for the ITER neutral beam system. H ion beam current was increased to 0.32 A (the ion current density (J) of 140 A/m) at the beam energy(Vb) of 796 keV. After the high power beam operation, pulse length was successfully extended from 0.2 s to 5 s at 550 keV, which yielded 131 mA H ion beam as an initial test of the long pulse operation. A test of a SINGAP (single-aperture single-gap) accelerator was performed at JAEA under an ITER R&D task agreement so as to compare the SINGAP and the MAMuG. The MAMuG accelerator was defined as the baseline design for ITER, due to advantages in its better voltage holding and less electron acceleration. In three dimensional beam trajectory analyses, aperture offset was found effective for compensation of beamlet deflection due to their own space charge and beamlet focusing.