Voltage holding characteristics and new design of MeV accelerator

Taniguchi, Masaki; Kashiwagi, Mieko; Mizuno, Takatoshi; Umeda, Naotaka; Tobari, Hiroyuki; Kojima, Atsushi; Tanaka, Yutaka; Dairaku, Masayuki; Watanabe, Kazuhiro; Hanada, Masaya; Inoue, Takashi; Sakamoto, Keishi

In JAEA, Multi-Aperture Multi-Grid (MAMuG) accelerator called "MeV accelerator" has been developed for the neutral beam injector (NBI) of ITER. Up to now, 800 keV, 320 mA (140 A/m), 0.2 s and 750 keV, 221 mA (100 A/m), 5 s beam was successfully accelerated. To achieve 1 MeV, 200 A/m beam acceleration relevant to ITER, it is essential to improve the voltage holding of the accelerator. In the present work, voltage holding between grids of the MeV accelerator was studied by changing the gap length. As the result, following results were obtained; (1) Voltage holding is proportional to the square root of gap length (clump theory). (2) Voltage holding of the real accelerator is much lower than that of the ideal quasi-Rogowski grid. According to the results above, minimum gap length for the stable voltage holding of 200 kV (rated voltage for one stage of MeV accelerator) was determined to be 100 mm and modification of MeV accelerator is now in progress.