Acceleration of 1 MeV, 100 mA class H ion beams in a proof-of-principle accelerator for ITER

Inoue, Takashi; Taniguchi, Masaki; Dairaku, Masayuki; Hanada, Masaya; Kashiwagi, Mieko; Morishita, Takatoshi; Watanabe, Kazuhiro; Imai, Tsuyoshi

The paper reports progress of proof-of-principle test of negative ion accelerator for ITER. The accelerator structure is immersed in vacuum, surrounded by a FRP insulator column as the vacuum boundary. So far, the beam energy has been limited due to poor voltage holding capability of the FRP insulator column. By lowering the electric field strength at the triple junction (interface of FRP insulator, metal flange and vacuum) with large stress ring installed inside the insulator column, high voltage of 1 MV was stably sustained for more than 2 hours. In the following beam test, acceleration of 900 keV, 100 mA H ion beam was succeeded. Although the current was lower (70 mA) at 1 MeV, the beam of this level has been stably accelerated for 6 days, 130 shots in total (each pulse length: 1 s).