R&D on a high energy accelerator and a large negative ion source for ITER

Inoue, Takashi; Taniguchi, Masaki; Morishita, Takatoshi  ; Dairaku, Masayuki; Hanada, Masaya; Imai, Tsuyoshi*; Kashiwagi, Mieko; Sakamoto, Keishi; Seki, Takayoshi*; Watanabe, Kazuhiro

The R&D of a 1 MeV accelerator and a large negative ion source has been carried out at JAERI for the ITER NB system. The R&D is in progress at present toward: (1) 1 MeV acceleration of H ion beams at the ITER relevant current density of 200 A/m, and (2) improvement of uniform negative ion production over wide extraction area in large negative ion sources. Recently, H ion beams of 1 MeV, 140 mA level have been generated with a substantial beam current density (100 A/m). In the uniformity study, it has been clarified that electron temperature in the ion extraction region is locally high ( 1 eV), which resulted in destruction of negative ions at a high reaction rate. Interception of fast electrons leaking through a transverse magnetic field called "magnetic filter" has been found effective to lower the local electron temperature, followed by an improvement of negative ion beam profile.