Acceleration of 100 A/m negative hydrogen ion beams in a 1 MeV vacuum insulated beam source

Taniguchi, Masaki; Inoue, Takashi; Kashiwagi, Mieko; Hanada, Masaya; Watanabe, Kazuhiro; Seki, Takayoshi*; Sakamoto, Keishi

The accelerator for the ITER NB system is required to produce 1 MeV, 40 A D-ion beams for 16.5 MW neutral beam injection per module. In the ITER NB system, conventional gas insulated beam source cannot be adopted because of the radiation-induced conductivity of the insulation gas. Thus a vacuum insulated beam source (VIBS), where the whole beam source is immersed in vacuum, had been developed in JAERI. Recently, voltage holding capability of the VIBS was drastically improved by installing the large stress ring, which reduces the electric field concentration at the negative side triple junction. Having improved the voltage holding capability of the VIBS, the H ion beams were extracted with seeding cesium to enhance the negative ion currents. Up to now, we had been succeeded in accelerating the H beam of 102 A/m (140 mA) at 800 keV. The beam acceleration was quite stable and accomplished for several hundreds shots in several experimental campaigns.