Development of DC ultra-high voltage insulation technology for ITER NBI

Tobari, Hiroyuki; Hanada, Masaya; Watanabe, Kazuhiro; Kashiwagi, Mieko; Kojima, Atsushi; Dairaku, Masayuki; Seki, Norikatsu; Abe, Hiroyuki; Umeda, Naotaka; Yamanaka, Haruhiko; Maejima, Tetsuya; Terunuma, Yuto; Kondo, Tatsuo; Tanaka, Shigeru*; Kadowaki, Makoto*; Yamaguchi, Kohei*; Decamps, H.*; Kuriyama, Masaaki*; Graceffa, J.*; Lennart, S.*; Hemsworth, R. S.*; Boilson, D.*

Progress on technical development on ITER and JT-60SA neutral beam injector (NBI) were reported. In development of a 1 MV insulating transformer for ITER NB power supply, a bushing extracting 1 MV required a huge insulator that was impossible to manufacture. To solve this issue, a composite bushing with FRP tube and a small condenser bushing with insulation gas was newly developed. In development the HV bushing as an insulating feed through, voltage holding in large cylindrical electrodes inside the HV bushing was investigated. The scaling for vacuum insulation design of large cylindrical electrodes was obtained. Toward long pulse production and acceleration of negative ion beam, active control system of plasma grid temperature and a new extractor consisting of the extraction grid with high water cooling capability and aperture offset were developed. As a result, 15 negative ion beam has been achieved for 100 s. Also beam energy density has been increased two orders of magnitude.