Progress in long pulse production of powerful negative ion beams for JT-60SA and ITER

Kojima, Atsushi; Umeda, Naotaka; Hanada, Masaya; Yoshida, Masafumi; Kashiwagi, Mieko; Tobari, Hiroyuki; Watanabe, Kazuhiro; Akino, Noboru; Komata, Masao; Mogaki, Kazuhiko; Sasaki, Shunichi; Seki, Norikatsu; Nemoto, Shuji; Shimizu, Tatsuo; Endo, Yasuei; Oasa, Kazumi; Dairaku, Masayuki; Yamanaka, Haruhiko; Grisham, L. R.*

JAEA has developed the high-energy negative ion source for JT-60SA and ITER NBI in order to realize the long-pulse negative ion production/acceleration over 100 seconds. The key techniques to achieve the long pulse production of negative ions are control of the temperature of the Cs-covered plasma grid with the surface production of the negative ions. For this purpose, high temperature fluid is circulated in the PG to keep the temperature at 200C stationaly. This temperature control enanbles the negative ion production to be kept for 100 s with beam current of 15 A, which is the new record by 3 times longer than the previous one. In order to achieve the long pulse acceleration, new extrator having 5 times higher capability of allowable heat flux due to co-extracted electrons. This extractor also has the beam control to compensate the residual magnetic field in the ion source. By using this extractor 700 keV, 100A/m negative ion beams has been kept for 60s which is the limitation of the pulse length of the power supplies.