Achievement and improvement of the JT-60U negative ion source for JT-60 super advanced

Kojima, Atsushi; Hanada, Masaya; Tanaka, Yutaka; Inoue, Takashi; Watanabe, Kazuhiro; Taniguchi, Masaki; Kashiwagi, Mieko; Umeda, Naotaka; Tobari, Hiroyuki; Grisham, L. R.*; JT-60NBI Group

The negative-ion based NB injectors on JT-60U achieved maximum injection power of 5.8 MW for 0.9 s via a neutralization of 400 keV, 35 A D ion beams produced in two ion sources. Furthermore, D beams of 3.4 MW were injected for 20 s using two negative ion sources. The pulse length was limited by power load on the acceleration grids. Reducing the grid power load to an allowable level, long pulse injections was achieved for 30 s at 3 MW. For JT-60SA, 500 keV, 22 A, 100 s beams are required. However, the achieved highest beam energy has been limited to 415 keV. To improve the voltage holding capability, the gap extension and the optimization of the structures have been designed in order to mitigate the local electric field. As a result, the voltage holding capability of 500 kV has been demonstrated. Furthermore, 490 kV for 40 s has been sustained without breakdown. The demonstration of the 500 keV beam acceleration is planned in September 2009 using the modified ion source.