Development of long pulse neutral beam injector on JT-60U for JT-60SA

Hanada, Masaya; Ikeda, Yoshitaka; Grisham, L.*; Kobayashi, Shinichi*; JT-60NBI Group

The paper reports the progress of R&D toward the JT-60SA at Japan Atomic Energy Agency (JAEA) during 2006-2008. Significant progress has been made in the long pulse operation of the negative-ion-based NBI (N-NBI) where a 10 MW D beam is required to be injected for 100s in JT-60SA. The injection pulse length has been successfully extended from 20s in the last campaign to 30s; the maximum heating time allowed in JT-60U. The achieved injection energy, defined as the product of the injection time and power, was successfully increased from 67 MJ in the last campaign to 80 MJ in the 2008 campaign by neutralizing 340 keV, 27 A D ion beam produced with two negative ion sources. The high injection energy was achieved by the reduction of the grid power loading to an allowable level. The direct interception of the D ions by acceleration grids was suppressed by tuning the steering angle of outermost beamlets with modified field shaping (FS) plates in the ion source. The modified FS plate succeeded in the reduction of the grid power loading to an allowable level for JT-60SA. Moreover, the power loading in the beamline, where the power of the electrons ejected from the JT-60U negative ion source is dissipated, was also confirmed to be low enough to extend the injection pulse length to 100s for JT-60SA.