Physics assessment of the NBI capability in ITER plasmas

Oikawa, Toshihiro; Polevoi, A. R.*; Mukhovatov, V.*; Sakamoto, Yoshiteru; Kamada, Yutaka; Shimada, Michiya*; Campbell, D. J.*; Chuyanov, V.*; Schunke, B.*; Tanga, A.*; Hemsworth, R. S.*

In the ITER design review, reducing the NBI energy is proposed for increasing the plasma rotation in terms of suppressing MHD instabilities. NBI capability has been assessed for various design possibilities. In D-T operation, the planned auxiliary heating power makes possible reliable operation well above the H-L transition boundary. In hydrogen operation the beam energy should be limited to 500keV due to the NBI shinethrough. However, reduction of the NBI central heating at high density necessary for the ITER mission is significant at 500keV, confirming the need for higher energy in DT operation. Although the rotation increases by 13% at 750keV relative to 1MeV at constant power, NB current drive decreases by 20%, which would be problematic for the development of steady-state scenarios. Therefore it is concluded that the beam energy should be kept 1MeV in DT operation. The beam energy variation in a pulse enables the plasma beta control for avoiding the stability boundary.