18th IAEA Fusion Energy Conference

Reactor Relevant Current Drive and Heating by N-NBI on JT-60U

T. Oikawa, Y. Kamada, A. Isayama, T. Fujita, T. Suzuki, N. Umeda, M. Kawai, M. Kuriyama, L.R. Grisham^*), Y. Ikeda, K. Kajiwara , K. Ushigusa, K. Tobita, A. Morioka, M. Takechi, T. Itoh and the JT-60 TEAM
*) Princeton Plasma Physics Laboratory

Abstract.
Current drive capability of negative-ion-based NBI (N-NBI) in JT-60U has been extended to the reactor relevant regime. Driven current profile and current drive efficiency have been evaluated in the high temperature regime of central electron temperature T_e(0)~10keV, and reasonable agreement with theoretical prediction has been confirmed in this regime. N-NB driven current reached 1 MA with injection power of 3.75MW at beam energy of 360keV. The current drive efficiency of1.55x10¹⁹ Am^-2W^-1 approaching to the ITER requirement was achieved in the high b_p H mode plasma with T_e(0)~13keV. This current drive performance realized the sustainment of high beta (b_N=2.5) and high confinement (HH_y2=1.4) plasma in full current-driven condition at the plasma current of 1.5MA. The influence of instabilities on N-NB current drive was studied. When a burst like instability driven by N-NB occurred in the central region, reductions in loop voltage near magnetic axis and neutron production rate due to loss of beam ions were observed although the lost driven current was at most ~7% of the total driven current. When neoclassical tearing instability appeared in high beta plasmas, loss of beam ions was enhanced with increasing activity of instability and depended on the location of instability.