Noninductive Current Drive and Steady-State Operation in JT-60U

Studies on noninductive current drive (CD) and development of an integrated steady-state high performance operation in JT-60 are reviewed. Experiments on lower hybrid current drive (LHCD) in JT-60 have shown a large noninductive current up to 3.6 MA, high current drive efficiency of 3.5 × 10¹⁹ m^-2A/W, and a flexible current profile control. Basic studies on LH waves, such as an effect of accessibility condition, fast electron behaviors, and so on, in JT-60 have contributed to understanding LHCD physics. Significant progress in neutral beam current drive (NBCD) has been made in JT-60 by testing the performance of negative ion-based (N) neutral beam injection (NBI) (N-NBI). The CD efficiency of ~1.5 × 10¹⁹ m^-2A/W and negative ion-based neutral beam (N-NB) driven current of ~1 MA have been demonstrated in N-NBCD. Strongly localized noninductive driven current by electron cyclotron current drive (ECCD) was identified with a fundamental O-mode scheme from a low field side injection. ECCD in JT-60 has shown CD efficiency of 0.5 × 10¹⁹ m^-2A/W and EC-driven current of 0.2 MA. Modification of local current profile was demonstrated and was used for suppression of neoclassical tearing mode. Based on these developments, two integrated steady-state operation scenarios were developed in JT-60, which are reversed magnetic shear (R/S) plasmas and high p ELMy H-mode. In these operation regimes, discharges have been sustained near the steady-state current profile under full noninductive current drive (High p; HH_y2 ~ 1.4 and _N ~ 2.5 with N-NB, R/S; HH_y2 ~ 2.2 and _N ~ 2 with f_BS ~ 80%). High performance plasmas with a high n_DoET_io and at high normalized density were also produced under fully noninductive condition in high p ELMy H-mode and R/S mode.