Application of LHCD to sustainment and control of a reversed magnetic shear plasma in JT-60U

In JT-60U, it has been demonstrated experimentally that, by using lower hybrid current drive (LHCD), reversed magnetic shear can be maintained for a long period (7.5 s) and can be controlled non-inductively. The formation of a reversed magnetic shear configuration by a lower hybrid wave (LHW) injection alone was attempted and successfully achieved. Strongly reversed magnetic shear, even stronger than that formed by a normal scenario (NBI heating at current ramp-up), with a large area of shear reversal, was formed by the LHW alone. Moreover, the attainable βN, the normalized plasma beta, in this discharge was found to be comparable to that of a normal reversed shear discharge. Further more, the experimental results show that the area of good confinement can be changed, in coincidence with the reversed magnetic shear control by LHCD. In view of the recent success in improving plasma performance in reversed magnetic shear discharges with high power heating in TFTR, D-IIID and JT-60U, these results should not only affect the enhancement of performance but also the study of the physics involved. Recent results of JT-60U LHCD experiments with reversed magnetic shear plasmas are described in the paper. (author)