(EX/6-4) Off-axis Current Drive and Current Profile Control in JT-60U

T. Suzuki1), S. Ide1), T. Fujita1), T. Oikawa1), M. Ishikawa1), N. Hayashi1), O. Naito1), M. Sueoka1), M. Seki1), JT-60 Team
1) Japan Atomic Energy Agency, Naka, Ibaraki-ken, 311-0193 Japan

Abstract.  For the first time, we have measured the current density profile for off-axis neutral beam current drive (NBCD), using motional Stark effect (MSE) diagnostic. A spatially localized NBCD profile was clearly observed at r/a=0.6-0.8. The location was also confirmed by multi-chordal neutron emission profile measurement. The total amount of the driven current (0.15MA) was consistent with the decrease in the surface loop voltage. The off-axis current drive can raise safety factor (q) in the center and help to avoid instability that limits performance of the plasma. We have developed a real-time control system of the minimum q ( qmin), using the off-axis current drive. Injection power of lower hybrid (LH) waves, and hence, its off-axis driven current controls qmin. In a high b plasma ( βN = 1.7, βp = 1.5), the system was adopted to control qmin. With the control, qmin was raised and MHD fluctuations were suppressed. The stored energy increased by 16% with the MHD fluctuations suppressed.

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