EX/1-3 ·Steady State High betaN Discharges and Real-Time Control of Current Profile in JT-60U
T. Suzuki1), A. Isayama1), Y. Sakamoto1), S. Ide1), T. Fujita1), H. Takenaga1), T.C. Luce2), M.R. Wade3), T. Oikawa1), O. Naito1), S. Sakata1), M. Sueoka1), H. Hosoyama1), M. Seki1), N. Umeda1), T. Ozeki1), K. Kurihara1), T. Fujii1), T. Yamamoto1), JT-60 Team1)
1) Japan Atomic Energy Research Institute, Naka, Japan
2) General Atomics, San Diego, USA
3) Oak Ridge National Laboratory, Oak Ridge, USA
Abstract: The period with high bN has been extended remarkably in JT-60U. bN=3 was sustained for 6.2s and bN=2.1 for 20 s, only interrupted by the limit of neutral beam heating system, with low safety factor (q95=2.2 and 3.2, respectively). In the case of bN=2.1, in particular, the current profile reached a steady state. In this low safety factor regime, the resonant surfaces with q=3/2 and 2/1 were shifted outside the steep pressure gradient layer, stabilizing the neoclassical tearing mode (NTM) above the previous bN-limit imposed by NTMs. To establish the feedback control of the safety factor profile q(r), a real-time q(r) control system has been developed using the motional Stark effect (MSE) diagnostic as detector and the lower hybrid current drive (LHCD) as actuator. For the first time, real-time feedback control has been demonstrated based on local pitch angle measurement and control of parallel refractive index of LH waves adjusting the LHCD location.
Keywords: beta value, current drive, current profile control, high performance experiments, steady state operation,