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(EX8/6) Alfvén eigenmodes and their Impact on Plasma Characteristics in JT-60U

Y. Kusama, R. Nazikian, G. J. Kramer, H. Kimura, M. Saigusa, T. Ozeki, G. Y. Fu, K. Tobita, T. Oikawa, K. Shinohara, T. Kondoh, M. Moriyama, F. V. Tchernychev, M. Nemoto, A. Morioka, M. Iwase, N. Isei, T. Fujita, S. Takeji, M. Kuriyama, C. Z. Cheng, K. W. Hill, and the JT-60 Team

Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Naka-machi, Naka-gun, Ibaraki-ken, 311-0193, Japan

Abstract.  In weak or reversed magnetic shear plasmas of JT-60U, the excitation and the stabilization of Alfvén eigenmodes and their impact on energetic ion confinement were investigated with the negative-ion- based neutral beam injection at 330-360 keV. Toroidicity-induced Alfvén eigenmodes (TAEs) were observed in weak shear plasmas with $\langle$$\beta_{\mathrm{h}}^{}$$\rangle$$\ge$0.1% and 0.4$\le$v_b||/v_A$\le$1. The stability of TAEs is consistent with the predictions by the NOVA-K code. New burst modes and chirping modes were observed at a higher beta regime of $\langle$$\beta_{\mathrm{h}}^{}$$\rangle$$\ge$0.2%. The effect of TAEs, burst modes and chirping modes on the fast ion confinement is small so far. The strongly-reversed shear plasma with the internal transport barrier suppresses Alfvén eigenmodes.

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