19th IAEA Fusion Energy Conference

Property of Alfven Eigenmode in JT-60U Reversed Shear and Weak Shear Discharges

M. Takechi¹⁾, A. Fukuyama²⁾, K. Shinohara¹⁾, M. Ishikawa³⁾, Y. Kusama¹⁾, S. Takeji¹⁾, T. Fujita¹⁾, T. Oikawa¹⁾, T. Suzuki¹⁾, N. Oyama¹⁾, T. Ozeki¹⁾, A. Morioka¹⁾, C. Z. Cheng⁴⁾, N. N. Gorelenkov⁴⁾, G. J. Kramer⁴⁾, R. Nazikian¹⁾ and the JT-60 team¹⁾
1) Japan Atomic Energy Research Institute, Naka-machi 319-0193, Japan
2) Department of Nuclear Engineering, Kyoto University, Kyoto 606-8501, Japan.
3) Plasma Research Center, University of Tsukuba, Tsukuba-shi 305-8877, Japan.
4) Princeton Plasma Physics Laboratory, Princeton, NJ 08543, USA

Abstract.
This paper reports activity of Alfven eigenmode (AE) in the JT-60U reversed shear (RS) and weak shear (WS) plasmas. The AEs with a rapid frequency sweeping and then saturation of frequency as q_min decreases has been observed in low-β_h RS discharges with Negative-ion-based NBI (NNBI) or ICRH. We introduce the new type of AE which we call reversed-shear-induced Alfven Eigenmode (RSAE) near q_min. This puzzling frequency change can be explained by considering the properties of RSAE and their transition to toroidal Alfven Eigenmodes (TAEs). We verify the existence of RSAEs and their transition to TAEs from magnetic fluctuations and measured q-profile in JT-60U plasmas. The AE amplitude is maximum during this transition, e.g., ~2.4 < q_min min transition range of n = 1 AE to avoid substantial fast ion loss by large amplitude AEs in RS plasmas.