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(EX/W-6) Property of Alfvén 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. Nazikian4), JT-60 Team1)
1) Japan Atomic Energy Research Institute, Naka-machi, Japan
2) Department of Nuclear Engineering, Kyoto University, Japan.
3) Plasma Research Center, University of Tsukuba, Japan.
4) Princeton Plasma Physics Laboratory, Princeton, USA

Abstract.  This paper reports results of Alfvén eigenmode (AE) experiments in the JT-60U reversed shear (RS) and weak shear (WS) plasmas. The observation of rapid frequency chirping modes in low- $ \beta_{h}^{}$ RS discharges with Negative-ion-based NBI (NNBI) or ICRH can be explained by considering the properties of reversed-shear-induced AE (RSAE) near qmin and their coupling to toroidal AEs (TAEs). We verify the existence of RSAEs and their coupling to TAEs for the first time from magnetic fluctuations and measured q-profile in JT-60U plasmas. Significant drop of the neutron emission rate and increase in fast neutral fluxes have been observed during the presence of bursting modes with large amplitude (ALE: Abrupt Large-amplitude Event) in high- $ \beta_{h}^{}$ WS plasmas. The recently installed diagnostic of a neutron emission profile measurement reveals the transport of energetic ions associated with bursting modes.

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IAEA 2003