(EX/6-2) Confinement Degradation of Energetic Ions due to Alfvén Eigenmodes in JT-60U Negative-Ion-Based Neutral Beam Injection Plasmas

M. Ishikawa1), M. Takechi1), K. Shinohara1), G. Matsunaga1), Y. Kusama1), A. Fukuyama2), V. A. Krasilnikov3), Yu. Kashuck3), T. Nishitani1), A. M. Sukegawa1), M. Isobe4), M. Sasao5), JT-60 Team1)
1) Japan Atomic Energy Agency, Naka, Japan
2) Kyoto University, Kyoto, Japan.
3) Troitsk Institute of Innovating and Fusion Research, Troitsk, Russia
4) National Institute for Fusion Science, Toki, Japan.
5) Tohoku University, Sendai, Japan

Abstract.  Confinement degradation of energetic ions due to Alfvén Eigenmodes (AEs) induced by negative-ion-based neutral beam injection for the classical confinement is quantitatively evaluated for the first time. AEs, whose frequency rapidly sweeps and then saturates as the minimum value of the safety factor decrease, have been observed in JT-60U. These mode behavior can be explained by reversed-shear induced AE (RSAE) and the transition from RSAEs to TAEs. Measured total neutron emission rate (Sn) in the presence of these AEs is compared with that predicted by classical theory. As a result, confinement degradation of energetic ions is confirmed, especially, it is largest in the transition phase from RSAEs to TAEs, where the maximum reduction rate for the classical confinement is estimated as ( ΔSn/Sn)max∼45%. Line-integrated neutron emission profile is also compared with that predicted when assuming that the confinement is classical. The result indicates energetic ions are transported from core region of the plasma due to these AEs.

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