Confinement degradation of energetic ions due to Alfvn eigenmodes in JT-60U negative-ion-based neutral beam injection plasmas

Ishikawa, Masao; Takechi, Manabu; Shinohara, Koji; Matsunaga, Go; Kusama, Yoshinori; Fukuyama, Atsushi*; Krasilnikov, V. A.*; Kashuck, Yu.*; Nishitani, Takeo; Morioka, Atsuhiko; et al.

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03

http://www-naweb.iaea.org/napc/physics/fec/fec2006/html/node279.htm#55502

Confinement degradation of energetic ions due to Alfvn Eigenmodes (AEs) induced by negative-ion-based neutral beam injection for the classical confinement is quantitatively evaluated for the first time. AEs, whose frequency largely sweep with the time scale of a few hundreds millisecond 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 AEs (RSAEs). Measured total neutron emission rate (Sn) in the presence of the AEs is compared with that predicted by a classical theory. As a result, confinement degradation of energetic ions is confirmed, 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. Further, changes in energy distribution of charge exchange neutral fluxes suggest radial transport is due to the resonance interaction between energetic ions and AEs.