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S. Bernabei, M. G. Bell, R. Budny, D. Darrow,
E. D. Fredrickson, J. C. Hosea, R. Majeski,
E. Mazzucato, N. Gorelenkov1, C. K. Phillips,
J. H. Rogers2, G. Schilling, J. R. Wilson,
R. White, F. Zonca3, S. Zweben
Princeton Plasma Physics Laboratory, P.O. box 451,
Princeton N.J. 08543
1 TRINITI, Troitsk, Moscow, Russia 142 092
2 Intevac Inc., 3550 Basset St., Santa Clara, Ca. 95054
3 Associazione EURATOM-ENEA, CRE 00044 Frascati, Italy
Abstract. High power ICRF minority heating produces an energetic tail in the
distribution function of the resonant ions. When the energy in this tail
exceeds a certain threshold, various kinds of Alfvénic instabilities can be
excited. In TFTR, it is found that modes whose frequencies decrease vs.
time
cause fast ion losses and in turn a reduced Rf heating efficiency, unlike the
usual global TAE. The frequency decrease of the modes is found to correspond
to a radial movement of t he mode itself: modelling shows that this feature
causes an avalanche of fast ion losses due to a diffusion process. The
frequency-decreasing modes play a fundamental role in the stabilization of the
sawtooth and in its subsequent crash.
IAEA 2001
