Authors: E. D. Fredrickson, E. Belova, D. J.
Battaglia, R. E. Bell, N. A. Crocker, D. Darrow, A. Diallo, S.
Gerhardt, N. Gorelenkov, B. LeBlanc, M. Podestŕ and the NSTX-U
team
Abstract: In this paper we present data from experiments
on NSTX-U where it was shown for the first time that small amounts
of high pitch-angle beam ions can strongly suppress the
counter-propagating Global Alfvén Eigenmodes (GAE). GAE have been
implicated in the redistribution of fast ions and modification of
the electron power balance in previous experiments on NSTX. The
ability to predict the stability of Alfvén modes, and developing
methods to control them, is important for fusion reactor like the
International Tokamak Experimental Reactor (ITER) which are heated
by a large population of non-thermal, super-Alfvénic ions
consisting of fusion generated alphas and beam ions injected for
current profile control. A qualitative explanation of the GAE
suppression is presented, as well as the results of modeling the
GAE suppression with the HYM code. This paper provides a valuable
validation of our theoretical understanding of fast-ion-driven
instabilities and a promising demonstration of fast-ion driven
instabilities via modification of the fast-ion distribution.
Submitted to: Physical Review Letters
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