Suppression of Alfvén modes on NSTX-U with outboard beam injection

Fredrickson, E. D. ; Belova, E. V. ; Battaglia, D. J. ; Bell, R. E. ; Crocker, N. A.; Darrow, D. S.; Diallo, A. ; Gerhardt, S. P. ; Gorelenkov, N. N. ; LeBlanc, B. P. ; Podesta, M.
Issue date: 2017
Creative Commons Attribution 4.0 International (CC BY)
Cite as:
Fredrickson, E. D., Belova, E. V., Battaglia, D. J., Bell, R. E., Crocker, N. A., Darrow, D. S., Diallo, A., Gerhardt, S. P., Gorelenkov, N. N., LeBlanc, B. P., & Podesta, M. (2017). Suppression of Alfvén modes on NSTX-U with outboard beam injection [Data set]. Princeton Plasma Physics Laboratory, Princeton University.
  author      = {Fredrickson, E. D. and
                Belova, E. V. and
                Battaglia, D. J. and
                Bell, R. E. and
                Crocker, N. A. and
                Darrow, D. S. and
                Diallo, A. and
                Gerhardt, S. P. and
                Gorelenkov, N. N. and
                LeBlanc, B. P. and
                Podesta, M.},
  title       = {{Suppression of Alfvén modes on NSTX-U wi
                th outboard beam injection}},
  publisher   = {{Princeton Plasma Physics Laboratory, Pri
                nceton University}},
  year        = 2017,
  url         = {}

In this paper we present data from experiments on NSTX-U where it is 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. We present a qualitative interpretation of these observations using an analytic model of the Doppler-shifted ion-cyclotron resonance drive responsible for GAE instability which has an important dependence on k⊥ρL. A quantitative analysis of this data with the HYM stability code predicts both the frequencies and instability of the GAE prior to, and suppression of the GAE after the injection of high pitch-angle beam ions.

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