Mitigation of Alfven activity by 3D magnetic perturbations on NSTX

Kramer, G. J. ; Bortolon, A. ; Ferraro, N. M. ; Spong, D. A.; Crocker, N. A.; Darrow, D. S. ; Fredrickson, E. D. ; Kubota, S.; Park, J.-K. ; Podesta, M. ; Heidbrink, W. W.
Issue date: 2016
Creative Commons Attribution 4.0 International (CC BY)
Cite as:
Kramer, G. J., Bortolon, A., Ferraro, N. M., Spong, D. A., Crocker, N. A., Darrow, D. S., Fredrickson, E. D., Kubota, S., Park, J.-K., Podesta, M., & Heidbrink, W. W. (2016). Mitigation of Alfven activity by 3D magnetic perturbations on NSTX [Data set]. Princeton Plasma Physics Laboratory, Princeton University.
  author      = {Kramer, G. J. and
                Bortolon, A. and
                Ferraro, N. M. and
                Spong, D. A. and
                Crocker, N. A. and
                Darrow, D. S. and
                Fredrickson, E. D. and
                Kubota, S. and
                Park, J.-K. and
                Podesta, M. and
                Heidbrink, W. W.},
  title       = {{Mitigation of Alfven activity by 3D magn
                etic perturbations on NSTX}},
  publisher   = {{Princeton Plasma Physics Laboratory, Pri
                nceton University}},
  year        = 2016,
  url         = {}

Observations on the National Spherical Torus eXperiment (NSTX) indicate that externally applied non-axisymmetric magnetic perturbations (MP) can reduce the amplitude of Toroidal Alfven Eigenmodes (TAE) and Global Alfven Eigenmodes (GAE) in response to pulsed n=3 non-resonant fields. From full-orbit following Monte Carlo simulations with the 1- and 2-fluid resistive MHD plasma response to the magnetic perturbation included, it was found that in response to MP pulses the fast-ion losses increased and the fast-ion drive for the GAEs was reduced. The MP did not affect the fast-ion drive for the TAEs significantly but the Alfven continuum at the plasma edge was found to be altered due to the toroidal symmetry breaking which leads to coupling of different toroidal harmonics. The TAE gap was reduced at the edge creating enhanced continuum damping of the global TAEs, which is consistent with the observations. The results suggest that optimized non-axisymmetric MP might be exploited to control and mitigate Alfven instabilities by tailoring the fast-ion distribution function and/or continuum structure.

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