Energetic-particle-modified global Alfven eigenmodes

Lestz, J. B. ; Belova, E. V. ; Gorelenkov, N. N.
Issue date: 2017
Creative Commons Attribution 4.0 International (CC BY)
Cite as:
Lestz, J. B., Belova, E. V., & Gorelenkov, N. N. (2017). Energetic-particle-modified global Alfven eigenmodes [Data set]. Princeton Plasma Physics Laboratory, Princeton University. https://doi.org/10.11578/1562074
  author      = {Lestz, J. B. and
                Belova, E. V. and
                Gorelenkov, N. N.},
  title       = {{Energetic-particle-modified global Alfve
                n eigenmodes}},
  publisher   = {{Princeton Plasma Physics Laboratory, Pri
                nceton University}},
  year        = 2017,
  url         = {https://doi.org/10.11578/1562074}

Fully self-consistent hybrid MHD/particle simulations reveal strong energetic particle modifications to sub-cyclotron global Alfven eigenmodes (GAE) in low-aspect ratio, NSTX-like conditions. Key parameters defining the fast ion distribution function -- the normalized injection velocity v_0/v_A and central pitch -- are varied in order to study their influence on the characteristics of the excited modes. It is found that the frequency of the most unstable mode changes significantly and continuously with beam parameters, in accordance with the Doppler-shifted cyclotron resonances which drive the modes, and depending most substantially on v_0/v_A. This unexpected result is present for both counter-propagating GAEs, which are routinely excited in NSTX, and high frequency co-GAEs, which have not been previously studied. Large changes in frequency without clear corresponding changes in mode structure could indicate the existence of a new energetic particle mode, referred to here as an energetic-particle-modified GAE (EP-GAE). Additional simulations conducted for a fixed MHD equilibrium demonstrate that the GAE frequency shift cannot be explained by the equilibrium changes due to energetic particle effects.

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