Analytic stability boundaries for compressional and global Alfven eigenmodes driven by fast ions. I. Interaction via ordinary and anomalous cyclotron resonances.

Lestz, J. B. ; Gorelenkov, N. N. ; Belova, E. V. ; Tang, S. X. ; Crocker, N. A.
Issue date: 2019
Rights:
Creative Commons Attribution 4.0 International (CC BY)
Cite as:
Lestz, J. B., Gorelenkov, N. N., Belova, E. V., Tang, S. X., & Crocker, N. A. Analytic stability boundaries for compressional and global Alfven eigenmodes driven by fast ions. I. Interaction via ordinary and anomalous cyclotron resonances [Data set]. Princeton Plasma Physics Laboratory, Princeton University. https://doi.org/10.11578/1608300
@electronic{lestz_j_b_unknown,
  author      = {Lestz, J. B. and
                Gorelenkov, N. N. and
                Belova, E. V. and
                Tang, S. X. and
                Crocker, N. A.},
  title       = {{Analytic stability boundaries for compre
                ssional and global Alfven eigenmodes dri
                ven by fast ions. I. Interaction via ord
                inary and anomalous cyclotron resonances
                .}},
  publisher   = {{Princeton Plasma Physics Laboratory, Pri
                nceton University}},
  url         = {https://doi.org/10.11578/1608300}
}
Description:

Conditions for net fast ion drive are derived for beam-driven, sub-cyclotron compressional (CAE) and global (GAE) Alfven eigenmodes, such as those routinely observed in spherical tokamaks such as NSTX(-U) and MAST. Both co- and counter-propagating CAEs and GAEs are investigated, driven by the ordinary and anomalous Doppler-shifted cyclotron resonance with fast ions. Whereas prior results were restricted to vanishingly narrow distributions in velocity space, broad parameter regimes are identified in this work which enable an analytic treatment for realistic fast ion distributions generated by neutral beam injection. The simple, approximate conditions derived in these regimes for beam distributions of realistic width compare well to the numerical evaluation of the full analytic expressions for fast ion drive. Moreover, previous results in the very narrow beam case are corrected and generalized to retain all terms in omega/omega_{ci} and k_{||}/kperp, which are often assumed to be small parameters but can significantly modify the conditions of drive and damping when they are non-negligible. Favorable agreement is demonstrated between the approximate stability criterion, simulation results, and a large database of NSTX observations of cntr-GAEs.

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