Effects of Fast Particles on MHD and Drift Waves
J. Weiland, T. Rafiq, C. Wilson, E. Schuster
Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)
Spokane, WA, USA, October 17-21, 2022
The purpose of the present work is to include the effects of fast
particles in our present fluid model for tokamak transport. This means
that the model will no longer be reactive to frequencies approaching
the precession frequency of fast particles. In order to obtain a smooth
transition, we also include resonance broadening as suggested in Ref. [1].
The theories of fast particles as usually implemented in MHD model and
the fluid description of drift waves have been combined, including the
effect of resonance broadening as given by Ghantous et al. [1]. As it is
easily seen from theories of Fishbone instabilities [2], the evaluation
of the kinetic resonance gives a factor as the ratio of mode frequency to
precession frequency in front of the resonance. This means that the fast
particle resonance can be ignored at the typical drift wave frequencies.
As we find, resonance broadening can be seen as having waves trapped in
the velocity distribution. Just as particle trapping in waves, the
trapping of waves reduces the resonance. In particle trapping, we need a
source in velocity space like an external neutral beam or nuclear reactions
to maintain the resonance. The same is true for wave trapping. This is
why Ghantous et al. [1] find that resonance broadening reduces the effect
of the resonance. We have verified this effect in a two-fluid description
of drift wave transport that includes fast particles.
*Supported by the US DOE DE-SC0013977.
