Author: George J. Wilkie
Requested Type: Pre-Selected Invited
Submitted: 2018-02-28 02:57:59
Co-authors: I. G. Abel, A. Iantchenko, E. Highcock, I. Pusztai, T. Fülöp
Chalmers University of Technology
Chalmers Department of Physics
Fast ions are both affected by, and have an impact on, drift-wave microturbulence. The gyrokinetic equation is greatly simplified and admits an analytic solution in the energetic limit. The simplified solution accurately reproduces the high-energy transport in fully nonlinear turbulence. This transport can have an effect on the velocity-space distribution of fast ions, and an analytic modified slowing-down distribution has been derived that approximately captures this effect. Bulk plasma heat transport has also been observed in some circumstances to be sensitive to the presence of fast ions. Further approximations yield a reduced model for this effect. We show that this is directly related to the sensitivity of microturbulence to the ion-electron temperature ratio. An effective temperature ratio has been derived which mimics to the presence of fast ions in the high energy and strongly-ballooning limit. This model has been benchmarked against linear and nonlinear gyrokinetic simulations and explains several features of the fast ion stabilization of ITG microturbulence.