Linearized gyrofluid model of the alpha-destabilized toroidal Alfvén eigenmode with continuum damping effects

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Abstract
The toroidicity‐induced shear Alfvén eigenmode (TAE) can be destabilized by energetic particle populations through inverse Landau damping. It may also be significantly damped by coupling with adjacent shear Alfvén continua. A gyrofluid model with Landau closure that includes both of these effects is developed and applied to this instability. The model consists of the usual reduced magnetohydrodynamic (MHD) equations for the evolution of the poloidal flux and toroidal component of vorticity, coupled with equations for the density and parallel velocity moments of the energetic species. The latter two equations include Landau damping/growth effects through use of a consistent closure relation, which is equivalent to a two‐pole approximation to the plasma dispersion function. These equations are solved numerically using a three‐dimensional initial value code (t a e / f l) in toroidal geometry. The unstable TAE growth rate and continuum damping rates are compared with recent analytical estimates, and reasonable agreement is obtained.