Short wavelength geodesic acoustic mode excitation by energetic particles

Abstract

Taking the collisionless damping of the geodesic acoustic mode (GAM) in the short wavelength limit originally investigated in [Z. Qiu et al., Plasma Phys. Controlled Fusion 51, 012001 (2009)] as an example, the physics processes underlying wave particle resonances in the short wavelength limit are clarified. As an illustrative application, GAM excitation by energetic particles in the short wavelength limit is investigated assuming a single pitch angle slowing-down fast ion equilibrium distribution function. Conditions for this energetic particle-induced GAM to be unstable are discussed.