Gyrokinetic modelling of non-linear interaction of Alfvén waves and EGAMs in ASDEX-Upgrade

Abstract Energetic particle (EP) dynamics and excitation of EP driven instabilities is an important topic of study for the physics of fusion reactors. In this paper we consider EPs injected in the plasma by neutral beams at high energies to heat it. EP species exist far from thermal equilibrium in the form of anisotropic non-Maxwellian distribution functions. EP driven modes, such as Alfvén waves (AWs) and EP driven geodesic acoustic modes (EGAMs), can redistribute EPs in phase-space and harm confinement. We examine the effects of experimental-like anisotropic EP distribution functions on the excitation and the non-linear coupling of such instabilities with the gyrokinetic particle-in-cell code ORB5. The growth rate of EGAMs is found to be sensitively dependent on the phase-space shape of the distribution function as well as on the non-linear wave-wave coupling with AWs. Experimental findings are compared with numerical results.