Gyrokinetic Simulation of Energetic Particle Turbulence and Transport

The fully self-consistent simulation of energetic particle turbulence and transport in burning plasmas such as ITER must incorporate three new physics elements: (i) kinetic effects of thermal particles at the thermal ion gyroradius (micro scale), (ii) nonlinear interactions of many meso scale (energetic particle gyroradius) shear Alfvén waves induced by the kinetic effects at the micro scale, and (iii) meso-micro couplings of the microturbulence and Alfvénic fluctuations. The large dynamical ranges of spatial-temporal processes further require global simulation codes efficient in utilizing massively parallel computers at the petascale level and beyond. Therefore, the studies of energetic particle physics in ITER burning plasmas call for a gyrokinetic turbulence approach. Progress of gyrokinetic simulations of energetic particle turbulence and transport in tokamaks is reported in this paper. Specifically, nonlinear gyrokinetic simulations find that the energetic particle transport induced by the microturbulence decreases rapidly due to the averaging effects of the large gyroradius and banana width, and the fast decorrelation of energetic particles with waves. Linear global gyrokinetic simulations using GTC and GYRO demonstrate the excitation of the toroidal Alfvén eigenmode (TAE) by the pressure gradient of the energetic particles. The TAE linear dispersion from gyrokinetic simulations is in reasonable agreement with conventional fluid simulations. Furthermore, initial linear and nonlinear simulations of a DIII-D experiment dedicated for energetic particle studies find fast ion instabilities.