Formulation and verification of multiscale gyrokinetic simulation of kinetic-MHD processes in toroidal plasmas

A comprehensive gyrokinetic simulation model has been implemented in the global toroidal gyrokinetic code and verified for studying low-frequency waves and turbulence in magnetic fusion plasmas by treating all kinetic-MHD processes on an equal footing. A theoretical framework has been formulated to unify various methods for efficiently solving the electron drift kinetic equation in multiscale simulations by separating electron responses into analytic and non-analytic parts based on the smallness parameter of electron-to-ion mass ratio. The model can be reduced to the ideal MHD model with both the linear dispersion relation and the nonlinear ponderomotive force in theory and simulation. The model is used for the verification and validation of simulating internal kink modes in the DIII-D tokamak with accurate calculations of equilibrium parallel current and compressible magnetic perturbation. A large simulation database has been generated to train a surrogate model to predict the kink instability. Statistical analysis shows that the radial location of safety factor q = 1 flux surface, the pressure gradient, the minimum q value, and the plasma beta inside the q = 1 surface are the most important parameters for predicting the kink instability.