Verification and validation of gyrokinetic and kinetic-MHD simulations for internal kink instability in DIII-D tokamak

TL;DR

This study compares gyrokinetic and kinetic-MHD simulations of the internal kink instability in a DIII-D tokamak, demonstrating their agreement and exploring the effects of magnetic perturbations and kinetic effects on the instability.

Contribution

It provides a comprehensive verification and validation of gyrokinetic and kinetic-MHD codes against experimental data for the internal kink mode in tokamaks.

Findings

Excellent agreement in growth rates and mode structures between codes.

Magnetic perturbations destabilize the kink mode.

Kinetic effects of ions influence the growth rate differently in the two models.

Abstract

Verification and validation of the internal kink instability in tokamak have been performed for both gyrokinetic (GTC) and kinetic-MHD codes (GAM-solver, M3D-C1-K, NOVA, XTOR-K). Using realistic magnetic geometry and plasma profiles from the same equilibrium reconstruction of the DIII-D shot #141216, these codes exhibit excellent agreement for the growth rate and mode structure of the internal kink mode when all kinetic effects are suppresed. The simulated radial mode structures agree quantitatively with the electron cyclotron emission measurement after adjusting, within the experimental uncertainty, the safety factor q=1 flux-surface location in the equilibrium reconstruction. Compressible magnetic perturbations strongly destabilize the kink, while poloidal variations of the equilibrium current density reduce the growth rate of the kink. Furthermore, kinetic effects of thermal ions are found to decrease the kink growth rate in kinetic-MHD simulations, but increase the kink growth rate in gyrokinetic simulations, due to the additional drive of the ion temperature gradient and parallel electric field. Kinetic thermal electrons are found to have negligible effects on the internal kink instability.