Kinetic-MHD simulation of mode frequency chirping in tokamaks and stellarators using M3D-C1*

This study focuses on investigating the occurrence of non-symmetric frequency chirping in energetic particle-driven MHD instabilities, which is commonly observed in both tokamaks and stellarators. The kinetic-MHD simulation code M3D-C1 is utilized to examine the toroidal Alfvén eigenmode (TAE) in NSTX and the geodesic acoustic mode (GAM) in LHD. M3D-C1, equipped with a kinetic module based on particle-in-cell method, enables the simulation of various types of MHD modes driven by energetic particles. Recently, the code has undergone upgrades to accommodate stellarator geometry. In the NSTX simulations, the down-chirping of the mode is found to be associated with resonant particles moving outward from the core. As these particles migrate to regions with stronger perturbed fields, the mode undergoes amplification during the down-chirping process. The symmetric breaking of the two chirping branches is influenced by the saturation level of the mode and the number of particles encompassed within the resonance region. On the other hand, in the GAM simulation  for LHD with a monotonic decreasing q profile, a dominant up-chirping branch of the mode is observed. Additionally, the paper will present results from nonlinear simulations of Alfvén mode driven by high-energy runaway electrons in DIII-D post-disruption scenarios.