Development of the Gyrokinetic-MHD Hybrid Code cuGMEC and Its Nonlinear Simulations of Alpha Particle-driven Alfven Eigenmodes in ITER

We report the development of cuGMEC, a high-performance GPU-accelerated gyrokinetic-MHD hybrid code implemented in CUDA C++ in addition to its CPU version [1], along with its nonlinear simulation results for ITER. In cuGMEC, electrons are treated as a fluid, energetic particles and thermal ions are described by gyrokinetic equations. Several optimizations are applied to both extended-MHD and PIC components resulting in code speeds much faster than other similar codes. Using this code, we have conducted linear and nonlinear simulations of alpha particle-driven Alfven eigenmodes and associated alpha particle transport with multiple toroidal mode numbers (n=0 to 36) for the parameters of ITER steady-state scenario. Linear simulations show excitation of BAEs with most unstable toroidal mode number n=30 and mode peak near the q_min radius. The calculated growth rates and frequencies are close to those obtained by GTC. Nonlinear simulation results show initial saturation of higher-n modes and nonlinear excitation of lower-n modes due to mode-mode coupling. The simulations also show that the Alfven instability causes significant radial transport of alpha particles, and that the n=0 zonal mode reduces the saturation amplitude of the dominant unstable mode by about 40%, thereby reducing the level of radial transport of alpha particles. More details of results will be presented.

[1] P. Y. Jiang et al.; Phys. Plasmas 31, 073904 (2024); Z. Y. Liu et al.; Phys. Plasmas 31, 073905 (2024)