Benchmark of kinetic-magnetohydrodynamic hybrid simulation of ion-temperature-gradient instabilities and zonal flow damping

A kinetic-magnetohydrodynamic (MHD) hybrid simulation where gyrokinetic particle-in-cell (PIC) simulation is applied to thermal ions and energetic particles has been developed [1]. In this simulation, the density, parallel momentum, parallel pressure, and perpendicular pressure of thermal ions and energetic particles are calculated by PIC simulation. The electron density is given by the quasi-neutrality condition. The electron pressure is given as the product of the electron density and the equilibrium electron temperature. The time evolution of the perpendicular MHD velocity field is calculated using the MHD momentum equation coupled with the currents of thermal ions and energetic particles. The perpendicular electric field is given by Ohm's law, but the parallel electric field is determined by the electron pressure gradient. In this study, we conducted kinetic-MHD hybrid simulations of ion temperature gradient (ITG) instabilities and zonal flow damping in tokamak plasmas and compared the results with those of the gyrokinetic code GT5D [2]. The results for the linear growth rate of ITG instabilities were in agreement within a range of about 10%. On the other hand, for the frequency of ITG modes, good agreement was obtained for k_θρ_ti ≤ 0.3, but for k_θρ_ti ~0.5, the frequency in the kinetic-MHD hybrid simulation was higher by about 40%. For zonal flow damping, good agreement was observed for both frequency and damping rate.

[1] Y. Todo et al., PPCF 63, 075018 (2021).

[2] Y. Asahi et al., PoP 24, 102515 (2017).