Gyrokinetic simulation of electromagnetic instabilities in CFETR steady-state scenario

This study performs linear electromagnetic simulations with the gyrokinetic code NLT to examine the dominant instabilities across different radial positions in the CFETR steady-state scenario featuring internal transport barrier (ITB). The simulations reveal that in the plasma core region, the kinetic ballooning mode (KBM) dominates and exhibits strong sensitivity to both ion temperature gradient and plasma pressure ratio. As the radial position increases, the dominant instabilities gradually transit from KBM to ion temperature gradient (ITG) mode and trapped electron mode (TEM). The effects of fast deuterium ions and impurities on the electromagnetic instabilities are further researched. It is found that both fast deuterium ions and argon impurities markedly suppress KBM. The stabilization mechanism of fast deuterium ions depends on the temperature of fast deuterium ions. The kinetic effects remain significant at low temperature, whereas the stabilization mechanism is primarily dominated by dilution effects at high temperature. In contrast, in addition to the dilution effects, the effects of argon density gradient also play a crucial role in KBM stability. For the ITG mode in the outer region of ITB, the influence of fast deuterium ions is limited due to the low charge concentration, whereas argon impurities exert a much stronger stabilizing effects, consistent with the combined mechanism in KBM that involves dilution and density gradient effects.