Effect of impurity distribution on the stability of neoclassical tearing mode

Abstract The neoclassical tearing mode (NTM) stabilization due to variations in impurity distribution has been observed for the first time. For the 2/1 NTM in the high beta, edge localized mode-free H-mode of HL-2A, the kinetic Rutherford equation, when accounting for the effects of impurity and fast ion profiles on the deuterium ion density profile, yields a qualitatively consistent trend with experimental observations. Specifically, both the simulated island evolution transitioning from growth to shrinkage and the experimentally inferred behavior show a corresponding change in the island growth rate from positive to negative. The results indicate that impurity distribution significantly influences NTM stability. Specifically, the higher the impurity gradient in phase with the electron density gradient at the rational surface where the NTM is located, the lower the ion bootstrap current drive term, which favors NTM stabilization. This result is exciting for International Thermonuclear Experimental Reactor (ITER), as it suggests that during pre-fusion power operation (FPO) 2 activities, the originally separate tasks of NTM suppression and medium- Z impurities injection enhancing radiation may have the potential to produce beneficial coupling effects. This has significant and beneficial implications for ITER FPO activities.