Global gyrokinetic simulation for toroidal impurity mode turbulence

Abstract

In this study, global gyrokinetic simulations of the toroidal impurity mode (tIM) turbulence are performed. A linear analysis shows that the tIM is an instability that occurs in the bad curvature region when the density gradients of bulk ions and impurities are in opposite directions. The tIM can be unstable even when the temperature profiles are flat. In the presence of temperature gradients, the tIM and toroidal ion temperature gradient (tITG) mode could coexist. For the small temperature gradient, the tIM is found to be dominant. The tIM turbulence drives the large inward impurity and outward ion particle transports. Furthermore, the inward ion heat flux driven by the tIM turbulence causes the ion temperature profile to be more peaked than the initial one. For the large temperature gradient, while such inward ion heat flux does not occur because of the dominant tITG mode, the large inward impurity and outward ion particle fluxes are still observed due to the subdominant tIM. These results indicate that the tIM plays an important role in turbulent heat and particle transport when impurities are injected.