Gyro-Landau-fluid simulations of impurity effects on ion temperature gradient driven turbulence transport

Abstract The impurity effects on ion temperature gradient (ITG) driven turbulence transport in tokamak core plasmas are investigated numerically via global simulations of microturbulence with carbon impurities and adiabatic electrons using extended fluid code (ExFC) based on a four-field gyro-Landau-fluid (GLF) model. The multispecies form of the normalized GLF equations guaranteeing self-consistent evolution of both bulk ions and impurities is presented. With parametric profiles of the cyclone base case (CBC), well-benchmarked ExFC is employed to perform simulations focusing on different impurity density profiles. For fixed temperature profile, it is found that the turbulent heat diffusivity of bulk ions in quasi-steady state is usually lower than that without impurity, which is contrary to the linear and quasi-linear predictions. The evolutions of the temperature gradient and heat diffusivity exhibit a fast relaxation process, indicating that the destabilization of the outwardly peaked impurity profile is a transient state response. Furthermore, the impurity effects of different profiles can obviously influence the nonlinear critical temperature gradient, which are likely to be dominated by linear effects. These results may evidence the plasma confinement improvement by the impurities probably through adjusting both heat diffusivity and critical temperature gradient.