Gyrokinetic simulation of turbulence and neoclassical transport for tokamak plasmas with impurity particles

Abstract

Flux-driven full-f gyrokinetic simulations has been performed to study carbon impurity effects on ion temperature gradient (ITG) turbulence and ion thermal ltransport. Employing a gyrokinetic code XGC1 for self-consistent simulation, both main ions and impurities have been evolved self-consistently including turbulence and neoclassical physics. It has been found that carbon impurities self-organize to form an inwardly peaked density profile, which stabilizes ITG instabilities and reduces overeall fluctuations and ion thermal transport. It has also been found that stronger reductions appear in the low frequency components of the fluctuations. Along with the fluctuation change, global structures of radial electric field also change, and this results in the reduction of global avalanche like transport events in the impure plasma. Detailed properities of impurity transport have also been investigated, which revealed that both inward neoclassical pinch and outward turbulent transport are equally important in the formation of the steady state impurity profile. In order to save computing time or to fit the simulation size into a limited computing hardware in a gyrokinetic turbulence simulation of a tokamak plasma, a toroidal wedge simulation may be utilized in which only a partial toroidal section is modeled with a periodic boundary condition in the toroidal direction. The most severe restriction in the wedge simulation is expected to be in the longest wavelength turbulence, i.e., ion temperature gradient (ITG) driven turbulence. The global full-f gyrokinetic code XGC1 is used to study how the transport and turbulence properties change in a toroidal wedge simulation compared to the full torus simulation in an ITG unstable plasma.