Intrinsic Toroidal Rotation Driven by Turbulent and Neoclassical Processes in Tokamak Plasmas from Global Gyrokinetic Simulations

Gyrokinetic tokamak plasmas can exhibit intrinsic toroidal rotation driven bythe residual stress. While most studies have attributed the residual stress tothe parallel-momentum flux from the turbulentE×B motion, the parallel-momentum flux fromthe drift-orbit motion (denoted Π_∥^D) and theE×B-momentum flux from theE×B motion (denoted Π_E× B) areoften neglected. Here, we use the global total-f gyrokinetic code XGC tostudy the residual stress in the core and the edge of a DIII-D H-mode plasma.Numerical results show that both Π_∥^D and Π_E× B makeup a significant portion of the residual stress. In particular,Π_∥^D in the core is higher than the collisional neoclassical levelin the presence of turbulence, while in the edge it represents an outflux ofcounter-current momentum even without turbulence. Using a recently developed“orbit-flux” formulation, we show that the higher-than-neoclassical-levelΠ_∥^D in the core is driven by turbulence, while the outflux ofcounter-current momentum from the edge is mainly due to collisional ion orbitloss. These results suggest that Π_∥^D and Π_E× B can beimportant for the study of intrinsic toroidal rotation.