Intrinsic toroidal rotation in tokamaks from global total-f gyrokinetic simulations

Understanding intrinsic toroidal rotation is important for future tokamaks like ITER. In gyrokinetic plasmas, the ion gyrocenter toroidal angular momentum can be transported in the radial direction via three processes: turbulent transport of the parallel momentum, neoclassical transport of the parallel momentum, and turbulent transport of the E cross B momentum. Theories and conventional delta-f simulations have been mainly focused on the first process based on the ordering assumption. However, global total-f simulations have suggested that the three processes could be on the same order. Here, we study intrinsic toroidal rotation in flux-driven ion-temperature-gradient turbulence using the global total-f gyrokinetic code XGC1. After the turbulence onset, zonal flows quickly form and reach a steady value. Meanwhile, there is a persistent toroidal-rotation acceleration, whose direction correlates with the zonal-flow pattern. Simulation results showed that for the ion gyrocenter particle flux, the turbulent contribution is balanced by the neoclassical contribution, resulting in steady-state zonal flows. However, for the momentum flux, simulations suggested that the turbulent transport of E cross B momentum is not balanced by other processes and results in persistent toroidal-rotation acceleration. The correlation between zonal flows and toroidal rotation can be explained as the result of the correlation between turbulent particle and momentum flux.