TH-C/P8-44 Interaction between Turbulence and Neoclassical Dynamics and Its Effect on Tokamak Transport: Gyrokinetic Simulations and Theory

Abstract. The relationship between momentum and energy transport is investigated with focus on understanding recent experimental observations, using global gyrokinetic simulations with proper coupling between turbulence and neoclassical dynamics. First, a large inward flux of toroidal momentum is found robustly in the post saturation phase of ion temperature gradient (ITG) turbulence. As a consequence, core plasma rotation spins up. The underlying physics for the inward flux is identified to be the generation of residual stress due to the k‖ symmetry breaking induced by self-generated zonal flow shear which is rather stationary in global simulations. Our neoclassical simulations have observed an enhancement of neoclassical momentum transport in steep rotation gradient regions and a significant inward nondiffusive momentum flux driven by ion temperature gradients. However, the overall neoclassical contribution to the toroidal momentum transport is negligibly small. It is found that residual turbulence can survive the dissipation of a strong mean E×B flow shear and drive a significant momentum flux. Moreover, the equilibrium E×B flow shear is found to reduce the turbulence driven transport for energy more efficiently than for momentum. These findings may offer one explanation for recent puzzling experimental observations that the toroidal momentum transport remains highly anomalous, even while the ion heat flux is reduced to a neoclassical level.