Neoclassical and turbulence-driven ExB flow and macroscopic current structures in magnetic island

Global gyrokinetic simulations with self-consistent coupling of neoclassical and turbulent effects show turbulence can significantly reduce plasma self-driven current generation in collisionless regime, generate current profile corrugation near rational magnetic surface and nonlocally drive current in the linearly stable region - all these are expected to have broad impact on tokamak confinement and global stability. The magnetic island is found to strongly change ExB shear flow and self-driven current structures in the island region. A charge separation due to electron parallel transport induced finite electron density flattening in the O-point generates a strong radially localized ExB shear layer, which may facilitate the formation of a transport barrier near the resonant magnetic surface by decoupling plasma inside the shear layer from the outside. On the other hand, turbulence self-generated zonal flow shows a helical structure akin to the island in large island case, namely, a poloidal ExB shear flow on the perturbed magnetic surface, which may prevent the turbulence developed in the outside of the island from spreading into the O-point. The parallel mean current is also largely modified in the island region by both neoclassical and turbulent effects.

Work supported by U.S. DOE Contract DE-AC02-09-CH11466 and SciDAC Tokamak Disruption Simulation project.