Gyrokinetic XGC1 Simulation Study of Magnetic Island Effects on Neoclassical and Turbulence Physics in a KSTAR Plasma

Full text: We perform gyrokinetic simulations to study the effects of a stationary magnetic island on neoclassical and turbulence physics. A KSTAR L-plasma condition is employed for the simulations. Through the simulations, we aim to understand the underlying physical mechanisms of poloidal flows and fluctuations around a stationary (2, 1) magnetic island, which were observed in a recent KSTAR experiment using 2D ECEI diagnostics. From the simulations, it is found that the magnetic island can significantly enhance the equilibrium E x B flow. The corresponding flow shearing is strong enough to suppress a substantial portion of ambient microinstabilities, particularly ∇T_e-driven trapped electron modes. This implies that the enhanced E x B flow can sustain a quasi-internal transport barrier for T_e in an inner region neighbouring the magnetic island. The enhanced E x B flow has a (2, 1) mode structure, which shows a finite phase difference with the mode structure of the magnetic island. It is shown that the flow shear and fluctuation suppression patterns the simulations imply are consistent with the ECEI observations on the KSTAR experiment. (author)