(TH/P2-20) Effects of Magnetic Island Induced Symmetry Breaking on Plasma Confinement and Island Evolution in Tokamaks

K.C. Shaing1)
1) University of Wisconsin, Madison, United States of America

Abstract.  Magnetic islands exist in most tokamak discharges. The toroidal symmetry in | B | is broken when an island is embedded in the equilibrium magnetic field B in tokamaks. Plasma confinement properties in the vicinity of an island are different from those in the region away from the island. Physically, this is a result of the modifications on the plasma viscosity in the presence of the island. Interesting plasma confinement properties including, besides the usual particle and energy fluxes, the momentum transport and the bootstrap current, are derived from the island induced plasma viscosity. The consequence of the momentum transport process modifies plasma flow and the radial electric field in the vicinity of an m = 1 island, and provides an explanation for plasma confinement improvement in snakes. Here, m is the poloidal mode number. The additional bootstrap current density induced by the presence of an island modifies the island evolution. It is found that island-induced bootstrap current has stabilizing influence on the island dynamics for m > 1 islands in plasmas with high poloidal beta. Here, poloidal beta is the ratio of plasma pressure to the poloidal magnetic field pressure.

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