Role of Radial Electric Field Shear at the Magnetic Island in the Transport of Plasmas

The structures of radial electric field and transport at the magnetic island are investigated using n/m=1/1 external perturbation coils in the Large Helical Device (LHD). The radial profiles of plasma potential, as well as the electron temperature and density, shows flattening inside the magnetic island and the large shear of the radial electric field is observed at the boundary of the magnetic island. When the current of n/m=1/1 external perturbation coils becomes large enough, the finite radial electric field appears inside the magnetic island. The abrupt appearance of plasma flow inside the magnetic island suggests the non-linearity of the viscous force at the boundary of the magnetic island. The thermal diffusivity perpendicular to the magnetic filed inside the magnetic island is estimated with the cold pulse propagation, which is produced by a tracer-encapsulated solid pellet (TESPEL). The time delay and amplitude of the electron temperature of the cold pulse show much lower thermal diffusivity inside the magnetic island (0.16 m2ls; than that outside the magnetic island (2 m2ls;, which is a clear evidence for the significant reduction of heat transport inside the magnetic island