Investigation of the effects of the radial electric field by electrode biasing in a toroidal plasma

The electrode biasing experiments were carried out on the KT-5C tokamak to investigate the effects of the radial electric field Er on turbulence in a toroidal plasma. It is observed the radial electric field is mainly contributed by the poloidal flow both in Ohmic and in electrode biasing discharges. The changes of Er is led by the changes of poloidal flow, and it is the Reynolds stress driving the poloidal flow in Ohmic discharges in the device, but the Reynolds stress is not so important in the electrode biasing discharges. A modestly enhanced ExB shear layer is formed at the plasma edge by the electrode biasing. In the sheared ExB layer, reductions in the fluctuation amplitude, and the radial correlation length as well as the turbulent particle flux, are observed, Indicating that the turbulence suppression by de-correlation is due to the modestly enhanced ExB shear layer.