The influence of electrode biasing on plasma confinement in the J-TEXT tokamak

Abstract

The influence of both positive and negative bias on global and plasma-edge parameters has been comparatively studied with a newly designed electrode biasing system in the J-TEXT tokamak. Compared to the 0 V bias case, the global particle confinement of plasma is enhanced under bias with both polarities, with the increments of the central line-averaged density and the soft x-ray emission, as well as the reduction of the edge Hα radiation level. The suppression of plasma-edge fluctuations and turbulent particle transport are obviously observed under bias, in different degrees with different polarities. The potential fluctuation amplitude is observed to be increased at the vicinity of the limiter under positive bias, with the existence of a peaked low-frequency mode characterized as high coherence and near-zero cross-phase poloidally in the edge region, which is not found in the negative bias case. The poloidal correlation length of turbulence is greatly enhanced under bias with both polarities; it shows a positive correlation with the amplitude of the poloidal phase velocity, which is mainly driven by the local Jr × B torque at the plasma edge under bias. The characteristic parameters of intermittent events (i.e. blobs), including amplitude, radial velocity, related particle flux and radial size, decreased dramatically under bias in the edge region.