The influences of electrode biasing (EB) on toroidal rotation and turbulent (toroidal) momentum transport at the plasma edge have been experimentally studied in the J-TEXT tokamak. In the absence of bias (i.e. the bias current Ib = 0 A), plasma toroidal rotation at the edge of the confined region is intrinsically towards the co-Ip direction (parallel to plasma current); in the presence of bias, edge rotation can be greatly modified, and shows positive correlation with the bias current. As the dominant term in the turbulent momentum flux, the toroidal-radial Reynolds stress term is found to give rise to an intrinsic torque in the experiments. The local momentum balance is provided by a viscous damping-like term on the velocity. Moreover, the existence of intrinsic torque at the edge is directly verified by cancelling out the local rotation under negative bias (Ib ≈ −60 A). The corresponding intrinsic torque density at the plasma edge is about 0.65 N m−2, in the co-Ip direction. Further comparison shows that this intrinsic torque can be reasonably explained by the measured residual stress, providing direct evidence for the hypothesis that the residual stress is the origin of the intrinsic rotation.
The effect of impurity seeding on edge toroidal rotation in the ADITYA-U tokamak