Role of Reynolds stress-induced poloidal flow in triggering the transitionto improved ohmic confinement on the HT-6M Tokamak

Time and space resolved measurements of electrostatic Reynolds stress, radi al electric field E-r, and plasma rotations have been performed across the transition to improved Ohmic confinement in the Hefei Tokamak-GM (HT-6M). T he first experimental evidence of the correlation between the enhanced Reyn olds stress gradient and the poloidal flow acceleration in the edge plasma is presented. The results indicate that the turbulence-induced Reynolds str ess might be the dominant mechanism to create the sheared poloidal flow and E-r, which may further trigger the transition.