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.