Poloidal Rotation In Tftr Reversed Shear Plasmas

A bifurcation in the core poloidal rotation of carbon impurity ions in the Tokamak Fusion Test Reactor (TFTR) has been observed prior to the transport bifurcation associated with enhanced reverse shear plasmas. In a narrow radial region of the plasma, the impurity ion poloidal rotation reverses direction. This poloidal flow is associated with the establishment of a large negative radial electric field with strong shear. The measured poloidal velocities before, during, and after this precursor differ from neoclassical predictions.