Observation of toroidal flow on LHD

In order to investigate the formation of toroidal flow in helical systems, both NBI driven flow and spontaneous toroidal flow are observed in the Large Helical Device (LHD). The toroidal flow driven by NBI is dominant in the plasma core while the contribution of the NBI driven toroidal flow is small near the plasma edge. The spontaneous toroidal flow changes its direction from co to counter when the radial electric field is changed from negative to positive at the plasma edge. The direction of the spontaneous toroidal flow due to the radial electric field near the plasma edge is observed to be opposite to that in the plasma core where the helical ripple is small. (author)