Observations of spontaneous toroidal flow on LHD

Spontaneous toroidal flows driven by radial electric field and ion temperature gradient are studied in the Large Helical Device (LHD). The positive radial electric field drives spontaneous flow in the counter direction at the plasma edge and in the co-direction near the magnetic axis. The difference in the direction of spontaneous flow between the core and the edge is considered to be due to the difference in a ratio of the helical ripple to the toroidal ripple. Ion temperature gradient causes the spontaneous toroidal flow is clearly observed and becomes one of a dominant component of the toroidal flows in the high ion temperature discharges in LHD. (author)