Fusion Science and Technology / Volume 58 / Number 1 / July 2010 / Pages 103-112
Chapter 3. Confinement and Transport / Special Issue on Large Helical Device (LHD)
Spontaneous toroidal flow driven by ion temperature gradient and extreme hollow profile of carbon impurity (denoted as an "impurity hole") is observed associated with the increase of ion temperature gradient in the large helical device (LHD). Spontaneous toroidal flows driven by radial electric field and ion temperature gradient are studied. The positive radial electric field drives spontaneous flow in the counterdirection at the plasma edge and in the codirection near the magnetic axis. The component of the spontaneous toroidal flow driven by ion temperature gradient is clearly observed and expected to be one of the dominant components of toroidal flows in the high-ion temperature discharges in LHD. The transport analysis of the carbon impurity in the discharge with impurity hole reveals a low diffusion coefficient and the outward convection velocity, whereas the inward convection is predicted by the neoclassical theory at half the minor radius.