Improvement of neoclassical ion thermal transport near the plasma edge in the electron root regime on LHD

Positive radial electric field, Er, was observed at the edge region in the low-density NBI plasmas of the Large Helical Device (LHD). Ion thermal diffusivities, χi, are evaluated by the local transport analysis for two different density plasmas and for two cases of the magnetic axis position. In the standard configuration case, χi was reduced by large positive Er, while no reduction in χi was found in the inward shifted case.A certain level of suppression of the neoclassical ripple transport by Er seems to be confirmed since the neoclassical transport is considered to be more dominant in the standard magnetic configuration plasmas.