The neoclassical plasma viscosity analyses relevant to high-ion-temperature plasmas in the Large Helical Device (LHD)

High ion-temperature (Ti) hydrogen plasmas, about 5 keV at the density range of 1.2-1.6x1019 m-3, have been successfully realized in the LHD. The toroidal-view charge exchange recombination spectroscopy (CXRS) has observed the fast toroidal rotation velocity (Vt) with a several 10 km/s at the core region in these high-Ti hydrogen plasmas. Previously high-Ti (more than 10 keV) plasmas have also been obtained in high-Z (like Ar, Ne) plasmas in LHD, in which several 10 km/s of toroidal rotation at the core region was also observed. Although, the impact of fats toroidal rotation on confinement improvement of ions is still unclear, consideration how the toroidal viscosity can be lowered at the core region in the LHD to maintain the faster toroidal rotation would be an important research issue. For this purpose, neoclassical transport code, DKES, has been begun to be applied to high-Ti LHD discharges. The present status of this application and a possible future direction is reported. (author)