Neoclassical Transport Properties in High-Ion-Temperature Hydrogen Plasmas in the Large Helical Device (LHD)

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High ion temperature (Ti) hydrogen plasmas were successfully demonstrated in the LHD in an experimental campaign (FY2006). The power increase of the perpendicular neutral beam injections (NBIs) has mainly contributed to this achievement. Ti exceeded 5 keV at the average plasma density (ne) of 1.2 × 1019 m-3 and also achieved 3 keV at ne > 3 × 1019 m-3. Neoclassical (NC) analysis was performed for such plasmas. We confirmed that even if Ti or the plasma density became higher, NC transport was remained to a certain value because of the existence of the ambipolar radial electric field (Er), which was roughly two orders of magnitude smaller for cases not involving the existence of ambipolar Er. Besides, a Ti and ne scan of discharge 75235 was also performed to consider the plasma parameter dependence of NC transport. Using these calculations, it is shown that NC ion thermal diffusivities are reduced to a small percentage of NC electron thermal diffusivites even at the fusion reactor relevant parameters such as ne ∼ 1 × 1020 m-3 and Ti ∼ Te ∼ 10 keV.
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