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Abstract
Spatially resolved spectra have been measured with visible spectroscopy in Large Helical Device (LHD). Strong line emissions of H I, He I and C III have been observed at a limited area near the inboard-side X-point. Such a poloidally inhomogeneous radiation structure is drastically changed when the radius of the magnetic axis is shifted from Rax = 3.6 m to 3.9 m: another strong emission emerges near the outboard-side X-point. In order to understand the physical mechanism the electron temperature and density are evaluated from intensity ratios of neutral hydrogen and helium lines at poloidal locations near both the X-points and at the bottom O-point edge. It is found that the changes of the electron temperature and density along the poloidal direction are too moderate to explain the inhomogeneity of line emissions for both the configurations. The present result suggests that the poloidal inhomogeneity of neutral emissions arises owing to the inhomogeneous neutral density distribution rather than the difference of the electron density or temperature.
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