Vertical profiles and radial locations of He II and C IV line emissions observed at different toroidal angles in LHD

Vertical profiles of edge impurity line emissions of He II and C IV have been measured at different toroidal locations of Large Helical Device (LHD) by scanning horizontally a space-resolved EUV spectrometer in order to observe the edge distribution at different poloidal locations. Radial location of He II with ionization energy of E_i = 54.4 eV reflects the penetration depth of neutral helium and radial location of C IV with E_i = 64.5 eV expresses the index of plasma edge boundary in ergodic layer of LHD. The result indicates that the radial position of He II is located at inner side than that of C IV, whereas the ionization energy of He II is smaller than that of C IV. It is found that the radial position of He II estimated from the C IV position has a nearly constant distance of 4 mm from the plasma edge against different poloidal locations including region near X-points. The distance is in a good agreement with analysis assumed neutral helium influx with room temperature (300 K). It suggests that the neutral helium mainly enter the plasma as background gas in the vacuum vessel, but not as recycling particle. (author)