Effect of neutral hydrogen on edge impurity behavior in stochastic magnetic field layer of Large Helical Device

Two-dimensional (2-D) distribution of impurity line emissions has been measured with 2-D extreme ultraviolet (EUV) spectroscopy in Large Helical Device (LHD) for studying the edge impurity transport in stochastic magnetic field layer with three-dimensional (3-D) structure. The impurity behavior in the vicinity of two X -points at inboard and outboard sides of the toroidal plasma can be separately examined with the 2-D measurement. As a result, it is found that the carbon location changes from inboard to outboard X-points when the plasma axis is shifted from R _ax = 3.6 m to 3.75 m. A 3-D simulation with EMC3-EIRENE code agrees with the result at R _ax = 3.75 m but disagreed with the result at R _ax = 3.60 m. The discrepancy between the measurement and simulation at R _ax = 3.60 m is considerably reduced when an effect of neutral hydrogen localized in the inboard side is taken into account, which can modify the density gradient and friction force along the magnetic field.