Three-dimensional neutral particle transport simulation for analyzing polarization resolved H-alpha spectra in the large helical device

Change of Hα intensity profiles depending on magnetic configurations is observed in the divertor plasma. It can be explained by the magnetic field line structures in the ergodic layer and the divertor legs. The behavior of neutral particles in the plasma periphery is investigated by a three-dimensional neutral particle transport simulation code which assumes that the distribution of the plasma flow onto the divertor plates corresponds to that of the strike points calculated by magnetic field line traces. Vertical Hα intensity profiles and polarization resolved Hα spectra are calculated by the simulation code including the effect of Doppler broadening, fine structure splitting and polarization of the Hα emission, which agree well with the measurements in various magnetic configurations. It shows spontaneous formation of high neutral density in inboard side of the torus, which is independent of the magnetic configurations in LHD.