Evaluation of poloidal distribution from edge impurity emissions measured at different toroidal positions in Large Helical Device

Two-dimensional (2-D) distribution of edge impurity line emissions has been measured for CIV, CVI, FeXV and FeXVIII using a space-resolved extreme ultraviolet (EUV) spectrometer in Large Helical Device (LHD). The top and the bottom edges of the distribution show a strong emission trajectory along the plasma boundary. In this study, the poloidal distribution of the impurity emissivity is evaluated by analyzing the 2-D distribution against magnetic flux surfaces calculated with a three-dimensional (3-D) equilibrium code, i.e., VMEC. The inner and outer boundaries of the edge impurity locations are estimated by analyzing the vertical profile of each impurity emission measured at different toroidal positions. The observation chord length passing through an emission contour is calculated on the basis of the radial thickness of the impurity emission location. The poloidal distributions of CIV, CVI, FeXV and FeXVIII with different ionization energies are thus reconstructed from their 2-D distributions. A non-uniform poloidal distribution is clearly observed for each of these impurity species at different plasma radii. It is experimentally confirmed that the poloidal distribution becomes gradually uniform as the radial location of the impurity ions changes from the ergodic layer toward the plasma core. The non-uniform poloidal distribution of the CIV emissivity is further confirmed by a simulation with the 3-D edge transport code, EMC3-EIRENE. (author)