Impurity Retention Effect in the Edge Ergodic Layer of the Large Helical Device

The impurity transport characteristics in the ergodic layer of the Large Helical Device (LHD) are analyzed using the 3D edge transport code (EMC3-EIRENE), in comparison with the experimental data. The 3D modeling predicts the impurity retention (screening) in the ergodic layer at the high-density plasma. It is found that the edge surface layer plays an important role in impurity retention, where the friction force significantly dominates over the thermal force. The line intensity measurements of CIII to CVI show consistent behavior with the modeling, indicating impurity retention in the ergodic layer. The applicability of the model for high-Z impurity is also discussed, and it is found that the experimental data is consistent with the results of edge transport modeling.