Model prediction of impurity retention in stochastic magnetic boundary and comparison with edge carbon emission in LHD

Impurity retention (screening) potential in the edge region with stochastic magnetic field in LHD (large helical device) is studied numerically using the three-dimensional edge transport code, EMC3-EIRENE, and experimentally applying VUV and EUV spectrometers. The code predicts an impurity retention regime at high densities, where the friction force dominates over the thermal force. The carbon radiation intensities from each charge state are measured in experiments, and compared with the modelling results. The density dependencies of the calculated and measured radiation intensities agree well with each other, confirming the impurity retention in the edge region of LHD. Geometrical advantages of the stochastic field line structure in this concern are also discussed.