Comparison between Stellarator and Tokamak Divertor Transport

Full text: Divertor concepts presently investigated in stellarators follow the same principle as the poloidal divertor in tokamaks, aiming at similar goals and sharing the same technology. However, significant differences in divertor geometry and magnetic configuration exist between helical and axisymmetric devices, which influence the plasma, neutral and impurity transport in the SOL and consequently the functionality of a divertor. From this point of view, stellarators open a new window for exploring the optimal divertor solutions for magnetic confinement fusion devices on a broader basis. Significant differences have been indeed observed between the poloidal divertor of tokamaks and the island-based divertors in helical devices. Using W7-AS, W7-X, LHD and AUG as examples the paper presents a comparison of the basic divertor function elements in terms of recycling, impurity retention and detachment between axisymmetric and helical devices. Physics interpretation is mainly based on EMC3-EIRENE simulations. EMC3-EIRENE is a 3D edge plasma transport code capable of self-consistently treating plasma, neutral and impurity transport in general SOLs of arbitrary geometry. The EMC3 code was initially developed for W7-AS, currently being routinely used for 3D divertor transport studies at W7-X and LHD. In addition, it has been recently applied to tokamaks like TEXTOR, DIII-D, ASDEX-Upgrade, JET and ITER. (author)