In this paper, a comprehensive comparison of particle transport and exhaust features of the island divertor at the HSX experiment at UW Madison and the Wendelstein 7-X (W7-X) stellarator in Greifswald, Germany is presented. It is shown that the magnetic island geometry which is the topological basis for this divertor concept defines the fueling and exhaust ratio for recycled neutral particles sources at the surrounding vessel walls and divertor targets. While HSX does not feature a formal divertor baffling structure it still enabled to reveal the neutral compression capability in the island domain, which would allow defining a physical divertor structure for particle exhaust. At W7-X, at the time of the experiments, no divertor structure was implemented either and the experiments discussed in the paper were an important step to explore the role of the islands for the plasma edge transport. Presently, the first campaign with the island divertor including a full divertor housing and closure is commencing and the study presented in this paper provided substantial insight into the relation between the particle transport caused by the islands.
This work is funded by the U.S Department of Energy under grant DE-SC0014210 for collaborative research on large-scale stellarator devices and the HSX grant DE-FG02-93ER54222.
— News: 05-31-2018