Speaker
Description
The development of a viable plasma exhaust solution is one of the principal challenges on the path towards stellarator fusion reactors. While the island divertor of Wendelstein 7-X (W7-X) has demonstrated excellent performance in terms of detachment and steady-state operation, its present open geometry limits neutral compression and particle exhaust. A closed divertor configuration is therefore being investigated as a promising route towards enhanced density buildup, improved impurity retention, and increased radiative power dissipation.
In this work, we present the physics basis and numerical assessment of closed island divertor concepts for W7-X. The study is performed primarily with the EMC3-EIRENE code, a three-dimensional mean-field plasma-neutral transport solver, to investigate the influence of divertor closure on plasma and neutral dynamics. Guided by simplified heat transport modelling and realistic engineering constraints, a range of closed divertor geometries is explored. The simulations demonstrate promising trends, including enhanced downstream density buildup and favourable localization of plasma-neutral interactions, while maintaining acceptable heat loads on the divertor targets. The underlying physical mechanisms governing these improvements are identified and discussed.
Building on this understanding, we present simulations of a tungsten closed divertor configuration with impurity seeding to assess its exhaust performance under reactor-relevant conditions. These results provide important insight into the potential of closed island divertors and establish a physics-based foundation for future divertor upgrades and experimental implementation on W7-X.