Impurity seeding for radiative power exhaust in the W7-X island divertor

The impact of intrinsic and actively injected impurities on plasma edge conditions is crucial for optimizing fusion devices like Wendelstein 7-X. The 3D magnetic structure of the scrape-off layer (SOL) plays an essential role in determining the effect of impurities on the plasma edge. It is significant to align active gas injection with the island divertor geometry to improve effectiveness, as injected gases can manipulate neutral fueling behavior and steer heat flux, thereby facilitating improved fueling in fusion devices.

Numerical analysis with EMC3-EIRENE and experiments were employed to investigate the impact of radiative edge cooling by impurities on transport in the plasma SOL and at the core-edge interface. Injection of nitrogen and neon in the plasma edge caused a reduction in edge temperature and enhanced radiation, with nitrogen demonstrating a faster response compared to neon. Initial experiments with island divertors highlighted the importance of gas injection location with respect to the island geometry, a finding confirmed by simulations. [F. Effenberg et al 2019 Nucl. Fusion 59 106020DOI 10.1088/1741-4326/ab32c4]