Abstract
The W7-X stellarator has so far performed experiments under both limiter and divertor conditions. The plasma is mostly generated by ECR-heating with powers up to 6.5 MW, and the plasma density is usually limited by the radiation losses from low-Z impurities (such as carbon and oxygen) released mainly from the graphite targets. The present work first summarizes the radiation loss fractions f rad achieved in quasi-stationary hydrogen plasmas in both operational phases, and then shows how impurity radiation behaves differently with the two different boundary conditions as the plasma density increases. The divertor operation is emphasized and some beneficial effects (with respect to impurity radiation) are highlighted: (1) intensive radiation is located at the edge (r/a > 0.8) even at high radiation loss fractions, (2) the plasma remains stable up to f rad approaching unity, (3) the reduction in the stored energy is about 10% for high f rad scenarios. Moreover, effects of wall boronisation on impurity radiation profiles are also presented.
Highlights
W7-X is an optimized quasi-isodynamic stellarator [1] with non-planar superconducting coils
The plasma is mostly generated by ECR-heating with powers up to 6.5 MW, and the plasma density is usually limited by the radiation losses from low-Z impurities released mainly from the graphite targets
The present work first summarizes the radiation loss fractions frad achieved in quasi-stationary hydrogen plasmas in both operational phases, and shows how impurity radiation behaves differently with the two different boundary conditions as the plasma density increases
Summary
W7-X is an optimized quasi-isodynamic stellarator [1] with non-planar superconducting coils. Publications on the thermal energy dissipation capability of the island divertor in W7-X have reported that the power incident on the targets can be dissipated by line radiation from low-Z impurities (mainly carbon and oxygen) without relatively strong deterioration of the core plasma performance. These stable high-density, high-radiation regimes (with plasma detachment) were achieved in the divertor operational phases before and after wall boronisation in 2017 (OP1.2a) and 2018 (OP1.2b), respectively [12, 13].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
