Speaker
Description
Stellarators are a promising candidate for steady-state fusion power plants, and recent achievements on Wendelstein 7-X (W7-X) have further strengthened this prospect. A key determinant of reactor viability is the performance of the divertor, which governs impurity control and particle exhaust. While W7-X has demonstrated excellent heat-flux mitigation and steady-state capabilities, it has not yet achieved one of the central divertor performance metrics: robust particle exhaust enabled by strong divertor density build-up. Present-day stellarator island divertors typically show significantly weaker density build-up compared to tokamak divertors, limiting their ability to operate in regimes with efficient neutral compression and stable exhaust.
Previous modeling has shown that improved density build-up can be achieved in closed island divertors. However, while this behavior has been demonstrated experimentally in open tokamak divertor geometries, comparable density enhancement has not yet been achieved in open stellarator island divertors. Nevertheless, the stellarator 2-point model predicts that, under suitable conditions, similar performance should be attainable in stellarator open divertors. Demonstrating enhanced density build-up in the open island divertor is therefore crucial both for validating the stellarator reactor concept and for guiding the design of future optimized devices.
In this work, we investigate plasma pressure conservation and the resulting divertor density build-up using EMC3-EIRENE simulations of a next-generation stellarator experiment. Parameter scans are performed spanning W7-X–like to reactor-relevant regimes, systematically varying the heating power and cross-field transport coefficients. Our results identify clear operational boundaries at which enhanced pressure conservation along magnetic field lines—from upstream to downstream—emerges, enabling substantially improved divertor density build-up. The mechanism responsible for this transition is analyzed, along with its implications for achieving reactor-relevant particle exhaust in stellarators.
This study provides quantitative guidance for the design of a new stellarator experiment featuring higher heating power and reduced cross-field transport, capable of experimentally demonstrating improved density build-up in an open island divertor. Realizing such performance would represent a critical step toward establishing the stellarator as a competitive pathway to a fusion reactor.