Speaker
Description
The most mature stellarator divertor concept is the island divertor (such as used by Wendelstein 7-X [1]), in which a spatially large magnetic island chain diverts exhausted plasma onto plasma-facing components (PFCs). Despite its maturity, there remain fundamental open questions about how island properties affects edge transport and divertor performance, and how this understanding can be integrated into stellarator design [2, 3, 4]. This work addresses two aspects of island divertor optimisation: (1) the physics determining the properties of island chains in optimised stellarators (for example, the island size and phase, and how this varies as the equilibrium changes) and (2) coil optimisation schemes to target properties of the island chain.
We first present theory relating the properties of the magnetic field to O- and X-points of island chains, using Wendelstein 7-X as a paradigmatic example. We also present fast, user-friendly computational methods to allow automated topological analysis of stellarator magnetic fields. The second part of the talk applies these insights to stellarator coil optimisation schemes. We present a proof-of-principle scheme to design modular coils for an optimised stellarator equilibrium of the “SQuID” variety [5], showing how edge island structures can be explicitly targeted. Implications for plasma-facing component and integrated stellarator power plant design are discussed.
References
[1] Renner, Hermann, et al. "Physical aspects and design of the Wendelstein 7-X divertor." Fusion science and technology 46.2 (2004): 318-326.
[2] Feng, Y. "Up-scaling the island divertor along the W7-stellarator line." Journal of Nuclear Materials 438 (2013): S497-S500.
[3] Lion, J., et al. "Stellaris: A high-field quasi-isodynamic stellarator for a prototypical fusion power plant." Fusion Engineering and Design 214 (2025): 114868.
[4] Davies, R., et al. "Stellarator divertor optimisation for a Stable Quasi-Isodynamic Design (SQuID): magnetic topology, divertor plates and baffle design." 51st EPS Conference on Plasma Physics. European Physical Society, 2025.
[5] Goodman, Alan G., et al. "Quasi-isodynamic stellarators with low turbulence as fusion reactor candidates." PRX Energy 3.2 (2024): 023010