Understanding island divertor physics for Infinity Two Power Plant

Successful operation of fusion power plant (FPP) depends on a particle and power exhaust strategy which simultaneously facilitates good core performance. “Infinity Two” (INF2) is Type One Energy’s proposed design for a practical FPP with a robust baseline physics solution [1]. INF2 is planned to use island divertor (ID) exhaust concept [2] wherein the open field lines inside the islands guide the particles and the energy towards the targets [3]. To evaluate the different divertor designs in INF2 for best performance in terms of divertor heat and particle fluxes, neutral pressure in the divertor, neutral compression, radiation fraction and good core performance [4], a good analytical understanding of IDs is necessary, especially concerning heat flux width (λ_q) estimation and plasma detachment physics. A summary based on an extensive literature survey (both theoretical and experimental results) from stellarators: W7-X, W7-AS, LHD, TJ-II and other tokamaks is provided, and the analysis has been scaled to stellarator power plant. An analytical reasoning has been developed to answer critical questions about optimum island width size, λ_q , connection length etc. for a superior core-edge performance in detached scenarios in INF2.

[1] C. C. Hegna, et al. Journal of Plasma Physics 91.3 (2025): E76

[2] A. Bader, et al. Journal of Plasma Physics 91.2 (2025): E67

[3] F. Sardei et al. Contributions to Plasma Physics 40.3-4 (2000), pp. 238–250

[4] O. Schmitz et al. Nuclear Fusion 61.1 (2020): 016026