Within EUROfusion activities towards a conceptual design for a Helical Axis Advanced Stellarator (HELIAS) demonstration reactor, CIEMAT is developing a decoupled First Wall (FW) concept. The proposed approach makes use of a liquid metal (LM) as the plasma-facing material (PFM) and decouples the FW from the breeding blanket (BB), aiming to reduce scheduled interventions on blanket segments and to limit frequent remote handling to smaller, replaceable FW panels. The decoupled FW relies on Capillary Porous System (CPS) technology, using lithium as PFM. This work presents two FW design alternatives, focusing on component integration and cooling schemes. To evaluate technological feasibility, numerical models have been developed, including a 3D parametric analysis of key thermo-hydraulic parameters and a structural assessment of the decoupled system. In parallel, preliminary studies on capillarity behavior, from both theoretical and numerical perspectives, are used to define early operating constraints for stable lithium supply and retention. Additionally, initial concepts for coolant routing and pipe integration are also presented, supporting further engineering development of the decoupled FW for HELIAS.
Nogueron et al. (2026) studied this question.