Optimizing Thermomechanical Performance of Plasma-Facing-Components for Fusion Applications

The pursuit of sustainable fusion energy has accelerated in recent years with major international efforts such as ITER aiming for first plasma and private companies proposing compact pilot reactors. One of the most pressing challenges in these next-generation systems lies in managing the extreme thermal and mechanical loads on plasma-facing components (PFCs), particularly in the divertor region. Among the most promising divertor configurations is the helium-cooled multiple jet (HEMJ) design, which utilizes distributed helium jets to provide rapid heat removal from the tungsten armor layer typically paired with a copper alloy inner container. While the HEMJ concept is thermally efficient, it introduces substantial thermal stress due to mismatches in the coefficient of thermal expansion (CTE) between constituent materials, most notably between tungsten and copper-based heat sinks like CuCrZr. One proposed alternative suggested by Thomas et al. (2025) is the introduction of an interlayer between the tungsten armor and CCZ container made of reduced activation ferritic/martensitic (RAFM) steel, which acts as a mechanical buffer due to its intermediate CTE. This study investigates the thermomechanical performance of optimized HEMJ divertor geometries both with and without a RAFM interlayer. Using a finite element modeling and optimization framework implemented in ANSYS, we simulate heat transfer and stress responses under realistic operating conditions. The optimized geometries, drawn from the parametrized space proposed by Thomas et al. (2025), include a tungsten armor, CuCrZr heat sink, and optionally, a RAFM steel interlayer. Steady-state conjugate heat transfer simulations are performed
using Fluent coupled to a static structural analysis within Mechanical to evaluate the performance of the divertor based on both thermal and mechanical limits. Simulation results indicate the RAFM interlayer improves thermal performance for the listed boundary conditions and redistributes stress from the CCZ container. The RAFM-optimized RAFM including configuration was the only design point that passed the temperature boundaries within the design criteria while none met the stress criteria. In turn, the small operating temperature of RAFM can possibly limit divertor operation ability at higher heat fluxes especially with the already limited temperatures of CCZ. The design component of an interlayer appears to be necessary to control temperature windows and thermal stresses, but materials with more flexible operating windows should be explored.