Thermal mechanical evaluation of candidate tokamak divertor elements informing fusion materials design windows

Materials innovations represent a critical need for future fusion pilot plants. Plasma facing components (PFCs) used in the divertor will require materials to operate continuously under harsh conditions involving high heat loads and particle fluxes that act to damage their surface while simultaneously degrading their bulk properties. In this study, a framework is presented to evaluate candidate fusion materials operating windows using finite element (FE) simulations for thermomechanical performance modeling of two divertor designs – the pipe monoblock and helium cooling by multiple jets (HEMJ) architectures – with the maximum achievable surface heat fluxes mapped for each design within associated materials constraints. The pipe monoblock failed to accommodate a 10 MW/m² incident heat flux while maintaining the materials within their design specifications. The HEMJ narrowly met this target, but only under optimistic assumptions about material properties and steady-state heating conditions. For example, maintaining the temperature of all three materials within their respective operating windows required the HEMJ coolant temperature to be held between 155 and 160 °C at a flow rate of 13.5 g/s. Critical performance-limiting materials characteristics were identified from these simulations and included the upper temperature of the copper alloy heat sink, narrow operating temperature range and low thermal conductivity of the steel interlayer, and eventual closing of the tungsten operating window due to neutron irradiation. Based on these observations, materials innovations are outlined for expanding the operating windows under conditions that consider the evolution of materials properties due to the fusion environment as well as transient heat flux excursions.