Parametric design study of a substrate material for a DEMO sacrificial limiter

Towards the realization of nuclear fusion, a future reactor must provide efficient and safe power exhaust through both the divertor and FW. Recent studies suggest that the greatest engineering challenges of plasma-facing components (PFCs) may arise from the occurrence of plasma transients, when extreme heat fluxes are expected. In severe cases, extensive surface vaporization, melting and re-solidification may lead to excessive degradation of conventional PFCs. An eventual failure would compromise the reactor safety as well as its prompt return to normal operation. A sacrificial limiter provided with a micro-engineered substrate material is being investigated for DEMO to cope with the harsh conditions occurring during unmitigated plasma disruptions. Among the possible solutions, innovative materials such as tungsten (W) based lattice structures can be tailored to meet functional requirements and prevent severe failures. As a further step in this direction, an equivalent solid model, originally developed and validated for open-cell Al foams, was transferred to W foams and the scaling law of its thermo-physical properties evaluated as a function of the most influential parameters. In the present work, a design optimization tool for the thermal behavior of the substrate material is presented. The latter is modeled as a homogeneous material having equivalent properties. A parametric design study was carried out to assess their impact on the global behavior of the PFC. Independent combinations of equivalent thermal conductivity and density have been applied to the substrate material by scaling the corresponding properties of bulk W. For each design point, results were tabulated and compared with user-defined operating requirements. Afterwards, a post-processing routine was implemented for effective visualization of the space of solutions. Ultimately, tailored lattice structures potentially able to fulfill the operating requirements are proposed. An existing solid model for open-cell W foams was employed to design the features of such material based on the results of the parametric study.