High Heat Flux Tests in Support of the 3-D Computational Modeling of Melting for the EU-DEMO First Wall Limiters

The EU-DEMOnstration fusion power plant (DEMO) first wall protection strategy relies on limiter components to face both normal and off-normal plasma transient events. The heat loads during these events are likely to damage the breeding blanket's first wall otherwise. Since W is the preferred plasma-facing material for EU-DEMO, the plasma-facing component design of the limiters follows considerations based on heat transfer in solids undergoing phase transition. The understanding of this problem has paved the way for a 1-D thermal modeling in MATLAB Thermal Analysis foR Tracking InterFaces under meLting&vaporizaTion-induced plasma Transient Events (TARTIFL&TTE), which has then been improved and extended to 3-D geometries within a Multiphysics environment. Hence, the 3-D TARTIFL&TTE implementation in COMSOL Multiphysics. Although the validation has already started against some data available in the literature and described in the companion paper, dedicated experiments are performed in the Garching LArge DIvertor Sample Test Facility (GLADIS) for melting studies. Carried out as a joint activity between EUROfusion and U.K. Atomic Energy Authority (UKAEA), the aim of these experiments is generating a traceable and controlled experimental database in support of heat transfer studies in solid components undergoing phase transition. The data are here used in support of the 3-D TARTIFL&TTE validation benchmark. To broaden the database, three different materials are chosen, i.e., TZM, W, and SS-316 grade. The requirements defining the experiments comply with the hypotheses behind 3-D TARTIFL&TTE, for it to be able to reproduce the experiments. Therefore, a uniform heat flux on the loaded surface is provided by the H neutral beam on the footprint, and loading time and heat flux magnitude are chosen such that only melting is reached. This allows the liquid metal to stay in place once formed. No attempts to reach vaporization are made, since the vertical position of the target promotes the molten layer sliding under gravity effects. Measured and modeled results (temperature, absorbed energy, and melt layer depth) show good agreement during the melting phase. As a stepwise benchmark, validation will be also sought under vaporization events. Future work is focused on addressing this last point.