High heat flux tests in support of the 3D computational modelling of melting for the EU-DEMO first wall limiters
The EU-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 first wall otherwise. Since tungsten 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 change. The understanding of this problem has paved the way for a 1D thermal computational modelling in Matlab (TARTIFL&TTE [1]), which has then been improved and extended to 3D geometries within a
Multiphysics environment. Hence, the 3D-TARTIFL&TTE implementation in COMSOL Multiphysics [2].
Although the validation has already started with a few data available in literature described in the companion paper [2], dedicated experiments have been performed in the Garching LArge DIvertor Sample Test Facility (GLADIS) for melting studies. Carried out as a joint activity between EUROfusion and UKAEA, its aim is generating a traceable and controlled experimental database in support of heat transfer studies in solid components undergoing phase change. They are here used in support of the 3D-TARTIFL&TTE validation benchmark.
To broaden the database, three different materials have been chosen, i.e. TZM, tungsten, and AISI-316 grade. The requirements defining the experiments comply with the hypotheses behind 3D-TARTIFL&TTE, for it to be able to reproduce the experimental shots. Therefore, uniform heat flux on the surface is provided by the H neutral beam on the footprint and loading time and heat flux magnitude have been chosen such that only melting is reached. This allows the liquid metal to stay in place once formed. No attempts to reach vaporization have been made, since the vertical position of the target promotes the molten layer sliding under
gravity effects. Measured and modelled results show good agreement during the melting phase. As a stepwise benchmark, validation will be sought also under vaporization events. Future work is focussed on addressing this last point.
[1] M.L.Richiusa et al., Rationale behind EU-DEMO limiter’s plasma-facing component design
under material phase change. IEEE Transaction on Plasma Science.
[2] M.L.Richiusa et al., Advances in material phase change modelling approach for EU-DEMO
limiter’s plasma-facing components. Under review in Fusion Engineering and Design.