Experiments and modelling on ASDEX Upgrade and WEST in support of tool development for tokamak reactor armour melting assessments

Abstract

The risk of metallic armour melting constitutes a major concern for ITER and DEMO. Combined computational and experimental effort has led to a successful understanding of melt dynamics in present-day tokamaks, but there remain unexplored melting regimes of relevance to future reactors. Analysis of recent poor-versus-efficient thermionic emitter sample exposures in ASDEX-Upgrade and ITER-like actively cooled tungsten leading edge exposures in WEST is presented. The coupled thermal response and melt dynamics is modelled with the new MEMENTO code employing the MEMOS-U physics model which has no adjustable parameters. In the weak Lorentz force regime accessed in the exposures, very close agreement between modelling and experiments is achieved not only for the deformation profiles, but also for the additional, unique to these experiments, constraints; simultaneous thermal response of two different materials in ASDEX-Upgrade and in-situ detection of melt build-up in WEST. • Two new melt experiments in ASDEX-Upgrade and WEST have accessed previously unexplored regimes. • The impact of thermionic emission in the energy and momentum balance of tungsten melting events is assessed. • Typically inaccessible in previous experiments secondary thermo-capillary effects are unmasked. • The coupled thermal response and melt dynamics is modelled with the new 5MF code employing the MEMOS-U physics model. • Enhanced value of the model validation effort due to existence of novel, unique to these experiments, constraints.