Evolution of tungsten degradation under combined high cycle edge-localized mode and steady-state heat loads

Abstract

Combined thermal shock and steady-state heat loads (SSHLs) can have an impact on divertor materials and are therefore important for lifetime estimations and evaluations of operational thresholds of divertor components in future fusion devices such as ITER. This paper discusses the results of tests performed in the electron beam facility JUDITH 2 (Forschungszentrum Jülich, Germany) on actively cooled tungsten specimens, loaded with edge-localized mode-like thermal shocks (pulse duration 0.48 ms, power densities 0.14–0.55 GW m−2, frequency 25 Hz and up to 1000 000 pulses) either with or without an additional SSHL of 10 MW m−2. The material showed no damage at 0.14 GW m−2 (independent of the SSHL) for up to 250 000 pulses. At a power density of 0.27 GW m−2 (without SSHL), surface roughening occurred at 100 000 pulses, developing into a crack network at 1000 000 pulses. In general, the additional SSHL resulted in an earlier (in terms of pulse number) and more severe material degradation.