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Polycrystalline tungsten samples were characterized and exposed to a pure H beam or mixed H/He beam containing 6% He in GLADIS at a surface temperature of 600 °C, 1000 °C, or 1500 °C. After 5400 s of exposure time with a heat flux of 10.5 MW m−2, the total accumulated fluence of 2 × 1025 m−2 was reached. Thereafter, edge localized mode (ELM)-like thermal shocks with a duration of 1 ms and an absorbed power density of 190 MW m−2 and 380 MW m−2 were applied on the samples in JUDITH 1. During the thermal shocks, the base temperature was kept at 1000 °C. The ELM-experiments with the lowest transient power density did not result in any detected damage. The other tests showed the beginning of crack formation for every sample, except the sample pre-exposed with the pure H-beam at 1500 °C in GLADIS. This sample was roughened, but did not show any crack initiation. With exception to the roughened sample, the category of ELM-induced damage for the pre-exposed samples is identical to the reference tests without pre-exposure to a particle flux.

The high-flux deuterium plasma impinging on a divertor degrades the long-term thermo-mechanical performance of its tungsten plasma-facing components. A prime actor in this is hydrogen embrittlement, a degradation phenomenon that involves the interactions between hydrogen and dislocations, the primary carriers of plasticity. Measuring such nanoscale interactions is still very challenging, which limits our understanding. Here, we demonstrate an experimental approach that combines thermal desorption spectroscopy (TDS) and nanoindentation, allowing to investigate the effect of hydrogen on the dislocation mobility in tungsten. Dislocation mobility was found to be reduced after deuterium injection, which is manifested as a 'pop-in' in the indentation stress-strain curve, with an average activation stress for dislocation mobility that was more than doubled. All experimental results can be confidently explained, in conjunction with experimental and numerical literature findings, by the simultaneous activation of three mechanisms responsible for dislocation pinning: (i) hydrogen trapping at pre-existing dislocations, (ii) hydrogen-induced vacancies, and (iii) stabilization of vacancies by hydrogen, contributing respectively 38%, 52%, and 34% to the extra activation stress. These mechanisms are considered to be essential for the proper understanding and modeling of hydrogen embrittlement in tungsten.