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Grain growth and damages induced by transient heat loads on W

During H-mode plasma in ITER, type-I Edge Localized Modes can occur naturally leading to transient heat load (<10 GW m−2) on the tungsten divertor. Such high heat fluxes might therefore induce annealing effects, such as recovery and recrystallization, or even lead to surface melting and deterioration (e.g. cracks) of the plasma-facing components. To ensure sufficient lifetime of tungsten monoblocks is thus mandatory to understand how W will evolve when exposed to such transient heat loads. We present here results on the study of grain growth and damage threshold of tungsten induced by transient heat loads (from 1 to 15 ms, <3 GW m−2). Using a high-power laser facility, we simulate ELMs and we submitted samples to various heating durations up to melting temperature. Laser heating is combined to several imaging techniques, like SEM and optical microscopy, to study grain growth and damages on W. We observed that the growth kinetics strongly depends on the repetition rate with a rapid grain growth for 100 Hz heat loads. We eventually built a finite element methods simulations, benchmarked against our experimental results, to evaluate temperature gradients and recrystallized fraction of the material when exposed to unmitigated ELMs.