In a magnetic confinement fusion reactor, the divertor is installed to remove impurities from the plasma, and tungsten (W) is considered as a promising surface material. The divertor surfaces are exposed to non-steady-state heat loads such as Edge localized modes (ELMs) and disruptions in addition to steady stare heat loads, which may cause mechanical damage and lead to equipment failure. In this study, the behavior of the surface modification of W has been investigated under ELMs-like transient heat flux loading by multiple irradiations of the negative hydrogen ion beam (3 MeV, 5 Hz) using the linear accelerator at J-PARC. In addition, a finite element analysis code has been used to simulate and analyze the temperature, stress, and strain distribution under the transient heat flux during the heating and cooling cycles. The transient heat flux caused cracks on the sample’s surface and microscopic roughness in the area inside the cracks. The surface modifications are dependent on the crystal microstructure and grain orientation. The simulation results are well agreed with the actual experimental results. During the heating process, compressive stress was generated, and during the cooling process, tensile stress was generated and exceeded the yield stress. This surface modification and cracks observed in this study are expected to affect the lifetime of the divertor and the steady-state operation of the plasma when the divertor in ITER is loaded with heat flux during the ELMs.

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