Surface damages of ITER-like W/Cu monoblocks in the lower divertor of EAST

Abstract In future ITER operations, it is crucial to maintain the performance of plasma-facing components, particularly in regions subject to high thermal loads. Studies on component damage in existing tokamaks provide important reference data for predicting potential damage in ITER and future fusion devices, ensuring the most effective response strategies during future operations. In 2021, ITER-like W/Cu monoblocks featuring a large chamfer (1.5 mm × 17 mm) were installed on the lower divertor target of EAST. The structural design of W/Cu monoblocks with inclination angles can reduce the probability of melting but may also induce other types of damage, similar to the fish-scale surface of the divertor in ITER (toroidal bevel with a depth of 0.5 mm). After three plasma campaigns, post-mortem analysis identified significant surface damages, including crust formation, increased surface roughness, macrocracks, and other types of damage. The spatial distribution of damage is strongly correlated with the heat flux distribution and the degree of misalignment. At the leading edge areas, macrocracks are caused by plastic strain under steady-state heat loads, while microcracks are brittle cracks mainly caused by transient heat loads. The net-like cracks displayed four distinct morphological characteristics, attributed to variations in heat load and incident angles. Abnormal grain growth was observed in the vicinity of the melted components, with grain sizes reaching an extraordinary 7.1 mm. Both the formation and propagation of cracks were related to material degradation, such as the reduction of mechanical strength, the decrease in fracture toughness, and increased embrittlement. Molten tungsten (W) and low-Z carbon impurities can react to form tungsten carbide (W 2 C) at extremely high temperatures. Such damages on W/Cu monoblocks for the lower divertor in EAST provide critical insights into the service performance of these ITER-like W/Cu monoblocks, which can provide important reference data for the future use in ITER and other fusion reactor devices.