Interface cracking damage of W/Cu monoblocks as divertor target after high-cyclic plasma discharges in EAST

Abstract

W/Cu monoblocks will be employed in ITER as divertor targets for high heat loads. Experimental results of W/Cu monoblocks in high heat flux (HHF) tests have demonstrated their endurance on 5000 cycles at 10 MW/m2 and occasionally 300 cycles at 20 MW/m2. However, plasma-facing units (PFUs) serve in a harsh and complex environment in tokamaks and whether W/Cu monoblocks can show the same excellent properties in tokamaks needs to be further tested. Experimentally evaluating the evolution of ITER-like PFUs is one of the main missions for the EAST tokamak. The ITER-like actively cooled W/Cu monoblocks installed in the EAST lower divertor in 2021 exhibited abnormal behavior after 13,346 plasma discharges. The abnormal temperature evolution of the component was observed via infrared cameras (IR). Subsequent non-destructive testing (NDT) indicated that it might primarily arise from interface damage and scanning electron microscopy (SEM) confirmed that there were obvious cracks at the interface. The cracking center was also found above the interface. Simulation of the structural characteristics of W/Cu monoblocks under heat load in EAST can obtain temperature distribution and stress–strain distribution, which can be used to analyze the causes of material interface cracks. These findings unveil the phenomenon and mechanism of interface damage in W/Cu monoblocks after enduring over 10,000 plasma discharges in EAST, providing valuable insights for the future long-term application of W/Cu monoblocks in ITER and fusion reactors.