Evolution and impacts of ITER-like W/Cu monoblocks with interface damage in EAST

For ITER and BEST, it is essential to identify potential thermal fatigue damage of plasma-facing components (PFCs) and to evaluate their impact on plasma discharges before D–T nuclear fusion reaction. In 2021, ITER-like W/Cu monoblocks featuring a large chamfer (17 mm × 1.5 mm) were installed on the lower divertor target of EAST. The inclined structural design at the inter-gap of W/Cu monoblocks can reduce the probability of leading edge melting but may induce other types of damage due to a more steady-state heat flux loading on the surface, similar to the fish-scale surface of the divertor in ITER. As plasma discharges progressed, a strange phenomenon was found that bright hot spots indicative of localized thermal anomalies were frequently observed by infrared (IR) cameras, affecting approximately 41% of the modules along the toroidal direction. Subsequent investigations confirmed these anomalies primarily originated from interface damage, which significantly degraded heat transfer performance in the PFCs. IR thermography measurements combined with thermal simulations showed that interfacial heat transfer coefficient decreased to 2 × 10⁴  W (m2·K)−1 after approximately 4800 plasma discharges, resulting in an estimated 18% increase in the steady-state surface temperature. With continued operation through autumn 2022, the interfacial heat transfer conductance further decreased to 5 × 103 W (m2·K)−1, leading to a 31% increase in surface temperature. The progression of interface cracking led to an abnormal temperature rise and thus facilitated incipient melting at the leading edges of the cassette modules. As the heating power continues to rise above 10 MW, melting is expected to occur more extensively along the 17 mm × 1.5 mm chamfer. Fortunately, before the onset of melting, the existing interface cracks within W/Cu monoblocks had negligible influence on plasma discharges. These findings provide critical reference data for the long-term application of W/Cu monoblocks in ITER and future fusion reactors.