In the relentless pursuit of harnessing fusion energy, scientists are constantly testing and refining the materials that will face the extreme conditions inside tokamaks, the doughnut-shaped devices that confine the super-hot plasma where fusion reactions occur. A recent study published in the journal *Nuclear Fusion* and led by Yang Wang from the Institute of Plasma Physics at the Chinese Academy of Sciences, offers crucial insights into the performance of plasma-facing components in the Experimental Advanced Superconducting Tokamak (EAST). The findings could significantly influence the design and operation of future fusion reactors, including the international ITER project.
The study focused on ITER-like tungsten/copper (W/Cu) monoblocks, which are designed to withstand the intense heat loads in the lower divertor region of a tokamak. These components feature a large chamfer to help manage heat distribution and reduce the risk of melting. However, as Wang and his team discovered, the structural design can also lead to other types of damage, providing valuable lessons for the future of fusion energy.
“Understanding the damage mechanisms of these components is crucial for predicting their performance in ITER and other future fusion devices,” Wang explained. “Our findings highlight the importance of careful material selection and design optimization to ensure the longevity and reliability of plasma-facing components.”
After three plasma campaigns in EAST, the researchers conducted a post-mortem analysis of the W/Cu monoblocks and found significant surface damage, including crust formation, increased surface roughness, and both macro- and microcracks. The spatial distribution of this damage was strongly correlated with the heat flux distribution and the degree of misalignment. Notably, the team observed net-like cracks with four distinct morphological characteristics, attributed to variations in heat load and incident angles.
One of the most striking findings was the abnormal grain growth observed in the vicinity of the melted components, with grain sizes reaching an extraordinary 7.1 mm. This phenomenon is linked to material degradation, such as the reduction of mechanical strength, decreased fracture toughness, and increased embrittlement. Additionally, the reaction between molten tungsten and low-Z carbon impurities can form tungsten carbide (W₂C) at extremely high temperatures, further complicating the material’s performance.
The insights gained from this study are invaluable for the energy sector, as they provide a roadmap for developing more resilient plasma-facing components for future fusion reactors. By understanding the underlying mechanisms of damage, engineers can design better materials and optimize the structural design of components to withstand the harsh conditions inside a tokamak.
As the global community continues to invest in fusion energy as a clean, sustainable, and virtually limitless power source, research like this plays a pivotal role in overcoming the technical challenges that stand in the way of commercial fusion power. The findings from Yang Wang and his team not only shed light on the performance of ITER-like W/Cu monoblocks but also pave the way for innovative solutions that will bring us closer to achieving practical fusion energy.
In the words of the researchers, “These 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.” With each discovery, we edge closer to a future powered by fusion, and this study is a significant step forward in that journey.