利用复合原子力显微镜技术研究低能高流强He+导致的钨材料辐照损伤机制

Due to its high-Z, high melting temperature, high thermal conductivity, and low sputtering yield, tungsten is regarded as the most promising candidate for the plasma-facing materials of fusion reactors. Tungsten suffers the irradiation damage by high 14 MeV neutrons and low-energy (tens of eV to several keV) and high-flux (10^22-10^24/m2.s) helium and hydrogen ions, causing the degradation of material properties. The understanding of the behavior of W materials in fusion environment is a major issue of the material-related stake of fusion reactors. In this work, combined atomic force microscopy techniques (including tapping mode atomic force microscopy combined with conductive atomic force microscopy, nano-indentation tests combined with conductive atomic force microscopy, atomic force microscopy combined with focused ion beam technology) are used to study the irradiation damage of tungsten. The low-energy and high-flux helium ions irradiation induced surface diffusion, coalescence process, the depth of penetration, the spatial distribution of defects and bubbles is analyzed in situ. The resulting changes in the micro-topography of tungsten materials, surface swelling, conductivity, hardness are also evaluated. The irradiation defects formation and evolution discipline of low-energy and high-flux helium ions irradiated tungsten are summarized. Combining the experiment and computer simulations, the irradiation damage mechanism of tungsten is discussed. This work undoubtedly make a great progress on the understanding of irradiation damage mechanism of plasma facing materials and provide a useful reference for the concept design of key materials for fusion reactor.

钨材料具有高质量数、高熔点、高热导率、低溅射率等优点，被认为是最有前景的一种面向等离子体材料，在核聚变反应堆中，14 MeV中子辐照以及低能(几十eV至几keV)大流强（10^22-10^24/m2.s）H/He离子流的轰击导致钨材料性能急剧下降。因此，研究钨材料在聚变环境中的辐照损伤行为至关重要。申请人拟采用复合原子力显微镜技术(包括高分辨轻敲原子力显微镜和导电原子力显微镜复合、导电原子力显微镜与纳米压痕技术复合、原子力显微镜与先进的聚焦离子束技术复合）原位分析低能高流强氦离子在钨材料表层扩散和聚结、渗入深度、缺陷和气泡的空间分布，以及由此引起钨材料在微观形貌、表面肿胀、导电性、微硬度等特性的变化，研究辐照诱导的钨材料损伤生成及演化规律，同时结合理论模拟探讨钨材料的辐照损伤机制。这对进一步理解聚变堆面向等离子体材料的辐照损伤机制，推动聚变堆关键材料的概念设计上具有重要意义。

钨材料被认为是未来聚变反应堆上最有可能应用的一种面向等离子体材料，因此，研究钨材料在聚变环境中的辐照损伤行为至关重要。本项目开展的主要研究工作及取得的成果包括：升级改造了等离子体辐照实验平台，优化了离子源结构和放电参数，将离子束流强提高了两个数量级，由1021ions/m2•s提高到1023ions/m2•s，可实现长时间大剂量稳态辐照实验；系统开展了低能大流强氦离子束辐照钨材料的实验工作，考察了离子剂量、能量、温度等参数变化对钨材料表面结构演变过程的影响，分析了纳米钨丝的生长机制，研究发现当氦离子能量>70eV, 辐照温度>1300 K时更易形成纳米钨丝，并对其生长的机制进行了深入的分析；对比研究了导电原子力显微镜和透射电子显微镜在分析材料辐照缺陷方法上的差异，分析表明导电原子力显微镜对样品表面（深度<20 nm）的缺陷或气泡分布的检测更加灵敏，模拟结果也表明当针尖与缺陷的距离从2 nm增加至50 nm时，电阻值增加了3-6个数量级，检测灵敏度急剧下降。这些工作对于进一步理解钨材料的辐照损伤机制，优化钨材料设计等方面具有重要参考意义。