氦离子显微镜对钨中氦行为的实验研究

摘要

针对热核聚变面向等离子体钨材料中氦泡形成、演变以及机理研究的需求,克服目前常用离子注入、电子扫描显微镜和透射电子显微镜等离线研究手段存在的不足,提出氦离子显微镜对钨中氦的上述行为原位实时在线研究方法.借助氦离子显微镜的离子注入、显微成像和聚焦离子束纳米加工功能,它可以提供能量为0.5—35 keV、束流密度可达1025 ions/(m2·s)以上的氦离子束,在该设备上进行钨中氦的注入实验.同时在注入过程,实时在线监测钨中氦泡形成、演变过程以及钨材料表面形貌的变化,原位在线分析钨材料表面氦泡的大小、迁移合并以及其诱发的钨表面和近表面的微观损伤.实验结果表明:氦离子显微镜是研究钨中氦行为演变过程及其微观机理研究的新的研究手段和强有力的实验工具.%Nuclear fusion energy is a clean and safe energy resource with huge potential. Tungsten is the primary candidate for plasma facing materials (PFMs) in future nuclear reactors because of its high melting point, high thermal conductivity and high resistance to sputtering and erosion. However, the interaction between tungsten and helium plasma generated by deuterium-tritium nuclear reactions will result in the degeneration of tungsten through helium blistering in tungsten. The solubility of helium in tungsten is low, and it tends to aggregate at grain boundary, phase boundary, vacancies and dislocations, thus forming helium bubbles. These bubbles will lead to microstructure changes of surface and bulk phases, as well as a decrease in mechanical properties, which seriously affects the service life of material. Limited by experimental techniques, some basic problems for the growth of helium bubbles in tungsten are not clear, for instance, how the helium clusters migrate, and nucleation mechanisms. The study of complex helium bubble formation, evolution and its underlying mechanism in tungsten PFM necessitates advanced experimental techniques. Traditional methods such as ion implantation, scanning electron microscope and transmission electron microscope are inadequate for this task. Therefore, we propose the helium ion microscope method to investigate the aforementioned several aspects of helium in tungsten in situ and real-time. Here, a helium irradiation experiment is performed by helium ion microscope (HIM), featuring nanostructure fabrication, ion implantation and microscopic imaging. The HIM can generate an ion beam with energy in a range of 0.5?35 keV and an flux upto 1025 ions/m2/s. In the process of helium ion implantation, we observe in situ and real time the helium blistering and the morphological evolution on tungsten surface, in order to capture the helium implantation-induced microscopic damage evolution on tungsten surface and subsurface. From the results of in situ HIM experiments, it is believed that a strong orientation dependence of blistering is observed with the blister occurring preferentially on the surface of grains with normal direction close to (111), and surface blistering of tungsten is directly related to cracks immediately below the surface. The present study demonstrates that the HIM is a powerful tool for investigating the helium blistering behavior in tungsten and provides valuable experimental data and reference for designing PFMs.