表面粗糙度对钨中氦起泡行为影响的原位在线研究

Fusion energy is a potential clean and safe energy resource; particularly its realization will play a key role in the energy resource requirement of China. However, one bottleneck problem is how to solve the choice of plasma-facing materials (PFM) in Tokamak as well as the future reactor. Tungsten (W) is one of the primary PFM candidate materials because of its advantages including high melting point, high thermal conductivity and high resistance to sputtering and erosion. However, the interaction of tungsten and helium plasma generated by D-T nuclear reactions, which resulted in the degeneration of tungsten due to the helium blistering in tungsten. This is of serious concern not only to the lifetime of PFM, but also to the plasma operations and device safety. Therefore, the study of helium blistering behavior in tungsten has important scientific value and engineering significance. In this project, three kinds of tungsten materials are used as samples, which including polycrystalline tungsten prepared by powder-metallurgy, polycrystalline tungsten prepared by chemical vapor deposition and single crystal tungsten. The kinds of surface roughness of samples are employed by helium ion microscope (HIM) with the ability of nanofabrication, which are quantitative characterized. The samples are implanted by helium ions, and the influence of surface roughness on helium blistering behavior in tungsten and its law are investigated by the compare of experimental results. The HIM is powerful tool combining fabrication of nanostructures imaging, ion implantation and microscopic imaging, which is of great advantage to study the above problem. The nano-surface of tungsten is prepared by HIM in order to gain the different surface roughness for tungsten. The experiment of helium irradiation is performed by HIM, which can generate an ion beam with energies of 0.5 keV-35 keV and flux of 1025ions/m2/s. The systematic influence of surface roughness on helium blistering behavior in tungsten and its laws are investigated by in situ and real time observation. The surface defect information of samples before irradiation and the helium bubble information and microstructure morphology are analyzed by transmission electron microscopy, which will provide the experimental data and reference for the design of PFM lifetime.

钨（W）作为面向等离子体材料，与聚变反应产物氦（He）会发生滞留、起泡等行为，从而导致材料辐照损伤，这不仅关系到材料的使用寿命，还会影响到等离子体的稳定性及装置的安全性。因此，研究He在W中的起泡行为具有科学价值和工程意义。在本项目中，首先利用氦离子显微镜的纳米加工能力在多晶W和单晶W表面上制备不同的粗糙度，并定量表征，然后进行He的辐照实验，最后对比实验结果分析表面粗糙度对W中He起泡行为的影响，揭示其规律。在本项目研究中，借助氦离子显微镜对钨样品进行低中能（0.5~35keV）、高通量（~1025ions/m2/s）的He辐照实验、实时在线原位研究表面粗糙度对W中He起泡行为的影响及其规律；利用透射电镜分析各种材料辐照前的表面层的缺陷信息和辐照后的He泡信息和微观结构形貌，并分析影响的微观机制，为托卡马克装置和核聚变装置中W的PFM的寿命设计提供实验数据和参考依据。

面向等离子体材料钨的表面状态在托卡马克装置中随着服役时间增长而发生改变，这将减少使用寿命且产生杂质影响等离子体稳定运行。本项目借助氦离子显微镜的离子注入、显微成像和纳米加工功能， 在钨表面定量构建不同的粗糙度，进行低中能大通量的氦离子辐照实验，且实时在线原位研究表面粗糙度对钨中氦起泡行为的影响，揭示其影响规律，分析微观机制，并给出延缓钨中氦泡形成的可能途径。.研究表明，氦离子显微镜是研究钨中氦行为的新手段方法和强有力的实验工具；借助氦离子显微镜在多晶钨、单晶钨和物理气相沉积钨表面定量构建表面粗糙度，材料表面构建特殊的结构充当He的扩散通道，减少了表面He浓度，延缓了表面起泡。粗糙表面的起泡阈值都大于理想光滑表面的阈值，在表面粗糙度为几百纳米量级时，其起泡阈值随着表面粗糙度的增加先减小后增大，表面粗糙度为300nm时起泡阈值最小；在表面粗糙度为几个微米量级时，其起泡阈值并随着表面粗糙度的增加先增大后减小，表面粗糙度为5.57μm时起泡阈值最大。对于相同表面粗糙度，台阶宽度较小的表面可能更有助于减少W表面He起泡现象，宽度间距为0.5μm时的表面不易观察到氦泡。据此，如果在材料表面构建“逸气通道”，可以减缓W表面起泡。本项目的实验结果为托卡马克装置和核聚变装置中W的PFM 的寿命设计提供实验数据和参考依据。