氢同位素在高能重离子辐照钨中的等离子体驱动渗透行为研究

Tungsten (W) is currently considered as the leading first wall material for DEMO and future fusion reactors. Under hot first wall operation scenario, hydrogen isotopes (deuterium (D) and tritium (T), to be referred to as H) from the edge plasma will permeate through W into the blanket module, which will lead to the contamination of the coolant and the loss of treasured T. Moreover, the H permeation behavior could be influenced due to that the irradiation defects, which are produced by high energetic fusion neutrons, interact with the H atoms in W lattice. So far, researches on the effects of irradiation defects on the H permeation through W material are seldom carried out and the relevant mechanisms are unclear. In this project, various ion beam irradiation methods will be used to produce irradiation defects (like dislocations, vacancies and helium bubbles) in W, then the effects of these defects on the H permeation behavior (eg., steady state permeation flux, effective diffusion coefficient) through W will be studied. The relevance between H permeation behavior and defect type/concentration is expected to be understood and underlying mechanisms will be clarified. Besides, the H permeation behavior of irradiated W under different plasma conditions (eg., incident flux/ion energy, or even tokamak plasma) will be studied, and the correlative PDP mechanisms will be interpreted. These researches will give a solid theoretical support to the prediction of T permeation behavior through W first wall under neutron irradiation, and provide data support to the engineering design and nuclear safety analysis for CFETR and DEMO.

DEMO及未来聚变堆设计中多采用金属钨作为第一壁材料。在热壁模式运行时，边界等离子体中的氢同位素（氘、氚，简称氢）将渗透穿过钨壁进入包层模块，造成冷却剂污染和氚漏失。尤其在高通量14.1MeV聚变中子辐照下，钨材料中将形成各种缺陷累积；缺陷与氢作用将影响氢渗透行为，然而具体影响机制目前尚不清晰。本项目拟采用多种高能重离子束模拟中子辐照在钨材料中产生辐照缺陷，对缺陷类型（如位错、空洞、He泡）进行判别和设计调控；同时结合实验室和托卡马克等离子体研究辐照钨中的等离子体驱动渗透行为，揭示不同缺陷类型对钨中氢稳态渗透通量、有效扩散系数等的影响与微观作用机理，阐明不同辐照钨中氢渗透物理机制。项目成果能为聚变中子辐照下的第一壁钨中氚行为预测提供参考，为CFETR和DEMO堆的氚在线循环精确计算和核安全评估提供科学支持。

本项目针对聚变中子辐照下第一壁钨中的等离子体驱动H渗透行为展开研究。.项目首先揭示了不同等离子体条件下钨材料中 H 渗透的物理机理。利用直线等离子体装置PREFACE平台，考察了钨中等离子体驱动H渗透行为在不同温度区间的控制机制、不同样品表面状态对H渗透行为的影响。结果表明，不同温度区间H渗透行为由不同机制控制：700-900 K，H渗透量随温度升高而升高，为 RD 机制；900-973 K，H渗透量随温度升高略有下降，为RR 机制。无论RD或 RR 机制，钨中的低能等离子体驱动渗透行为均受到前表面状态的影响。这与钨表面C、O等杂质被溅射后H表面再结合系数改变有关。完成 EAST 托卡马克中H渗透平台的建设，已在壁处理过程中测得了氘渗透信号。.此外，项目深入阐明了不同类型的辐照缺陷对钨中H渗透行为影响的微观机制。分别采用高能Au3+、He+模拟聚变中子辐照在钨中产生不同类型缺陷（位错环、空洞、He泡等），然后利用正电子湮没多普勒展宽谱、透射电镜等对缺陷进行表征，最后研究了各缺陷对H渗透的影响。结果表明：位错环、空洞均使首轮渗透达到稳态所需时间增加，即首轮H扩散系数增大；但后续轮次的扩散系数与未辐照钨中相当。辐照空洞、位错环形成并未影响H渗透系数。结合不同缺陷在钨中的H捕获能分析表明：空洞为不可逆H捕获缺陷，其对H的捕获使首轮H扩散系数降低但不影响后续扩散；位错环为可逆H捕获缺陷，其始终影响H扩散；但由于其密度相对较低，对扩散系数的影响不明显。渗透系数为H渗透达稳态时测定，空洞等不可逆缺陷由于在稳态渗透时已不发挥作用，因此对渗透系数无影响；位错为可逆H捕获缺陷，稳态渗透时仍产生作用，但此时其捕获的H与晶格位点中的H已处于局域热力学平衡，不改变H的扩散截面，因此不会影响H渗透系数。.本项目成果能为聚变中子辐照下的第一壁钨中氚行为预测提供参考。