Reseach Data--Simulation and experiment investigation of lamination W structure for suppressing surface blistering

In this study, it is considered that the use of tungsten(W) foils to form laminated W structures instead of W bulk can enhance the deuterium(D) plasma irradiation resistance of W plasma facing materials(W-PFMs). The gap between the W foils in the laminated W structure acts as a gas release channel to reduce the D retention in the W-PFMs, so that the D concentration in the W cannot reach the threshold and the blistering is suppressed. Based on this viewpoint, this study first performed finite element simulations and then D plasma irradiation experiments. Fig. 1 shows the geometric schematic of the simulation part of this study with the different boundaries and domains labeled, and the geometric dimensional parameters in Fig. 1 are given in Table 1. Fig. 2(a) is a schematic of the sample in the plasma irradiation experiment. Fig. 2(b) is a schematic of the electrolytic polishing of the sample. Fig. 2(c) shows the microwave electron cyclotron resonance (ECR) plasma irradiation device used in the irradiation experiment. Fig. 3 shows the temperature field results obtained from finite element simulation. Fig. 4 shows the results of the concentration distribution of mobile D atoms obtained by finite element simulation. The thermal parameters of the material, the diffusion coefficient of D atoms in the material and the solubility parameters of D atoms in the material are listed in Table 2. The parameters of the traps in the materials used in the finite element simulations are listed in Table 3. The parameters of the recombination coefficients for D for the materials used in the finite element simulations are listed in Table 4.Fig. 5 shows the D concentration distribution curves from the finite element simulation results. Fig. 5(a, b) show the D atom concentration versus depth curves along the W symmetry axis and at the interface between W and the gap, respectively. Fig. 5(c, d) show magnified plots of the concentration distributions in Fig. 5(a, b) in the near-surface region, respectively. Fig. 5(e) shows the variation with depth of the gas pressure of D gas in the gap along the symmetry axis boundary of the gap. Fig. 5(f) shows the variation of solubility of D atoms for different materials in the temperature range derived from Fig. 3. Fig. 6 shows the morphology of the sample surface before and after D plasma irradiation. Fig. 7 shows a cross-section of the bubbles in the W bulk and W foil using FIB. Fig. 8(a, b) show the statistical results for the blisters at different irradiation fluences. Fig. 8(c, d) shows the size and area fraction of surface blisters on W foils of different thicknesses after different fluences of irradiation. Both simulation and experimental results demonstrate that the thinner the W foil thickness, the more D retention and surface blistering are suppressed. This suggests that using W foils to form laminated structure instead of W bulk is effective in utilizing the gas release channel effect for suppressing surface blistering.本研究认为，采用钨（W）箔构建层叠钨结构替代块体钨，可提升钨基面向等离子体材料（W-PFMs）的氘（D）等离子体辐照抗性。层叠钨结构中钨箔之间的间隙可作为释气通道，降低W-PFMs内的氘滞留量，使钨内氘浓度无法达到起泡阈值，从而抑制表面起泡现象。基于该观点，本研究首先开展了有限元模拟，随后进行了氘等离子体辐照实验。图1为本研究模拟部分的几何示意图，标注了不同边界与区域，图1中的几何尺寸参数见表1。图2(a)为等离子体辐照实验所用样品的示意图；图2(b)为样品电解抛光工艺的示意图；图2(c)为辐照实验中采用的微波电子回旋共振（ECR）等离子体辐照装置。图3为有限元模拟得到的温度场结果；图4为有限元模拟得到的可移动氘原子浓度分布结果。材料的热参数、氘原子在材料内的扩散系数以及氘原子在材料中的溶解度参数列于表2；有限元模拟中所用材料的捕获位点参数列于表3；有限元模拟中所用材料的氘复合系数参数列于表4。图5为有限元模拟结果得到的氘浓度分布曲线：图5(a)、(b)分别为沿钨对称轴以及钨与间隙界面处的氘原子浓度随深度的变化曲线；图5(c)、(d)分别为图5(a)、(b)中近表面区域浓度分布的放大图；图5(e)为沿间隙对称轴边界的间隙内氘气气压随深度的变化规律；图5(f)为基于图3得到的不同材料在对应温度范围内的氘原子溶解度变化情况。图6为氘等离子体辐照前后的样品表面形貌；图7为采用聚焦离子束（FIB）制备的块体钨与钨箔内气泡的截面。图8(a)、(b)为不同辐照注量下的起泡统计结果；图8(c)、(d)为不同厚度钨箔经不同注量辐照后，其表面起泡的尺寸与面积占比。模拟与实验结果均表明，钨箔厚度越薄，氘滞留与表面起泡现象便得到越有效的抑制，这说明采用钨箔构建层叠结构替代块体钨，可通过释气通道效应有效抑制表面起泡。