低温下氢同位素形核的动力学过程及其晶体力学性能研究

Inertial confinement fusion (ICF) will be one of the most effective solutions for future world’s energy demands. Many experiments have been employed to make cryogenic deuterium (D) – tritium (T) targets since the targets are very important in the ICF research. However, it is difficult to make targets with uniform DT fuel layers, in particular, the formation mechanics of uniform and smooth DT ice layers and the changes of the structure of targets with the change of temperature are not clear. It is essential to investigate the formation of good targets and their complicated mechanical properties. In this project, the process of the nucleation of hydrogen isotope (H2、D2、T2 and their compounds) crystals will be studied at low temperatures, and the physics image of the nucleation and growth of hydrogen crystals and the main factors that affect the nucleations will be explored. Therefor, theoretical principles of well known crystal growth will be provided for controlling the direction of nucleation and subsequent growth of single hygrogen crystals to uniform ice layer. The mechanical properties of hydrogen isotope crystals will be investigated in detail. The elastic properties of hydrogen crystals, the effects of temperatures and stress on the structures of crystals, and the formation mechanism of the roughness of solid DT layers can be obtained. Finaly, cooling-induced roughness of solid cryogenic targets can be controlled based on these researches. The research of this project is helpful for the design and fabrication of excellent cryogenic DT targets.

惯性约束聚变有望成为解决未来世界能源需求问题的最有效途径之一。低温氘氚冷冻靶对于惯性约束聚变的研究至关重要，因此，实验上对冷冻靶已经进行了较详细的研究，但要制备出均匀分层、表面光滑的冷冻靶并非易事，因此从根源上探究高质量冷冻靶的形成机理及其复杂的力学性能非常必要。本项目通过计算机模拟研究低温下氢同位素（H2、D2、T2及其化合物）晶体形核和生长的基本过程，揭示氢晶体形核的物理图像及影响形核的主要因素，为控制氢同位素晶体形核的方向性和氢单晶生长为均匀的氘氚层提供理论基础；并对氢同位素晶体的力学性能进行详细研究，以期获得氢晶体的力学弹性性能，分析温度、应力等对氢固体结构的影响，揭示氘氚冰层表面粗糙的形成机理，为控制冷却过程中固体氘氚靶的表面粗糙度提供理论基础。通过本项目的研究为最终制备出性能优良的固体氘氚冷冻靶提供理论依据。

低温氘氚冷冻靶对于惯性约束聚变的研究至关重要，因此从根源上探究高质量冷冻靶的形成机理及其力学性能非常必要。本项目通过计算机模拟初步研究了氢同位素晶体在聚变环境中的行为。采用VASP主要研究了：hcp和fcc氢同位素晶体的结构及其力学参数，发现fcc中的Pa3结构最稳定，而hcp结构中无序结构的能量最低，计算了hcp和fcc结构氢分子晶体的弹性常数和弹性模量；研究了hcp和fcc氢同位素晶体中缺陷的行为，包括空位和间隙氢分子的形成能及其稳定结构，以及缺陷的迁移路径和迁移能、氢分子的迁移激活能等；研究了hcp铍（0001）和fcc铜（111）表面上氢同位素分子的吸附情况。拟合了氢分子间和氘分子间相互作用势，将该作用势嵌入到经典分子动力学程序中，模拟计算了氢晶体的力学性能，以及.球形氢分子晶体在不同压强和温度下晶体表面结构的变化，采用粗糙度表征了表面结构的变化情况；采用氢分子作用势和文献中的铍-氢作用势，初步模拟了铍（0001）表面上不同浓度的氢分子在不同基底温度下的行为，模拟结果显示氢晶体的形核与生长与氢分子的浓度、重力和基底温度密切相关。为了改善铍表面氢分子的形核，重新拟合了铍-氢相互作用势。通过本项目的研究为最终制备出性能优良的固体氘氚冷冻靶提供理论依据。