铝中氦原子行为的密度泛函研究

用密度泛函理论计算了大量He原子存在时He在金属铝中不同位置的能量,并在理论上预测了铝中的氦原子行为.结果表明,铝晶胞内He原子择优占位区是空位,而在整个晶体范围,最有利于容纳He原子的区域是晶界,其次是空位和位错.在fcc-铝的两种间隙位中,He原子优先充填四面体间隙位.间隙He原子的迁移能很小,易于通过迁移在晶内聚集,或被空位、晶界、位错等缺陷束缚.     

铝中氦原子行为的密度泛函研究

用密度泛函理论计算了大量He原子存在时He在金属铝中不同位置的能量,并在理论上预测了铝中的氦原子行为。结果表明,铝晶胞内He原子择优占位区是空位,而在整个晶体范围,最有利于容纳He原子的区域是晶界,其次是空位和位错。在fcc-铝的两种间隙位中,He原子优先充填四面体间隙位。间隙He原子的迁移能很小,易于通过迁移在晶内聚集,或被空位、晶界、位错等缺陷束缚。     

铒、钪膜中离子注入氦的热解析行为

采用热解析法初步研究了铒、钪膜中离子注入氦的热解析行为。研究结果表明:同种元素铒中离子注入氦的热释放峰位相同,但膜的致密性将影响氦的释放量,结构疏松的膜中存在的孔洞是氦的快速释放通道;在相同注入剂量和能量条件下,铒、钪膜中注入氦的热释放峰位不同,这可能与氦在铒、钪膜中的深度分布及膜的致密性有关,利用质子增强背散射法测量出能量为60 keV的4He+在铒、钪膜中的注入深度分别为210,308 nm。     

α-Fe中氦泡极限压强的分子动力学模拟

为了深入认识α-Fe中氦泡冲出位错环的微观机制,有必要研究α-Fe中氦泡冲出位错环时的极限压强特性.本文建立金属-氦泡的立方体型代表性体积单元模型,针对8种不同初始半径的球形氦泡,以初始氦空位比为变量,开展分子动力学模拟,得到了各模型中位错环开始形成时的氦泡极限压强和临界氦空位比.研究结果表明:对于无量纲半径介于2—10的氦泡,冲出位错环时的氦泡极限压强和临界氦空位比均随着氦泡初始半径的增大而非线性减小;基体中氦泡冲出位错环时的临界氦空位比具有明显的尺寸效应;初始时刻(0 ps),在经过立方体型模型中心的横截面上,氦泡周围Fe原子阵列的剪应力集中和最大剪应力出现在对角线与氦泡边界交点(即45°)处,并且关于横截面上平行于边的两条对折线对称分布,剪应力集中区的范围和最大剪应力均随着初始氦空位比的增大而增大;位错环冲出方向对应最大剪应力方向.本文的研究加深了对金属中氦泡物理特性的认识,为后续分析氦泡对材料宏观物理和力学性质的影响奠定了有益的基础.     

温度及深度对钛中氦泡释放过程影响的分子动力学研究

利用分子动力学模拟方法对温度及He泡深度给金属Ti内He泡的体积、压强和释放过程等带来的影响进行了研究. 首先, 通过研究室温下He泡在金属Ti内不同深度处的状态, 得到He泡的形状、压强、体积等物理量随其深度的变化规律. 发现He泡压强随其深度增加逐渐变大, 体积则逐渐减小, 但当He泡深度增大到2.6 nm时, 二者均维持在某个固定值附近. 然后对包含有He泡的Ti体系在温度作用下的演化过程进行了模拟, 发现不同深度处He泡从金属Ti内释放出来所需要的临界温度有很大差别, 总体来看He泡越深, 释放所需的临界温度越高. 但不同温度下He原子的释放速率没有明显差别, 释放过程几乎均为瞬间完成. 最后通过对He泡内部压强和其上方金属Ti薄层的抗张强度进行统计对比, 阐述了金属Ti 体内He泡的释放机制: 当He泡内部压强大于其上方Ti薄层抗张强度时, He泡就会将Ti 薄层撕裂, 从而使He原子得到释放.     

氦在球磨贮氢合金中的存在行为研究

通过正电子寿命测量及结构分析，研究了氦气氛球磨LaNi4.75Al0.25和Zr50Co50贮氢合金中氦的存在行为.研究结果表明：随着气氛压力增加，氦的溶入量增加，相对而言，LaNi4.75Al0.25更有利于氦的溶入；球磨样品正电子寿命的特征参数发生变化，这表明氦在材料中存在行为的差异；对于Zr50Co50合金，氦首先填充在超细晶粒的三叉晶界或空位团处，随着气氛压力增加，有小部分氦填入单空位的自由体积处，形成空位-氦复合体；对于LaNi4.75Al0.25合金，氦首先进入单空位大小的自由体积中，形成空位 关键词： 正电子寿命 氦引入 高压球磨 贮氢合金     

Structure stability and electronic properties of the Zr-He system: First-principles calculations

Ab initio studies are carried out for the atomic and electronic structures of the Zr-He system. It is revealed that zirconium undergoes a phase transition induced by helium. The most preferred position of the impurity in the metal lattice is determined. The energy of dissolution of helium and the excess volume introduced by helium are calculated. It is shown that the presence of helium in the Zr lattice significantly perturbs the valence charge density of the metal and substantially changes its electronic structure.     

Molecular dynamics study of helium bubble pressure in titanium

In this paper,the pressure state of the helium bubble in titanium is simulated by a molecular dynamics(MD) method.First,the possible helium/vacancy ratio is determined according to therelation between the bubble pressure and helium/vacancy ratio;then the dependences of the helium bubble pressure on the bubble radius at different temperatures are studied.It is shown that the product of the bubble pressure and the radius is approximately a constant,a result justifying the pressure-radius relation predicted by thermodynamics-based theory for gas bubble.Furthermore,a state equation of the helium bubble is established based on the MD calculations.Comparison between the results obtained by the state equation and corresponding experimental data shows that the state equation can describe reasonably the state of helium bubble and thus could be used for Monte Carlo simulations of the evolution of helium bubble in metals.     

Radon as a tracer for helium exploration in geothermal areas

High heat flow and weak structural features in geothermal areas allow easy passage for release of subsurface gases to the atmosphere. In particular, radon and helium are constantly transported from the earth's interior and vented out through exhalation points in permeable fault zones. At some places unusually large concentrations of helium may be encountered in soil airs. The possibility of trapping the released helium for bulk use has recently emerged. Because of its highly dispersive nature, helium is a difficult gas to detect during field explorations. Radon monitoring is thus taken up to locate structurally weak zones that allow helium permeation. The technique was recently adopted to determine high helium exhalation points in the Birbhum–Santhal Paragana geothermal area.     

氦原子及类氦离子基态能量的经验公式

通过对氦原子和类氦离子电离能数据的分析 ,找到了一个能够快速计算类氦体系基态能量的经验公式 ,验算了一些类氦离子 (Z=2— 1 5 )的基态能量 ,与实验测量值符合得很好。除了 Li 和 Be 的基态能量的相对偏差为 0 .4 46 %外 ,其他的都低于 0 .4 %。     

氦离子显微镜对钨中氦行为的实验研究

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 ke V、束流密度可达10~(25) ions/(m~2·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.     

Dipole moments of molecules solvated in helium nanodroplets

Stark spectra are reported for hydrogen cyanide and cyanoacetylene solvated in helium nanodroplets. The goal of this study is to understand the influence of the helium solvent on measurements of the permanent electric dipole moment of a molecule. We find that the dipole moments of the helium solvated molecules, calculated assuming the electric field is the same as in vacuum, are slightly smaller than the well-known gas-phase dipole moments of HCN and HCCCN. A simple elliptical cavity model quantitatively accounts for this difference, which arises from the dipole-induced polarization of the helium.     

中国固态增殖剂试验包层系统的氦气冷却系统仿真计算

根据中国固态增殖剂试验包层氦气冷却系统的系统设计和布置情况,利用大型一维流体仿真软件 Flowmaster 建立了氦气冷却系统的仿真模型。利用该仿真模型,模拟了氦冷系统在产氚包层系统不同工况下氦气流动情况以及各种参数的分布情况,得到了热等待工况、热备用工况、正常运行工况和除氚工况下系统的主要工艺点的温度、压力和流速分布等相关参数,为系统的设计和设备选型提供参考。同时,该仿真模型和结果对中国聚变工程实验堆氦冷系统的仿真模拟具有一定的参考意义。     

The influence of defects in the crystal structure on helium diffusion in quartz

The solubility and diffusion of helium in quartz crystals are investigated as functions of the distribution and density of structural defects. The types of defects in the crystals are identified and their distribution over growth sectors is determined by x-ray diffraction topography and phase radiography with a synchrotron radiation source. The effective solubility and effective diffusion coefficients for helium in quartz are estimated from the experimental data on the amount of helium extracted from samples with different contents of defects. It is revealed that the effective diffusion coefficient of helium depends on the number of dislocations.     

Probing helium interfaces with light scattering: From fluid mechanics to statistical physics

We have investigated the formation of helium droplets in two physical situations. In the first one, droplets are atomised from superfluid or normal liquid by a fast helium vapour flow. In the second, droplets of normal liquid are formed inside porous glasses during the process of helium condensation. The context, aims, and results of these experiments are reviewed, with focus on the specificity of light scattering by helium. In particular, we discuss how, for different reasons, the closeness to unity of the index of refraction of helium allows in both cases to minimise the problem of multiple scattering and obtain results which it would not be possible to get using other fluids.     

HL-1M托卡马克氦输运和排除

研究了HL－1M托卡马克常规欧姆放电和改善的束状态下的氦输运和排除,并与一维蒙特卡罗中性氦输运程序IDHET的计算结果进行了比较。实验结果表明,真空泵能有效地抽除辉光放电清洗后在剩余气体中的氦,使真空室内的氦趋于一个较低的固有水平。在改善约束实验中,发现氦有积累增加的趋势,氦谱线发射强度径向分布峰向内移,在对总体约束影响很小的情况下,利用低水平的MHD扰动,采取LHCD与ECH辅助加热功率组合等进行了一些选择性排氦实验,并对将来堆条件下或HL－2A装置上利用射频场有质动力改善排氦效率的前景进行了讨论。     

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According to the system design and arrangement of helium cooling system of China helium cooled ceramic breeder (CHCCB), helium cooling system simulation model is built using large one-dimension fluid simulation software Flowmaster. For different operation conditions of tritium breeding blanket system, helium flow conditions and parameter distribution are simulated for helium cooling system, using such simulation model. Temperature, pressure and velocity distributions and other related parameters have been obtained on different scenarios for hot waiting state, hot standby state, normal operation state and tritium out-gassing state, which provide reference for the design of system and equipment selection. Meanwhile, the model and simulation results have some reference significances for the simulation of helium cooling system for CFETR.     

Helium effects on the microstructural evolution of reactor irradiated ferritic and austenitic steels

Abstract

Microstructural evolution in neutron irradiated austenitic stainless steels and Cr-Mo ferritic steels is reviewed. Important highlights are: (1) there is a strong correlation between precipitation and void evolution in austenitic steels; (2) helium affects precipitate evolution in austenitic steels, but observations indicate no effect on precipitation in ferritic steels; (3) helium has a pronounced effect on the cavity evolution of the two steel types. Helium effects are explained in terms of the interrelationship between microstructural evolution and point-defect annihilation processes. In stainless steel, three relative regimes of microstructural behavior for different helium generation rate-displacement rate ratios are recognized: (1) “low” He/dpa ratio, where helium effects on the radiation-induced microstructural evolution are negligible or develop slowly, (2) “medium” He/dpa ratio, where helium effects strongly enhance the microstructural changes, and (3) “high” He/dpa ratio, where helium effects are limited to the early development of a high density of fine bubbles which interfere with other radiation-induced microstructural changes, but allow enhanced thermal microstructural evolution to take place instead. The extensive data on austenitic steels fall within these regimes. Ferritic steels are known to be highly resistant to void swelling without helium. It is suggested that enhanced cavity formation due to helium in ferritic steels makes higher swelling a potential concern for fusion reactor applications.     

Molecular Dynamics Simulations of Helium Behaviour in Titanium Crystals

Molecular dynamics simulations are performed to investigate the behaviour of helium atoms in titanium at a temperature of 30OK. The nucleation and growth of helium bubble has been simulated up to 50 helium atoms. The approach to simulate the bubble growth is to add helium atoms one by one to the bubble and let the system evolve. The titanium cohesion is based on the tight binding scheme derived from the embedded atom method, and the helium-titanium interaction is characterized by fitted potential in the form of a Lennard-Jones function. The pressure in small helium bubbles is approximately calculated. The simulation results show that the pressure will decrease with the increasing bubble size, while increase with the increasing helium atoms. An analytic function about the quantitative relationship of the pressure with the bubble size and number of helium atoms is also fitted.