Nb3Sn��������CICC�ȶ��Է���

介绍了国内首个聚变堆用Nb3Sn超导磁体模型线圈。采用一维数学模型Gandalf对其管内电缆导体(CICC)结构的超导体稳定性进行仿真,得到了CICC稳定性裕度与磁场强度和运行电流之间的关系。这对于磁体的设计和运行都有十分重要的意义。     

Nb3Sn超导电磁铁

本文报导了关于筒形Nb₃Sn磁体的研究结果。观察到磁通跳跃现象。“冻结”场的分布和历史及激发场的分布紧密相关。“冻结”场可以不是中心对称的,这进一步证明了烧结的Nb₃Sn材料是非均匀介质。我们描述了新的磁体结构,避免了磁通跳跃。除利用铁心来捕获磁通外,在激发和测量磁场的方法上均具有一定的特点。利用圆筒状Nb₃Sn作为压挤磁通的活塞,在1.5°K时,曾获得的最高场强是28.5KG。     

Nb3Sn扩散薄膜的研究

本文叙述对Nb₃Sn扩散薄膜的一项包括高场临界电流机制,合金元素作用机制等内容在内的综合性实验研究。 关键词：     

Nb3Sn复合超导体晶粒生长机制

本文研究了Nb/固态Cu-Sn和Nb/液态Cu-Sn界面上Nb₃Sn晶粒的生长。实验表明:固态-固态界面上生长的晶粒尺寸虽小(约0.1μm),但Nb₃Sn晶粒的长大仍符合通常的固态晶粒长大规律;固态-液态界面上生长的Nb₃Sn分成两层,靠近Nb的内层晶粒细小,排列致密,外层晶粒粗大,分布零散,后者是前者经过溶解/沉积过程引起的,晶体形貌大多数呈菱形十二面体,部分呈正交平行六面体,说明Nb₃Sn的{110},{100}面     

内锡法Nb3Sn超导线A15相组成及TC的特征研究（英文）

设计并制备四组不同组成的内锡法Nb3Sn单组元线和两组不同结构设计的多芯线.先将所有样品进行210℃/50hr+340℃/25hr的Cu-Sn合金化热处理,接着进行A15相成相热处理.四组单组元线的成相热处理程序是在675oC,700oC和725℃三种温度下热处理100小时和200小时;而两组多芯线的成相热处理程序是在675℃,675℃,700℃和725℃四种温度下热处理128小时和200小时.将所有热处理样品采用X-射线EDS进行A15相组成分布测定,采用SQUID磁化法测定临界温度TC.所得结果表明,经过足够热处理时间后各种内锡法Nb3Sn超导线的最终A15相组成和TC与热处理温度、导线复合体组成和结构设计以及第三元素的合金化掺杂无关,而是由这种扩散与固相反应的机制本质所决定的.     

高压下Nb3Sn单晶的超导相转变

研究高压下Nb₃Sn单晶的超导相转变行为对探究力学变形诱导的材料超导性能弱化机理有重要意义。通过分子动力学模拟研究了Nb₃Sn单晶在高压下的原子尺度变形和晶体结构变化,在此基础上,建立了高压下Nb₃Sn单晶的超导相转变模型,模型预测结果与实验观测结果吻合较好。结果表明:静水压作用下,Nb₃Sn单晶体发生了明显的晶格畸变,但晶体结构保持完整;压力诱导的费米面上电子态密度的变化在高压下Nb₃Sn单晶体超导相转变中起主导作用。所得研究结果为研究高压下Nb₃Sn多晶体以及复合多晶体的相转变行为奠定了基础,同时有助于进一步认识Nb₃Sn材料超导性能的弱化机理。     

合金元素对Nb3Sn生长动力学的影响

研究了合金元素Zr对Cu-Sn/Nb界面上Nb₃Sn生长动力学的影响。实验表明:在单芯复合材料中加入Zr显著提高了Nb₃Sn层的生长速率,层厚与时间的关系显著超过抛物线规律。这些结果不能仅用内氧化生成的ZrO₂颗粒使晶粒细化来解释,还必须考虑ZrO₂颗粒周围过饱和空位使扩散系数增大等因素。在多芯复合材料中热处理时Cu-Sn基体中Sn量的消耗,显著影响Nb₃Sn的生长。考虑了这一因素的Nb₃Sn生长动力学修正公式能对实验结果进行解释。 关键词：     

Nb/Nb3Sn复合超导材料的高压电子显微镜观察

用1000kV高压电子显微镜观察了单芯和多芯Nb/Nb₃Sn复合材料的显微组织,看到了由Nb₃Sn/Nb₃Sn晶粒重叠而成的叠栅图和Nb基体/Nb₃Sn晶粒重叠而成的叠栅图。 关键词：     

Nb3Sn超导材料的高场钉扎行为

本文利用线性回归分析法处理扩散和气相沉积Nb₃Sn带材样品以及青铜法多芯Nb₃Sn线材样品在高场(²2T)下的临界电流测试数据,得到J_c-B曲线和钉扎力随磁场变化的经验规律。该规律与Kramer模型的钉扎力公式不一致,有待提出新的理论模型加以说明。 关键词：     

Magnetization study of ITER-type internal-Sn Nb3Sn superconducting wire

Through magnetization measurement with a SQUID magnetometer the heat treatment optimization of an international thermonuclear experimental reactor （ITER）-type internal-Sn Nb3Sn superconducting wire has been investigated. The irreversibility temperature T^＊ （H）, which is mainly dependent on A15 phase composition, was obtained by a warming and cooling cycle at a fixed field. The hysteresis width △M（H） which reflects the flux pinning situation of the A15 phase is determined by the sweeping of magnetic field at a constant temperature. The results obtained from differently heat-treated samples show that the combination of T^＊ （H） with AM（H） measurement is very effective for optimizing the heat reaction process. The heat treatment condition of the ITER-type wire is optimized at 675℃/128 h, which results in a composition closer to stoichiometric Nb3Sn and a state with best flux pinning.     

Ultrasonic attenuation of surface acoustic waves in a thin film of superconducting Nb3Sn

The attenuation of 660 MHz surface acoustic waves propagating in a thin film of Nb₃Sn 5000 Å thick has been measured as a function of temperature from 4.2 K to 16 K. The A 15 Nb₃Sn, electron-beam codeposited on YZ lithium niobate and annealed at 700°C, was studied using 5.1 μm wavelength interdigital electrodes. The film revealed a transition temperature of 14.2 ± 0.1 K and using the BCS theory, an energy gap 2Δ(0) = 3.5 k_BT_c.     

Explanation for the surface dependence of the tunneling gap in Nb3Sn

An explanation is proposed for the experimental results of Hoffstein and Cohen on tunneling into superconducting Nb₃Sn. In these experiments a strong dependence of the gap on the orientation of the surface was found. This dependence is explained here in terms of the linear chain model; a [100] surface cutting only one family of niobium atom linear chains, while a [111] surface cutting all three families of linear chains.     

Acoustic soft modes of Nb3Sn in high magnetic fields

In single crystal Nb₃Sn the effect of a magnetic field upon the soft sound velocity v_s (110, 1$\text{1}$0) was measured at different temperatures above the structural phase transition point. The observed quadratic variation with field is in accordance with theory. But the magnitude of the field dependence is much smaller than expected and can only be explained by existing theories if the magnetic moment of the electron would vary by as much as a factor of two within an energy interval of some 100 K.     

Influence of electronic structure on superconducting properties of complex crystals: Theory and application to Nb3Sn

A thermodynamic theory valid for complex crystalline superconductors is applied to Nb₃Sn. It is shown how the structure of the Eliashberg equation and the solution is altered by density of states fine structure. One important implication is that the current method of inversion of tunneling data can be only approximate.     

Effect of sputtering anisotropic ejection on the optical properties and residual stress of Nb2O5 thin films

The effect of sputtering anisotropic ejection on the optical properties and internal stress of niobium pentoxide (Nb₂O₅) films prepared by ion-beam sputtering deposition (IBSD) was investigated experimentally. Thin films were deposited on unheated BK7 glass substrates and silicon wafers at different ejection angles surrounding a metal target. The ejection angles varied from 0° to 75° in increments of 15° for each substrate. It was found that the optical constants of the Nb₂O₅ films were significantly influenced by the sputtering ejection angle. The surface roughness and residual stress in the Nb₂O₅ thin films were also found to vary with the ejection angle. In this work, Nb₂O₅ films had a higher refractive index, lower absorption, lower stress and lower roughness when films deposited at an ejection angle of 30°.     

Ordering of Nb3Sn layer formed in the bronze process - I

A study of ordering of superconducting Nb₃Sn layers formed in the bronze process has been attempted for the first time. The multifilamentary composites containing 10,000 niobium filaments embedded in a bronze matrix have been diffusion reacted at various temperature for short durations of a few minutes, and the resulting changes in T_c are systematically analysed. The data are discussed in terms of a reordering kinetics model and the values of various activation energies determined are found to be consistent.     

超导离子源铌三锡六极线圈镜像磁场约束结构的优化设计

中国科学院近代物理研究所正在进行国际首台45 GHz全铌三锡超导离子源FECR(Fourth Electron Cyclotron Resonance)磁体的研制,该离子源磁体线圈由六个铌三锡超导六极线圈和四个铌三锡超导螺线管线圈组成。由于单根超导线绕制异形六极线圈(非标准鞍型)技术难度大,且铌三锡超导性能对应力敏感,为了测试单个铌三锡六极线圈性能能否达到设计指标,基于铝合金壳层结构和Bladder-Key精确预紧技术,设计了镜像磁场约束结构。本工作主要阐述了运用ANSYS参数化设计编程对镜像磁场结构进行优化设计的过程和优化后的镜像磁场结构,确定了室温预应力大小,并给出了线圈经过室温预紧、冷却降温和加电励磁后的最大等效应力。进一步结合实际六极线圈制作公差(±0.1 mm),分析和评估了公差对镜像磁场结构中六极线圈预应力施加的影响。