极端环境光学测量技术及其在超导材料特性研究中的应用

发布时间：2018-01-05 08:36

本文关键词：极端环境光学测量技术及其在超导材料特性研究中的应用　出处：《兰州大学》2017年博士论文　论文类型：学位论文

【摘要】：超导材料因其独特的物理特性如零电阻效应、迈斯纳效应、约瑟夫森效应等在能源、交通和微电子等领域具有广泛的应用前景。目前采用高温超导薄膜和超导带材如由Bi系、及Y系涂层导体制造的超导量子干涉仪(SQUID)、超导限流器、强磁场磁体等已实现商业化生产,有力的推动了科学研究和生产生活。在这些应用当中超导材料通常处在极低温、电、磁复杂环境,其热失配及自身所承载的电磁力往往导致超导材料发生变形,而已有的研究表明超导体的三个基本参数即临界温度,临界电流密度和临界磁场均与力学变形有关。以临界电流为例,早在1976年研究人员发现拉伸变形会显著降低3Nb Sn超导材料的临界电流密度。后来的观测表明,各种力学变形(拉、弯、扭)均能引起临界电流密度的退化。然而目前,针对这个问题的研究集中在材料表面变形(应变片测量)与临界电流相关性的研究中,而对于材料变形过程中的内部损伤产生、演化及其对临界电流的影响鲜有研究。究其原因在于目前常用的材料内部损伤观测技术如X射线、CT扫描等均难以在此极端环境下有效开展。因此,在极低温、电磁复杂环境下寻找新的超导材料内部损伤的观测方法即磁光技术将有望解决超导材料临界电流随应变退化这一困扰学术界多年的关键科学问题。本博士学位论文主要包括两个部分的内容,即超导薄膜样品的全场热、磁应力实验测量技术及相关的理论框架和超导带材内部损伤原位观测技术的研究,取得的主要成果如下:(1)首先从理论上分析了低温空气介质对CGS系统曲率测量及其误差因子的影响,其次针对多层介质对薄膜曲率测量的影响,提出一个修正因子,采用空气、水和硅油三种介质进行对比实验,验证了修正因子的正确性。最后考虑到某些特殊情形如薄膜模量过大、载荷相对较小时会得到稀疏的干涉条纹,造成薄膜应力分析的难度过大且准确性降低,提出一种相位参数化的干涉条纹倍增技术,相比传统的条纹倍增技术,该技术不仅实现了任意倍的条纹倍增,且可实现直流分量和主频分量的有效分离。采用传统的光测弹性力学技术,验证了该方法的可靠性。(2)建立了包含磁体力薄膜类材料的曲率与应力之间关系的理论计算模型,讨论了轴对称和非轴对称情形下其与Stoney理论框架的关系与区别。结果表明,含有磁体力的薄膜应力与曲率的理论模型是难以退化到基于错配应变得到的Stoney理论模型。在完成理论模型的基础上,研制一套具有观察窗(直径50mm)、制冷机直接冷却(最低至30K)、温度连续变化可控(控温精度0.1K)且包括外加励磁装置(磁场精度0.1mT)的光学测试系统,将相干梯度敏感方法(CGS)拓展至低温、磁场复杂环境,从而实现了超导薄膜材料在冷却过程和磁化过程中全场的曲率测量。通过方法改进,首次获得了超导薄膜在脉冲磁场作用下的全场应力分布及其随时间的演化特征,为超导薄膜在脉冲磁场环境下的应用安全分析提供了参考依据。(3)参与研制极低温、电、磁、力多环境场超导材料特性测试仪器,负责设计一种光学对焦技术,解决了显微物镜在冷却过程中因抽真空产生压差和低温材料变形引起的对焦困难。与此同时,提出一种自适应方法用于亮度-磁场标定,成功解决了非均匀照明下的磁场标定这一难题。在此基础上,针对YBCO涂层导体开展了二类典型实验。第一,研究了拉伸应变对其临界态稳定性的影响。超导带材零场冷却至超导态后,施加一定的外磁场在其边缘形成稳定的临界态。逐步增大拉伸应变至0.6%后,局部磁通在混合态区域开始成核移动。随着应变的进一步加大,局部磁通从混合态区向迈斯纳区域进行穿透,直至Meissner区域完全破坏。实验结果表明,磁通穿透深度满足应变的指数规律,且其穿透速度的量级在1um/s至1mm/s之间。第二,研究了超导带材载流时自场下拉伸应变引起的损伤及失超相关规律。超导带材零场冷却至超导态后,施加100A的恒定电流,逐步增大拉伸应变至0.62%时,磁通开始移动,随着应变进一步增加,磁通向迈斯纳区穿透,最后整体迅速失超。
[Abstract]:Superconducting materials because of its unique physical properties such as zero resistance effect, Meisner effect, Joseph Sen effect in energy, and has wide application prospect areas of transportation and microelectronics. The high temperature superconducting thin films and tapes such as a Bi system, and Y coating conductor manufacturing superconducting quantum interferometer (SQUID), superconducting fault current transformer, high field magnets have achieved commercial production, a strong impetus to the scientific research and production life. In these applications of superconducting materials are usually at extremely low temperature, electrical, magnetic and complex environment, the thermal mismatch and the electromagnetic force of its bearing often leads to superconducting material deformation, and the studies have shown that three the basic parameters of superconductor is the critical temperature, critical current density and the critical magnetic field and mechanical deformation related to the critical current. For example, the tensile deformation will significantly reduce the 3Nb Sn early in 1976, the researchers found The critical current density of the superconductor. Later that observation, all kinds of mechanical deformation (tensile, bending, torsion) can cause degradation of critical current density. However, research on this issue focus on the material surface deformation (strain gauge) and study the critical current of the association, and for the internal damage process the deformation of materials, little research evolution and its effect on the critical current. The reason is that the current commonly used material internal damage observation technology such as X ray, CT scan in this extreme environment are difficult to carry out effectively. Therefore, at extremely low temperature, electromagnetic environment observation method for complex injury of the new superconducting materials internal magnetic optical technology is expected to solve the key scientific problems of critical current superconducting materials with strain degradation that plagued the academic years. This dissertation mainly includes two parts, namely The thermal conductivity of thin film samples, magnetic stress measurement technology and the related theoretical framework and the internal damage of superconducting tapes in situ observation technique, the main results are as follows: (1) first from the theoretical analysis of the low temperature air medium on the CGS system to measure curvature and its error factors. Secondly, the influence of multi-layered media the film curvature measurement, proposed a correction factor, by air, three water and silicone oil were compared to verify the correctness of the correction factor. Finally, considering some special cases such as the film modulus is too large, the load is relatively small interference fringes will get sparse, resulting in stress analysis of thin films had difficulty and reduce the accuracy of the interference fringes, proposed a parametric phase multiplication technique, compared with the traditional technique of the fringe multiplication fringe times this technique not only implement arbitrary times increase, and can achieve The effective separation of the DC component and frequency components. The traditional photoelasticity technique, the reliability of the method was verified. (2) the calculation model of the relationship between stress and curvature is established containing a magnet force of the film material theory, axisymmetric and non axisymmetric and Stoney theoretical framework of the relationship and distinction is discussed. The results show that the films containing magnets stress theoretical model of force and curvature are difficult to degradation in the theory of Stoney model based on the mismatch strain. Based on the theoretical model, developed a set of observation window (diameter 50mm), cryocooler cooling (minimum 30K), controllable continuous change temperature (precision 0.1K) and excitation device (including external magnetic field precision 0.1mT) optical testing system, the method of coherent gradient sensing (CGS) is extended to low temperature, magnetic field and complex environment, in order to achieve a superconducting thin film material at The cooling process of curvature measurement and magnetization process. Through the improved method, the obtained superconducting thin film of pulsed magnetic field on the evolution characteristics of stress distribution and time, provides a reference for the application of safety analysis of superconducting films in pulsed magnetic field environment. (3) involved in the development of extremely low temperature, electricity. Magnetic force, environment field superconducting material characteristic test instrument, is responsible for the design of an optical focusing technology, solves the microobjective during cooling deformation caused by the difficulty in focusing differential pressure and low temperature materials produced by vacuum. At the same time, this paper proposes an adaptive calibration method for luminance - magnetic field, successfully solved this problem of lighting calibration under non-uniform magnetic field. On this basis, the YBCO coated conductor was carried out two typical experiments. First, study on the effect of tensile strain on the critical state of stability. The super conduction material Zero Field cooling to the superconducting state, the applied field of the formation of critical stable state at its edge. The tensile strain gradually increased to 0.6% after the local flux in the mixed state region began to move. With further increase the nucleation strain, local flux from the mixed state area to the Meisner region in Meissner region through, until completely destroyed. The experimental results show that the magnetic penetration depth to meet the exponential strain, and the penetration velocity magnitude is between 1um/s and 1mm/s. Second, the current self field superconducting tapes when tensile strain induced damage and quench related laws. Superconducting zero field cooling to the superconducting state, a constant current is applied to 100A the tensile strain increases gradually, to 0.62%, the flux began to move, with the further increase of strain, the flux to Meisner through, and finally the whole rapid quench.

【学位授予单位】：兰州大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM26

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