超导临界电流测量方法与原理

超导材料的临界电流特性是材料最主要的特性之一,总结了在工程测量中临界电流的定义与判别方法;简要概括了目前5种超导临界电流的测量方法与原理;讨论了各种方法的适用范围、测量条件、测量参量、测量结果以及测量精度和测量过程能得到的材料的其它信息;把几种测量方法作了总结对比,为选择超导材料电流测量方案提供参考。     

等温DSC法研究聚醚胺与环氧树脂固化反应动力学

为了给环氧树脂(DGEBA)/聚醚胺(T403)的实际固化工艺提供指导,在等温条件下采用差示扫描量热法(DSC)对该体系固化过程进行了研究。运用Kenny图像分析法得到了动力学参数,建立了kamal动力学模型;在考虑扩散影响的基础上,多次运用非线性拟合法得到了扩散系数(C)和临界固化度(αc),进一步建立了带扩散控制的动力学模型。结果表明,总反应级数为2.04～2.40,且随固化温度升高而下降。固化反应的两个速率常数都随温度升高而增大,对应的表观活化能分别为42.99和54.23kJ/mol。研究发现不带扩散控制的动力学模型可以较好地描述固化过程的前期阶段,而带扩散控制的动力学模型则可以更好地描述固化全过程。随着固化温度升高,αc增大,扩散影响减小,而带扩散控制的动力学模型与实验结果符合得越好。固化过程属三分子反应,具有明显的自催化特征。     

PbBi/SiO多层交迭膜的制备和分析及其超导性质

以交替的超导/绝缘薄膜作为模型系统。用真空蒸发方法制备了样品并对其层状结构用俄歇谱仪作了检测。低温测试装置具有可控制的温度和强度与方向可调的磁场。测量了超导转变温度及临界电流与温度、磁场的关系。实验结果与钉扎理论的处理很好地一致。     

德国发布新闻公报:硫化氢创下超导临界温度最高纪录

<正>德国马克斯·普朗克协会化学研究所日前发布新闻公报说,其研究人员发现,高压下的硫化氢会在-70℃时失去对电流的阻碍能力,超导临界温度的最高纪录由此被刷新。超导体在一定低温条件下会出现电阻为零的现象。使超导体电阻为零的温度,叫做超导临界温度。此前的纪录是铜氧化物超导材料的超导临界温度最高,其中一种材料在高压下的超导临界温度     

固化条件对丝印 RFID 天线导电性能的影响

目的为了优化丝网印刷RFID天线的固化条件。方法通过正交实验对固化时间和固化温度进行探讨和分析,并运用隧道势垒模型对天线电阻的温度特性进行解释。分析不同的固化时间和固化温度组合对RFID天线导电性能的影响。结果随着固化时间的增加和固化温度的增大,天线电阻都是先减小后增大。结论固化时间为20 min,固化温度为150℃时,RFID天线的线条清晰,边缘平滑,无粘连,天线的平均电阻值最小,导电性能最佳。     

日本NIMS实现临界电流流经铁系超导体

日本物质和材料研究机构（NIMS）超导材料研究中心开发出Fe（Se,Te）系超导线材的简易制作方法,并成功地使超导临界电流流经该线材。临界电流流经铁系超导线在世界尚属首次。     

固化工艺对食品罐内涂双酚A分配系数的影响

目的研究食品罐内涂膜的固化工艺对涂膜中双酚A迁移分配系数的影响。方法在单因素实验的基础上,采用响应面分析法对固化工艺参数进行优化分析,使得双酚A的分配系数最大。结果三因素对迁移物双酚A分配系数的影响主次顺序为涂膜量固化温度固化时间,其中固化温度和涂膜量对双酚A迁移的影响极为显著(P0.0001),且固化温度与固化时间之间,涂膜量与固化时间之间的交互作用极为显著(P0.0001)。在固化温度为200℃,涂膜量为12 g/m~2,固化时间为12 min条件下,双酚A迁移的分配系数最大,为5993.02。结论最佳工艺条件下得到的分配系数与实验值较为接近,说明该响应面得到的工艺参数准确可靠,确保了BPA食品罐的安全性。     

限流器用第二代超导带材的电阻和冲击特性实验研究

为了评估用于电阻型超导限流器的第二代超导带的电阻和大电流冲击特性,实验研究了两种不同厚度的超导带的常温电阻和在100 ms交流大电流冲击下的电流和温升的关系。结果表明,厚带比薄带的耐受冲击电流性能好,但是常温电阻较小。限流器设计时,需在冲击性能和经济性两者之间做出平衡。     

Ba-Y-Cu-O系陶瓷厚膜材料

本文报导采用典型的微电子学厚膜工艺即丝网印刷法,制备Ba-Y-Cu-O系的陶瓷厚膜超导材料,研究了不同热处理温度及时间对厚膜材料性能的影响。实验证明,陶瓷超导材料的厚膜工艺设备简单,适合于大规模生产。用这种方法制备的厚膜超导材料已具有较高的临界超导转变温度:T_c(mid)=80K,T_c(ρ=0)=72.1K,而且工艺稳定,重复性好。     

封闭条件下胶接单搭接头固化过程的实验与数值模拟

汽车板胶粘件外部环境的封闭条件对胶接接头的固化情况影响很大。文中对封闭条件下单搭胶接接头的固化过程进行了实验研究,找出了钢板单搭胶接接头搭接区域温度以及胶粘剂固化度随固化时间的变化规律。为了预测封闭单搭接头固化过程中胶层的固化度变化规律,根据热传导以及固化动力学理论对其固化过程进行三维数值建模,利用实验对模型计算结果进行了验证,通过数值计算发现,固化过程开始时,接头升温速度较慢、且接头整体温度分布不均匀,搭接区域温度较低、两端温度较高,随着固化时间延长,接头升温速率加快,而接头总体温度分布越来越均匀。     

A study of the microscopic deformation behavior of Nb3Sn composite superconducting tape using the acoustic emission technique

Nb₃Sn-based composite superconducting tapes have been widely used because of their excellent properties such as high critical current density, low AC loss and high critical temperature. However, one of the disadvantages of Nb₃Sn-based composite superconducting tape is that the Nb₃Sn compound often exhibits multiple cracking owing to its intrinsic brittleness when subjected to mechanical loading such as bending, winding, and operation. Such cracking eventually causes severe degradation of the critical current density. Therefore, it is very important to understand the microscopic deformation behavior of Nb₃Sn-based composite superconducting tape under mechanical loading.In this study, the microscopic deformation behavior and the fracture mechanism of Nb₃Sn-based composite superconducting tape were investigated using acoustic emission (AE) technique at room temperature. The tensile behavior of Nb₃Sn-based composite superconducting tape was analyzed using the AE parameters including amplitude, duration time, and event count, which are representative of various deformation parameters such as elasticity, yielding, and cracking. The results show that the AE technique is very effective for evaluating the deformation behavior of Nb₃Sn-based composite superconducting tape.     

HTS Joint Resistance for High-Field Magnets: Experiment and Temperature-Dependent Modeling

Journal of Superconductivity and Novel Magnetism - Benefiting from the high critical temperature and high critical current, the second-generation high-temperature superconducting (HTS) tape is...     

Detecting and describing the inhomogeneity of critical current in practical long HTS tapes using contact-free method

The nondestructive and contact-free apparatus for measuring local critical current of long high temperature superconducting (HTS) tapes is presented. The local critical current of tape is acquired by using Hall probe array sensor to measure the remanent field after exposed to dc external magnetic field since the critical current is proportional to remanent field based on Bean critical state model. A detailed experiment on multifilamentary Bi2223/Ag tape is made to validate reproducibility, reliability, resolution, nondestructiveness and usefulness for manufacturer and user of tapes. The parameter COV (coefficient of critical current variation) is suggested for quantitatively describing the inhomogeneity and quality of practical long HTS tape based on Gaussian statistical analysis. The developed apparatus can detect HTS tape at velocity of 100 m/h with resolution smaller than 3 mm in liquid nitrogen.     

Research on resistance characteristics of YBCO tape under short-time DC large current impact

Research of the resistance characteristics of YBCO tape under short-time DC large current impact is the foundation of the developing DC superconducting fault current limiter (SFCL) for voltage source converter-based high voltage direct current system (VSC-HVDC), which is one of the valid approaches to solve the problems of renewable energy integration. SFCL can limit DC short-circuit and enhance the interrupting capabilities of DC circuit breakers. In this paper, under short-time DC large current impacts, the resistance features of naked tape of YBCO tape are studied to find the resistance – temperature change rule and the maximum impact current. The influence of insulation for the resistance – temperature characteristics of YBCO tape is studied by comparison tests with naked tape and insulating tape in 77 K. The influence of operating temperature on the tape is also studied under subcooled liquid nitrogen condition. For the current impact security of YBCO tape, the critical current degradation and top temperature are analyzed and worked as judgment standards. The testing results is helpful for in developing SFCL in VSC-HVDC.     

Characteristics of critical current of superconducting solenoid wound with the stacked tape

The high-T_c superconducting (HTS) magnet is an important element for developing HTS power equipments such as the dc reactor of the inductive type superconducting fault current limiter (SFCL). In order to use the HTS magnet for the large-scale power system, its critical current needs to be high enough. Generally, the double pancake HTS magnet has the severe decrease in the critical current because of magnetic field perpendicular to the tape surface. To fabricate a high critical current magnet, we wound a solenoid with the stacked tape. In this paper, the characteristics of the critical current of the HTS solenoid wound with the stacked tape were investigated. The results of this research can be used as the background data for the design of the large-scale HTS magnet.     

Magnetoresistance,Irreversibility Fields,and Critical Currents of Superconducting 2G Tape

The magnetoresistance, irreversibility fields, and critical current density were studied for a commercial 2G tape at the two relative orientations of magnetic field and superconductor plane. The critical temperatures of this tape of T _{c50 %} = 91.5 K and T _c0 = 90 K and the width of superconducting transition of ΔT = 1.5 K were obtained. The widths of the transition from the normal to the superconducting state do not increase at the applied magnetic field up to 90 kOe and do not depend on the orientation of the magnetic field with respect to the tape plane. The irreversibility field values were obtained and successfully fitted as a function of temperature using the formula: \(H_{\text {irr}} =H_{\text {irr0}} \left ({1-\frac {T}{T_{\text {c0}} }} \right )^{n}\). The irreversibility fields show an anisotropy, and at the liquid nitrogen temperature, they reach H _irr = 430 kOe and H _irr = 106 kOe for the parallel and perpendicular directions, respectively. The anisotropy ratio amounts to γ = 4 at 77 K and is small in comparison with other high-temperature superconducting materials. The critical current density of this tape was found to be of the order of 10⁶ A cm^?2 at 77 K in the self-magnetic field.     

Development of Bi-2223 HTS tape and its application to coil and current leads

We are developing Bi-2223/Ag tapes with a high engineering critical current density by optimizing the powder-in-tube process and are studying its application to coil and current leads. We have fabricated 250 m-long tape and investigated optimized processing conditions to enhance engineering critical current density. More bubbling was found when the tape was heat-treated with a higher heating rate. Different kinds of superconducting joints were fabricated with multi-filamentary Bi-2223/Ag tapes, and 58% of retained I_c was achieved using the insertion of Bi-2223 core between two exposed tapes. Current decay property of the persistent mode HTS coil was investigated. Rapid current decay was observed when the operating current is in a flux-flow range. We could successfully fabricate a low heat leak type HTS current lead with Bi-2223/Ag–Au tapes by employing a stepped geometry. Using this lead, safe operation of 2 kA current transport was confirmed.     

Performance improvement and optimization of a high-temperature superconducting coil having different transport current portions by employing persistent current mode

To improve the performance of a high-temperature superconducting (HTS) coil, it is important to improve its transport current performance. In general, the critical current and n-value of an HTS (Bi-2223/Ag) tape depend on the applied magnetic fields and the angle between the magnetic field and the tape under a constant temperature. The critical currents in the coil edge of the tapes are particularly low because of the distribution of the magnetic fields. However, the critical currents in the central portion remain high. A large amount of current can be supplied to the central portion and the coil performance will improve by supplying different currents between these areas. In this study, I propose an HTS coil in which the coil edge and central portion are isolated for each excitation. Namely, I employ the characteristics of the persistent current mode. The analysis of varying regions of current separation confirmed an optimum current separation. This optimized coil improves the central magnetic field by 21% and the stored energy by 50% compared to those of a normal rectangular coil with an HTS tape of the same length.     

Electromagnetic optimization design of a HTS magnet using the improved hybrid genetic algorithm

The genetic algorithm (GA) is an efficient method in the optimization of superconducting magnets, but there are some limitations of the GA applied to practice design of superconducting magnet, such as poor local search ability, premature convergence, etc. An improved hybrid genetic algorithm is developed by combination of the sequential quadratic programming (SQP). A high temperature superconducting (HTS) magnet by Bi-2223/Ag tape is designed through the improved hybrid GA. A new configuration of the HTS magnet which can reduce the winding volume and become more convenient to construct is suggested with consideration of the constraints, such as central magnetic filed, critical current characteristic, storage energy, and so on.     

Analysis of Current and Magnetic Distributions in REBCO Superconducting Coated Conductors in Self- and External Fields

The influence of a self-field on the critical current density J _c for a REBCO superconducting tape is presented in this paper. The distributions of the current density and magnetic field are analyzed in the tape under three kinds of conditions, i.e., applying an external magnetic field only, applying a transport current only, and applying a transport current together with an external magnetic field. In the analysis, the two-dimensional Poisson equation for the vector potential is employed. For the convenience of calculation, that the dependence of critical current versus the perpendicular and parallel fields tested from experiment is substituted for the traditional Kim-type or Bean model. The results show that the distributions of the current density and magnetic field in the REBCO tape change for the different frequencies and amplitudes of the transport current I _a and applied magnetic field B _a.