Explanation of Pressure Effect for High Temperature Superconductors Using Pressure Dependent Schrodinger Equation and String Theory

A pressure dependent Schrodinger equation is used to find the conditions that lead to superconductivity. When no pressure is exerted, the superconductor resistance vanishes beyond a critical temperature related to the repulsive force potential of the electron gass, where one assuming the electron total energy to be thermal, where applying mechanical pressure destroys Sc when it exceeds a certain critical value. However when the electron total energy is an assumed to be that of the free electron model and that the pressure is thermal and mechanical, the situation is different. The quantum expression for resistance shows that the increase of mechanical pressure increases the critical temperature. Such phenomenon is observed in high temperature cupper group.

High T_c Superconductor Theoretical Models and Electromagnetic Flux Characteristics

High Tc Superconductors （HTS） have special electromagnetic characteristics and phenomena. Effort has been made in order to theoretically understand the appfied HTS superconductivity and HTS behaviors for practical appfications, various theoretical models related to the HTS electromagnetic properties have been developed. The theoretical models and analytic methods are summarized with regard to understanding the HTS magnetic flux characteristic which is one of the most critical issues related to HTS appfications such as for HTS magnetic levitation application.

High Temperature Superconductivity in the Past Twenty Years Part 2——Towards to Practical Applications

After discovering high temperature superconducting materials 20 years ago, the preparation of applicable HTS materials has been pursued along with HTS mechanism and characteristic study. At present, the focus on the applied HTS technology has been moving to the industrial preparations from the laboratory research stage, and the technology has been well verified for practical applications from small to large scales. The fabrication techniques of engineering HTS materials are being industrialized; and various HTS devices are also on the way towards practical applications. This paper provides a comprehensive summary on the applied high temperature superconductivity with regard to various applicable HTS materials, their preparation techniques and charac- terization, and applications in a wide range.

Summary of the First Generation High Temperature Superconducting Wire: Processing, Characterization and Applications

Silver-clad （Bi,Pb）2Sr2Ca2Cu3O10＋x long wires produced by powder-in-tube techniques, which have been recognized as the first generation of the High Temperature Superconducting （HTS） wires, are expected to apply widely especially in strong current applications. In this work, the processing, characterization and application of the silver-clad （Bi,Pb）2Sr2Ca2Cu3Ol0＋x HTS wires are summarized. The HTS wires are fabricated using the combination of powder-in-tube technique, and the resulting wires are fully characterized by the means of chemical analyses, microstructural observation, electrical and magnetic measurements. The relationship among fabrication parameters, chemical and microstructural characteristics, and electrical and magnetic properties are analyzed. Applications of the HTS wires have also been introduced according to their strong current behaviors with various prototype devices made.

High T_c Superconducting Materials for Strong Current Applications:Approach at the First Stage

Strong current and large-scale application is the most important prospect of high Te superconductors （HTS）. Practical HTS samples in various forms have been produced with high critical currents operated at economic cryogenic temperatures. Engineering applications of those HTS materials have been studied with various HTS prototype devices. The applicable HTS materials produced in different forms are verified in this paper with regard to their strong current characterizations, and the HTS applications are summarized along with the HTS prototypes made.

40-meter-long REBCO tapes with critical current over 4,000 A/12 mm at 4.2 K and 13 T by advanced MOCVD

REBa_(2)Cu_(3)O_(7−δ)(REBCO,RE=rare earth)tapes doped with 5%and 15%Zr have been scaled up to lengths more than 40 m in a pilot‐scale advanced metal organic chemical vapor deposition(A‐MOCVD)tool.The precursor compositions used for the long tapes were guided by a study of the influence of(Ba+dopant)/Cu content on the critical current density(Jc)of 5 and 15 mol.%Hf‐and Zr‐added tapes at 4.2 K and 13 T.The 40‐mlong tapes exhibited a critical current(Ic)over 4,000 A/12 mm at 4.2 K and 13 T as well as over 1,400 A/12 mm at 20 K and 20 T.The critical current densities of a 40‐m‐long tape doped with 5%Zr at 4.2 K measured at the National High Magnetic Field Laboratory(NHMFL)were>10 MAcm^(−2)and>5 MAcm^(−2)at 14 T and 30 T,respectively,which are over three times those of commercial REBCO tapes.The infield Jc of 5%Zradded 40‐m‐long tapes was similar to those of previously‐reported high‐performance short samples made with 15%Zr or Hf.These results demonstrate the excellent potential of A‐MOCVD for manufacturing high Ic REBCO tapes for use in ultrahigh‐field magnet applications.

Phase Evolution Study and Optimization of the Heat Treatment Process for High Current Capacity Bi-2223 Tapes

Powder in tube process（PIT） was adopted for the fabrication of single filament Bi-2223 tapes, and a heat treatment process including the first heat treatment（HT1）, intermediate rolling（IR）, and second heat treatment（HT2） was performed. The phase evolution mechanism and microstructure changes during these heat treatment processes were systematically discussed. The influences of HT1 parameters on the phase evolution process of Bi-2223 tapes were discussed. With the optimized HT1 process, a proper Bi-2223 content of about 90% was achieved. HT2 process was also optimized by adding a post annealing process. An obvious increase of current capacity was obtained due to the enhancement of intergrain connections. Single filament Bi-2223 tapes with the critical current of Ic-90 A were fabricated with the optimized sintering process.

Preparation,Microstructure and Properties of Ag-sheathed Bi(Pb)-Sr-Ca-Cu-O Superconductor Tapes

The process to obtain high T(110K)phase quickly,the microstructure and properties of Ag-sheathed Bi(Pb)-Sr-Ca-Cu-O superconductor tapes have been studied.It was found that the formation time of the high T_c phase was greatly shortened by the addition of more Ca and Cu to the nominal composition of Bi(Pb):Sr :Ca:Cu=2:2:2:3 and the adoption of appropriate sintering temperature and cooling rate. Superconductor powder with predominant high T,phase was prepared after a 840 C/50 h treatment.The J of the Ag-sheathed tapes and the magnetic field dependence of Jwere obviously improved by repeatedly pres- sing and sintering.The maximum transport current density at 77K in a zero magnetic field was 12,200 A/cm^2. The magnetic dependence of Jwas summarized as follows:6.450 A/cm^(2)(B⊥1.B∥S.0.1T)1,810 A/cm^2 (B⊥1.B∥S,1T),390 A/cm^2(B⊥1.B∥S,2T)(B:magnetic field.1:electric current.S:surface of tapes).The improvement of Jwas attributed to the formation of the plate-like structure with homogeneous composition distribution and the strong c-axis texture.

Variance of Critical Current Density with Microstructure by a Special Process

A promising method —“powder in tube”technique was used to fabricate Ag-sheathed Bi-2223 superconductive tapes with high critical current density.After a combination processing of pressing and subsequent heat treatment,we obtained tapes with high degree of texture,good compaction and uniform properties.At 77 K in zero field,J_C was higher than 1×10~4 A/cm^2 while the highest J_C was 1.69×10~4 A/cm^2.SEM and XRD was used to detect the tapes texture,and the relationship be- tween J_C and the degree of texture is discussed.In addition,the reason for obstacling the improvement of J_C is also investigated.

MICROSTRUCTURE AND PROPERTIES OF YBaCuO SUPERCONDUCTOR PREPARED BY MTG METHOD

In this study, high-Tc YBaCuO superconductors with high Jc value were prepared using MTG(melting-textured growth) method. These superconductors with high density have Jc value in excess of 1.6×104 A/cm2 (77K, zero field) determined by using a d.c. standard four terminal method with the criterion of lμV/cm. The XRD and fractograph analysis revealed that the texture existed in whole MTG-processed YBaCuO sample which consists of the layered and plate-like grains of matrix phase YBa2Cu3Oy unidirectionally aligned along its (103) planes. The experimental results indicated that the connectivity between superconducting grains has been improved greatly and the weak-link problem has been overcome essentially.

An Inquiry into Two Intriguing Values of the Critical Current Density of Bi-2212

The empirically reported values of the critical current density (jc) of Bi-2212 as 2.4 × 105 (jc1;Sample 1) and 1.0 × 106 A/cm2 (jc2;Sample 2) are intriguing because both of them correspond to the same values of the temperature T = 4.2 K and the applied magnetic field H = 12 × 104 G. This difference is conventionally attributed to such factors—not all of which are quantifiable—as the geometry, dimensions and the nature of dopants and the manners of preparation of the samples which cause their granular structures, grain boundaries, alignment of the grains and so on to differ. Based on the premise that the chemical potential μ subsumes most of these features, given herein is a novel explanation of the said results in terms of the values of μ of the two samples. This paper revisits the problem that was originally addressed in [Malik G.P., Varma V.S. (2020) WJCMP, 10, 53-70] in the more accurate framework of a subsequent paper [Malik G.P., Varma V.S. (2021) JSNM, 34, 1551-1561]. Besides, it distinguishes between the contributions of the electro-electron (e-e) and the hole-hole (h-h) pairs to jc—a feature to which no heed was paid earlier. The essence of our findings is that the jcs of the two samples differ because they are characterized by different values of the primary variables μi and , where is the effective mass of a charge-carrier and me is the free-electron mass and i = 1 and 2 denote Sample 1 and Sample 2, respectively. In the scenario of the charge-carriers being predominantly h-h pairs, the values of these parameters are estimated to be: μ1 ≈ 12.3 meV, η1 ≈ 0.58;μ2 ≈ 22.7 meV, η2 ≈ 0.94. Following from these and similar estimates when the charge-carriers are e-e pairs, given below for each sample are the detailed results for the values of the secondary variables viz. the number density of the charge-carriers and their critical velocity, the number of occupied Landau levels and the magnetic interaction parameter.

REBCO高温超导长带临界电流连续化测量及其均匀性表征

由于具有高临界转变温度(Tc)、高临界电流密度(Jc)和高上临界磁场(Bc2)等优点,第二代高温超导体(REBCO,RE=稀土元素)得到广泛应用,临界电流(Ic)及其沿长度方向均匀性和n-值是重要的关键参数。文章综述了高温超导长带临界电流及其沿长度方向均匀性以及n-值的测量方法,综合比较了各种测量方法的优缺点,并讨论了各种方法的适用范围、测量条件以及测试数据等,旨在为高温超导长带测量方案提供依据,为后续测量标准的制定提供参考。

外界磁场对两种YBCO超导带材临界电流及n值影响分析

为掌握钇钡铜氧(YBCO)高温超导带材在不同种类和大小的外界磁场环境下的基本特性,针对AMSC和Superpower制备的两种不同的YBCO超导带材(超导带材Ⅰ和Ⅱ)在不同磁场强度及角度下的Ic及n值进行实验测量和计算,分析了外界磁场变化对Ic及n值的影响。采用在液氮环境下改变超导带材的外界磁感应强度及角度(0～0.9T,0～90°),在交直流背景磁场下,应用直流超导电源给超导带材加载流并测量带材两端的电压,获得两种YBCO高温超导带材的Ic(1μV/cm)及n值(0.1～1.5μV/cm)。由实验结果可知,虽然两种超导带材的Ic及n值都随外界磁场强度的增大而减小,但是无论是在直流背景磁场还是在交流背景磁场下,带材表面与磁场的夹角对超导带材Ⅰ特性的影响要小于超导带材Ⅱ,超导带材Ⅰ的稳定性要好于超导带材Ⅱ。

连接参数对Bi系(BSCCO)超导带材扩散连接接头性能的影响

采用高温直接加压退火工艺扩散连接61芯B i系高温超导带材。研究了835℃连接温度下接头搭接长度、搭接区窗口的台阶数、保温时间对接头结合界面特征及其超导电性的影响。结果表明,连接参数对接头超导电性Ic影响明显,超导电性低的接头其超导芯结合界面处有未焊合迹象,母材经过835℃扩散连接热循环后超导电性显著降低。

高温环境下的轴承保持架转速非接触测试方法

滚动轴承是发动机、燃气轮机等设备中的重要旋转部件,需要长期工作在高温环境中。为了预防轴承打滑,减少轴承损伤及失效,需要实时获取高温环境下的轴承保持架转速参数。文中提出了一种基于涡流效应的耐高温转速传感器,使用耐高温线绕制传感器探头,通过周期性改变轴承保持架与探头的距离实现保持架转速的测量。搭建高温转速平台进行测试,验证了传感器的可行性,实现了高温时轴承保持架转速的非接触测量。结果表明:在300℃高温环境中,转速传感器的最大非线性误差为0.511%,最大重复性误差为0.771%。

高T_c超导材料YBCO临界温度测量方法

本文讨论了高温超导材料临界温度的测量原理和方法,采用动态法测量了钇钡铜氧(YBCO)超导体材料的电阻—温度特性,文中给出了测量结果并对其进行了讨论分析。

富BaCO_3对YBCO超导样品的超导性能的影响

为提高 1 2 3相高温超导材料的临界电流密度Jc,本文从改变样品的用料配方、革新制备工艺等方面做了一些尝试和研究。在生成约 1 0g1 2 3相超导样品正常配比的基础上 ,分别多加了 5mg到 1 0 0mg不等的BaCO3 ,采用固相反应法制备了超导体块材。通过比较各样品的超导转变温度Tc、超导转变宽度ΔT、临界电流密度Jc、扫描电镜照片和X Ray衍射谱图 ,可以得出 :富BaCO3 1 2 3相超导体的超导转变温度Tc均大于 90K ;ΔT =1～ 3K ;2 0mg的富BaCO3 有利于 1 2 3相的形成 ;一定量富BaCO3 的加入对提高 1 2 3相超导材料的临界电流密度Jc很有利。

Ba源配比对MOCVD法制备YBCO薄膜性能的影响研究

采用单一液相混合源进液及闪蒸的MOCVD系统在LaAlO3(001)单晶基片上制备YBa2Cu3O7-x(YBCO)薄膜,研究混合源中Ba含量对YBCO超导薄膜成分、结构及电流承载能力的影响。结果表明,当Ba含量较小时,YBCO薄膜中易于形成尺寸较小的CuO颗粒;随着Ba含量的增加,薄膜中形成Ba2CuO3晶粒,并且Ba2CuO3晶粒尺寸随Ba含量的增加而逐渐增大。杂质相的含量、尺寸以及与YBCO的晶格匹配程度对YBCO薄膜的双轴取向生长和电流承载能力具有重要影响。当原料摩尔配比Ba/Y=3.9时,成功制备出了具有优异面内面外取向、结构致密的YBCO超导薄膜,77 K下的300 nm厚度薄膜的临界电流密度达到4.0 MA/cm2,该研究结果对于第二代涂层导体的发展具有重要意义。

非均匀高温超导带材对CORC电缆失超特性的影响研究

高温超导CORC(conductor on round core)电缆失超时的热负荷严重威胁了低温系统和电缆本体的安全稳定运行。受微米级超导薄膜制备工艺等的影响,CORC电缆并绕的多根高温超导带材不均匀。为分析不均匀临界电流对CORC电缆失超特性的影响,该文搭建了基于三维TA方程的有限元模型。以降维的带材曲面为求解区域,以等效的电流密度为求解变量,失超模型在同一几何中表达超导和常导两种属性,构建电流和电势两种约束。在导体域建立降维的热模型,用以考虑损耗和传热的影响;在全局建立等效的电路模型,用以控制并联导体的分流。进一步地,耦合模型考虑温度依赖的接头电阻以模拟CORC电缆带材的烧断和电流的突变。结果表明,非均匀高温超导带材影响了电流重分配的动态响应,加快了局部失超的发展过程。

Progress in inhomogeneity of critical current and index n value measurements on HTS tapes using contact-free method

The development of high temperature superconducting(HTS)tapes has recently made great progress,and Bi-based tapes(1 G) and YBCO coated conductor(2 G)are commercially fabricated with practical length.Application of HTS in electric power apparatuses made important achievement,various superconducting devices were demonstrated in grid,laying solid foundation for their commercialization.However,since their intrinsic microscopic defects such as weak-link,granularity,small second phase likely exist,critical current and index n value of the HTS tapes in practical length are impossible homogeneous,which have significant influences on safety,stability and efficiency of the HTS apparatuses.Therefore,critical current and index n value are two important parameters describing inhomogeneity of HTS tapes,thus two important indices for evaluating quality of practical long HTS tapes.This paper focuses on main progresses in inhomogeneity of critical current and index n value measurements on HTS tapes using contact-free methods.The statistical analytical methods evaluating the inhomogeneity of critical current and index n value are suggested.They can provide essential references for design and operation of HTS apparatuses.