Bi-2223/Ag高温超导带临界电流各向异性的实验测量及分析

本文介绍了Bi-2223/Ag高温超导带临界电流各向异性的实验测量方法及原理,指出了在不同磁场方向(与超导带面夹角)下,Bi-2223/Ag带临界电流随直流背景磁场的变化规律以及实验应注意的问题.Bi-2223/Ag带材的各向异性决定了其临界电流对垂直于带材表面的磁场非常敏感,这是该带材在高温超导磁体等强电应用方面的不利因素.     

传导冷却高温超导磁体的电磁分析

本文对高温超导双饼线圈的绕制、测试和结果进行了讨论和分析,在此基础之上对传导冷却高温超导磁体进行了电磁分析,通过对6到21个双饼线圈组成的磁体的各种参数进行计算,得到了一系列变化曲线,从中可以看到各个参数的变化趋势,以便有效设计高温超导磁体.     

Bi-2223/Ag高温超导带材临界电流实验研究

为了研究磁场、温度对Bi-2223/Ag带材超导性能的影响,建立了一套测量带材临界电流的实验装置,该装置能够提供稳定的背景磁场,控温精度最高可达±20m K,在零场、控温(77.3K)条件下样品的临界电流测量值与带材给定参数基本吻合,表明该装置测量精度满足要求;文中将高温超导带材放在特制控温罩中,使用He气冷技术和温控系统调节样品温度(4.2—80K),测量了在0—12T背场下高温超导带材的临界电流,并系统地分析了Bi-2223/Ag带材临界电流对温度和磁场的依赖关系。     

高温超导带材失超传播特性实验研究

采用测量多个电压节点顺序失超的方式,测量了在液氮浸泡和有包裹材料情况下不锈钢加强Bi-2223/Ag和YBCO涂层导体高温超导带材样品的失超传播速率。根据实验结果,Bi-2223/Ag高温超导带的失超传播速率约为2 cm/s,YBCO带材的失超传播速率约为0.4 cm/s,均远远低于低温超导材料的相应数值。对这一现象的原因进行了简要分析,并根据高温超导带材的这一特点,提出了在高温超导电力应用中需特别注意的问题。     

传导冷却高温超导磁体的电磁分析

本文对高温超导双饼线圈的绕制、测试和结果进行了讨论和分析，在此基础之上对传导冷却高温超导磁体进行了电磁分析，通过对6到21个双饼线圈组成的磁体的各种参数进行计算，得到了一系列变化曲线，从中可以看到各个参数的变化趋势，以便有效设计高温超导磁体。     

利用高压热处理技术提高Bi-2223/Ag高温超导带材临界电流

提高临界电流密度(Jc)对促进Bi-2223/Ag高温超导带材的应用有着重要意义.在常压热处理条件下所制备的带材中存在大量的裂纹、孔洞和第二相颗粒等,这些因素都会对带材的超导连接性能产生破坏作用.我们成功建立了一套可用氧气氛的热等静压设备,工作气压和温度可同时达到15MPa和850°C.通过引入裂纹愈合热处理过程,我们成功对带材进行了高压热处理,所得样品中第二相颗粒和裂纹数量大幅度降低,77K、自场下的临界电流相比常压热处理样品提高了20%左右.     

一种新的高温超导磁体电磁结构优化设计方法

本文阐述了用于高温超导磁体电磁结构优化设计的一种新方法,与一般优化方法不同之处在于其不用定义磁体的初始结构形状,采用该方法可以得到满足规格和性能要求的较佳磁体结构.通过此方法优化设计了一个中心磁场为3T的Bi系高温超导磁体,其设计结果与满足同样要求且经过优化的单螺管高温超导磁体的设计结果作了对比,由结果表明该方法具有很好的优化效果.     

基于混合算法的传导冷却高温超导磁体的优化设计

遗传算法是一种行之有效的优化算法,具有很强的自适应性、鲁棒性和全局搜索能力,但其亦存在着未成熟收敛及进化缓慢等问题.为提高遗传算法的寻优性能并考虑到磁体工程实际问题,本文对遗传算法作了改进,并与局部优化算法序列二次规划算法相结合形成一种优势互补的混合算法,并将其应用于3.2T传导冷却Bi系高温超导磁体的优化设计中,取得了良好效果.     

基于混合算法的传导冷却高温超导磁体的优化设计

遗传算法是一种行之有效的优化算法，具有很强的自适应性、鲁棒性和全局搜索能力，但其亦存在着未成熟收敛及进化缓慢等问题．为提高遗传算法的寻优性能并考虑到磁体工程实际问题,本文对遗传算法作了改进，并与局部优化算法——序列二次规划算法相结合形成一种优势互补的混合算法，并将其应用于3．2T传导冷却Bi系高温超导磁体的优化设计中，取得了良好效果．     

用于脉冲电源的高温超导脉冲变压器模型及其参数影响分析

高温超导脉冲变压器用于能量存储以及电流脉冲放大,是电感储能型脉冲电源的重要设备。为了合理地设计高温超导脉冲变压器线圈的几何参数,满足脉冲功率系统体积小型化和储能密集化的发展趋势,本文选择了同轴饼式线圈叠加结构的脉冲变压器模型,利用有限元仿真软件Ansoft Maxwell进行建模仿真,分析了几何参数对高温超导脉冲变压器原边超导线圈的临界电流密度、储能容量、线圈中超导带材的受力以及变压器耦合系数的影响。通过对仿真结果的综合分析,得出原边超导线圈的高厚比小于0.3时,小型高温超导脉冲变压器可以获得较高的性能,为脉冲功率技术的基础性实验验证研究提供了一定的理论基础。     

Percolation in inhomogeneous superconducting composite wires

We report the initial results of SQUID voltmeter measurements on Cu-alloy wires which contain elongated μm-scale inclusions of superconducting Nb. Below the transition temperature T_c of the Nb inclusions the wires have a temperature-dependent resistance which can be fit to R ∝ (T - T_cl)^s where s = 1.06 ± 0.04. We develop a simple model employing percolation theory to explain this behavior.     

Gapless excitations in strongly fluctuating superconducting wires

We study the low-temperature tunneling density of states of thin wires where superconductivity is destroyed through quantum phase-slip proliferation. Although this regime is believed to behave as an insulator, we show that for a large temperature range this phase is characterized by a conductivity falling off at most linearly with temperature, and has a gapless excitation spectrum. This novel conducting phase results from electron-electron interaction induced pair breaking. Also, it may help clarify the low-temperature metallic features found in films and wires whose bulk realization is superconducting.     

Localization and delocalization in dirty superconducting wires

We present Fokker-Planck equations that describe transport of heat and spin in dirty unconventional superconducting quantum wires. Four symmetry classes are distinguished, depending on the presence or absence of time-reversal and spin-rotation invariance. In the absence of spin-rotation symmetry, heat transport is anomalous in that the mean conductance decays like 1/sqrt[L] instead of exponentially fast for large enough length L of the wire. The Fokker-Planck equations in the presence of time-reversal symmetry are solved exactly and the mean conductance for quasiparticle transport is calculated for the crossover from the diffusive to the localized regime.     

一款C波段极窄带高温超导滤波器

设计了一款中心频率位于C波段的10阶高温超导滤波器,相对带宽达到0.1%。该滤波器的拓扑结构采用准椭圆函数型,引入了2组CQ结构,分别来改善了滤波器的带边陡度和群时延平坦度,较好解决了寄生耦合对极窄带滤波器的影响。测试结果和仿真结果基本吻合,达到了预期目标。     

Stoichiometric relations in high-temperature superconducting compounds

Applying the Jing and Gonser model for the high-T _c superconductivity based on electron hopping the Stoichiometric connections and appropriate restrictions are given. It is shown that for the compounds of typeA _2–x B _xCuO₄ andAB ₂Cu₃O_9–x, whereA is a trivalent rare-earth ion andB is a divalent alkali earth ion, the superconductivity is realized only if 0T _c superconducting compounds are propounded and considered, too. The optimum compound which contains fluorine atoms should be of the form YBa₂Cu₃F₂O_5.875. All the relations presented find confirmation in experiments.     

Quantum decay of supercurrent in thin superconducting wires

Quantum fluctuations cause a decay of the supercurrent in thin superconducting wires making them resistive even at very low temperatures. We derive a microscopic effective action formalism that goes beyond the usual TDGL approach and study quantum fluctuations of the superconducting order parameter at all temperatures belowT _C . We calculate the quantum phase slip rate in thin superconducting wires, demonstrate the importance of dissipation in a quantum phase slip process, and evaluate the resistanceR(T) of the wire. In very thin wires the effect is well observable, even at zero temperature.     

Pinning-force density of superconducting Bi-2223 tape wires

The pinning-force density and the irreversibility field are measured for Bi-2223 tape wires at various temperatures under the magnetic fields normal and parallel to the c-axis. It is found that the scaling laws of pinning-force density in the low- and high-temperature regions and the temperature dependence of the irreversibility field are formally the same between the two field directions in spite of some anisotropy factor, suggesting that the pinning mechanism is essentially the same for the two field directions. These results are compared with the numerical calculation based on the flux-creep model. The experimental results are well explained by the theory including the anisotropic property.

The pinning potential estimated from the flux-creep theory at 80 K and 1.0 T is of the order of several 10 meV and the factor of the anisotropy is about 1.3. The value of the pinning potential under the magnetic field along the c-axis suggests that the flux lines are strongly connected along this direction. The longitudinal elastic correlation length of the flux lines is of the order of several μm and this supports the hypothesis.

The pinning characteristics of a Bi-2223 tape wire to which the strong pinning centers are successfully introduced are discussed using the flux-creep theory for evaluating the potential of this material for application. The irreversibility field for the direction parallel to the c-axis is estimated to be sufficiently high even at 77.3 K and it is concluded that Bi-2223 has a sufficient potential for application.