高温超导导线I_c-B特性的测量

测量了高温超导导线Bi-2223/Ag的临界电流值与外加磁场的依赖性关系.实验结果表明:超导线材的临界电流不仅与磁场大小有关,而且还与外磁场的方向有关.外磁场越大,临界电流值越小;Bi-2223/Ag呈扁带状,临界电流对磁场的依赖性呈现各向异性.该实验与高温超导材料临界温度测量实验结合为高温超导电性能综合测试实验,为学生自主研究提供了拓展空间.     

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.     

Modelling stability in superconducting cables

Stability is one of the key issues in the design of a superconductor, and indeed deserves much attention in the magnet design and analysis. Stability-oriented design procedures and calculations involve the detailed knowledge of the response of the cable to thermal, fluid dynamic and electric transient phenomena that are difficult to tackle analytically in cables. This has justified a significant numerical modelling effort in the field. This paper reviews basic stability models and presents selected advances in the methods developed and results obtained. A unified, semi-continuum model is proposed for stability analysis of cables. The time scales of relevance during stability transients are identified and analysed.     

High-T c superconducting magnetic bearings for rotation-based devices

Summary A Modified-Melt-Powder-Melt-Growth (MMPMG) technique has been developed for the preparation of melt-textured Y-Ba−Cu−O pellets. To test their performances, the samples were characterized with respect to their microstructure, pinning strength and interaction force with permanent magnets. A superconducting magnetic bearing was built and integrated in a levitating flywheel system for energy storage. Paper presented at the “VII Congresso SATT?, Torino, 4–7 October 1994. Under a Fondazione Confalonieri grant.     

Multistable current states in high-temperature superconducting composites

Conditions for current instabilities that arise in high-temperature superconducting composites with essentially nonlinear dependences of the critical current densities and resistivity on the temperature and magnetic induction have been studied. The analysis has been conducted in terms of zero-dimensional models, which has made it possible to formulate general physical mechanisms behind the formation of currents states in superconducting composites according to the external magnetic field induction, cooling conditions, and the properties of the superconductor and cladding. The possible existence of current and temperature stable steps, as well as stable steps of the electric field strength, in the absence of the superconducting–normal transition, has been demonstrated. Reasons for instabilities under multistable current states have been discussed.     

AC loss in a high-temperature superconducting coil

In a typical superconducting coil made of BSCCO/Ag tape, both amplitude and direction of the magnetic field determine the critical current, resistive voltage and AC loss. The distribution of the magnetic field along and across the superconducting tape in a coil is rather complex. This gives rise to the question: how accurate can one predict the critical current, V–I characteristic and AC loss of the AC coil from results of short sample measurements? To answer this question, we have measured and compared the characteristics of a short sample and a small coil employing 14 m of the same tape at 77 K. The comparison is performed as follows. First, a short sample is characterised with regard to the field dependence of the critical current, V–I characteristic and the AC loss. Second, the distribution of the magnetic field along the tape in a coil is accurately calculated. From the data, the voltage along the tape and the loss of the tape in the coil are found. Finally, the resistive voltage and the AC loss of the complete coil are calculated and compared to measured AC losses in the frequency range of 0 to 160 Hz, typical for power applications.     

高温超导磁悬浮轴承选择与设计

新型无摩擦高速高温超导磁悬浮轴承是高温超导磁悬浮技术最有潜力的应用之一,具有巨大的工业应用前景。文中分析比较了轴向型和径向型两种高温超导磁悬浮轴承的特点,并利用轴向型高温超导磁悬浮轴承结构简单、制作容易的优点,设计制作了一台双轴向型高温超导磁悬浮轴承样机。实验结果显示,上、下两高温超导磁悬浮轴承完全实现了2.4kg转轴的稳定悬浮及无接触旋转运行,目前受驱动电机转速限制,最高试验转速为3000 rpm。在稳定运行的基础上,该轴承样机将最终用于高温超导飞轮储能系统的原理演示。     

低温绝缘的高温超导电缆失超检测研究

高温超导电缆在电力系统中运行是发展趋势,若超导电缆本身故障或电力系统故障时都会对其产生重要影响。文中在理论分析低温绝缘的高温超导电缆在短路故障情况下屏蔽层电流与导体层电流相位、幅值的关系基础上,提出了针对低温绝的缘高温超导电缆的失超检测新方法——基于幅值差值检测和相位差值变化率检测,并通过仿真软件PSCAD/EMTDC分析了电力系统发生各种短路故障时高温超导电缆的失超特性,从而验证了这两种检测方法的可行性。     

铜电流引线组的二元化改造

传统的铜电流引线因为在低温区的漏热过大,需要改造成漏热量低的高温超导电流引线。本设计主要针对一对200A和两对80A铜电流引线。通过计算得出了高温超导电流引线的最佳长横比,以及结构在不同低温区的收缩率,并用对电流引线组改造前后做了漏热的分析对比。结果表明,改造后的电流引线组4.5K温区的漏热量降低到未改造前的3.18%,大大降低了系统液氦温区热负荷,降低了运行成本。     

高温超导磁悬浮轴承动态测试平台

为了研究高温超导磁悬浮轴承样机的动态旋转特性,介绍了由振动分析仪、转速计和位移传感器组成的动态测试平台。该测试平台不仅可以测试高温超导磁悬浮轴承的共振频率、刚度和阻尼系数等基本动态参数,而且可以实时测试旋转轴承的转速和振动偏移等运行参数。通过脉冲激励实验和自由衰减实验证实测试实验数据真实可靠。该平台的搭建将为本小组在轴对称式高温超导磁悬浮技术(轴承、飞轮等)的应用研究和开发奠定基础。     

A high-temperature superconducting filter with controllable transmission zero

This paper presents a novel microstrip feedline structure to introduce an extra and controllable transmission zero(TZ)with high rejection for a narrowband filter. This structure loads a reconfigurable capacitor at the end of the input feedline without changing the main structure of the filter. The capacitor is recognized by a 2-bit inter-digital capacitor array. The asymmetrical microstrip feedline structure is suitable for multiple-pole filter designs. A low-loss six-pole high-temperature superconducting bandpass filter with a reconfigurable TZ is designed and fabricated. The center frequency of the filter is 5.22 GHz with TZ at the lower stopband. The TZ can be tuned among four different states. The out-of-band rejection at the TZ frequency is higher than 90 d B, and the insertion loss is lower than 0.92 d B. The measured results are consistent with the simulations.     

Tuning the resonance in high-temperature superconducting terahertz metamaterials

In this Letter, we present resonance properties in terahertz metamaterials consisting of a split-ring resonator array made from high-temperature superconducting films. By varying the temperature, we observe efficient metamaterial resonance switching and frequency tuning. The results are well reproduced by numerical simulations of metamaterial resonance using the experimentally measured complex conductivity of the superconducting film. We develop a theoretical model that explains the tuning features, which takes into account the resistive resonance damping and additional split-ring inductance contributed from both the real and imaginary parts of the temperature-dependent complex conductivity. The theoretical model further predicts more efficient resonance tuning in metamaterials consisting of a thinner superconducting split-ring resonator array, which are also verified in subsequent experiments.     

UHF波段宽阻带高温超导滤波器设计

在分析电容加载的微带线谐振器模型的基础上,提出一种基于叉指电容、块状电容和弓形折线电感的新颖谐振器,其第一谐频位于5.6f_0外。利用该谐振器,在28mm×12mm×0.5mm的YBCO/MgO高温超导基片上设计制作了4节超导滤波器,中心频率为500MHz,相对带宽为1%。测试结果表明该滤波器具有优异性能,带内插损小于0.3d B,反射损耗优于15d B,通带与5.6f_0处寄生通带之间的抑制度大于75d B,实现了宽阻带和高抑制度的带外抑制特性。     

Local measurements of magnetic characteristics of high-temperature superconducting films

A new experimental technique for measuring magnetic characteristics of high-temperature superconducting (HTS) films is described. The measurement system includes a laser providing for local measurements. The measured magnetic characteristics of the HTS films are of scientific and practical interest.     

基于高温超导双晶结的约瑟夫森效应观测实验

基于YBa2Cu3O7-δ高温超导双晶结,组建了约瑟夫森效应测试装置.利用此装置观察了直流和交流约瑟夫森效应,并测量了约瑟夫森结的临界电流和夏皮罗台阶.     

Analysis of current ramp for a high-temperature superconducting magnet

In this paper, an equivalent electrical circuit for response of a high-temperature superconductor (HTS) system for arbitrary time varying transport current is considered and as well as an analysis of the generated resistance losses is given. Also, for the pancake coil made with superconducting Bi-2223/AgMg tape, hysteresis behavior on the voltage-current curve is examined as a function of the current rate during ramp up and down at liquid nitrogen temperature. Behavior of voltage versus current is in good agreement with considered theory.