基于LabVIEW的高温超导材料特性测试实验

高温超导体临界特性的测量是近代物理实验中最为经典的实验之一,本文通过使用GM制冷机,利用Lab-VIEW虚拟仪器软件和高性能采集卡,改进了传统的测量高温超导材料临界特性的实验装置.本测试系统不仅可以测量高温超导体在不同温度下的临界电流,还可以测量其失超传播特性.该实验对于学生了解超导体特性和培养严谨的科学作风十分有益.     

Bandpass microwave filters based on YBCO high-temperature superconductor films

The experimental characteristics and results of a simulation of four-pole filters based on high-temperature superconductor films fabricated by the Theva firm (Munich) and the Institute for Physics of Microstructures, Russian Academy of Sciences (Nizhnii Novgorod) are presented. The model parameters and surface resistance of the investigated films are determined from the characteristics obtained. For direct measurements of the films’ surface resistance, a disc resonator with a frequency of 10 GHz has been developed at the Institute for Physics of Microstructures.     

Current-carrying element based on second-generation high-temperature superconductor for the magnet system of a fusion neutron source

Application of current-carrying elements (CCEs) made of second-generation high-temperature superconductor (2G HTS) in magnet systems of a fusion neutron source (FNS) and other fusion devices will allow their magnetic field and thermodynamic stability to be increased substantially in comparison with those of low-temperature superconductor (LTS) magnets. For a toroidal magnet of the FNS, a design of a helical (partially transposed) CCE made of 2G HTS is under development with forced-flow cooling by helium gas, a current of 20–30 kA, an operating temperature of 10–20 K, and a magnetic field on the winding of 12–15 T (prospectively ~20 T). Short-sized samples of the helical flexible heavy-current CCE are being fabricated and investigated; a pilot-line unit for production of long-sized CCE pieces is under construction. The applied fabrication technique allows the CCE to be produced which combines a high operating current, thermal and mechanical stability, manufacturability, and low losses in the alternating modes. The possibility of fabricating the CCE with the outer dimensions and values of the operating parameter required for the FNS (and with a significant margin) using already available serial 2G HTS tapes is substantiated. The maximum field of toroidal magnets with CCEs made of 2G HTS will be limited only by mechanical properties of the magnet’s casing and structure, while the thermal stability will be approximately two orders of magnitude higher than that of toroidal magnets with LTS-based CCEs. The helical CCE made of 2G HTS is very promising for fusion and hybrid electric power plants, and its design and technologies of production, as well as the prototype coils made of it for the FNS and other tokamaks, are worth developing now.     

A new concept for a current switch based on a high-temperature superconductor

A new concept for a device for protecting an alternating-current network is offered. It is based on a combination of a superconducting limiter of a short-circuit current and a circuit breaker. A high-temperature superconductor in the form of a pile of plane rings is used as the active element of the limiter. The test results of a model of such a limiter are obtained in the steady-state short-circuit regime. The characteristics of composite silverless materials used for design of the breaker are given.     

Nonlinear interaction of a ferromagnet with a high-temperature superconductor

The interaction of an Abrikosov vertex with a ferromagnetic substrate is taken into account in the model of a layered high-temperature superconductor (HTSC). The magnetization reversal loops are calculated by the Monte Carlo method for various values of the magnetic moment of the substrate and at various temperatures. The nonlinearity of the interaction of the superconductor with the ferromagnet is demonstrated. The magnetization of HTSC films on magnetic and nonmagnetic substrates is measured. It is found that the ferromagnetism of the substrate strongly affects the shape and magnitude of the magnetization of the HTSC-substrate composite. Experimental data are found to correlate with the results of calculations.     

1/f conduction noise in the high-temperature superconductor Bi-Sr-Ca-Cu-O system

Conduction noise was investigated in the normal state of the 2212 phase of the Bi-Sr-Ca-Cu-O system for polycrystals, highly oriented thin films, and single crystals. It was found that large noise with 1/f spectrum in this material is generated as a bulk effect. The magnitude of the noise power is 7–10 orders of magnitude larger than in normal metals even in single crystals. Several possible origins are discussed.     

Theoretical studies of high-temperature multilayer thermal insulations using radiation scaling

The objective of the paper is to model combined heat transfer in multilayer thermal insulations (MTI) for application to high-temperature fuel cells operating at temperatures higher than 650°C. Therefore, solid and gas conduction as well as radiation had to be considered. For conductive heat transfer, referenced models are subjected to sensitivity and plausibility analyses. For modelling the radiation heat transfer, a radiation scaling model reported in literature was adapted to the present problem and compared with experimental data. Finally, internal heat transfer phenomena and a numerical optimisation of MTI are discussed.     

Q factor of megahertz LC circuits based on thin films of YBaCuO high-temperature superconductor

High-frequency properties of resonant structures based on thin films of YBa₂Cu₃O_7–δ high-temperature superconductor are studied experimentally in the frequency range 30–100 MHz. The structures planar induction coils with a self-capacitance fabricated on neodymium gallate and lanthanum aluminate substrates. The unloaded Q factor of the circuits exceeds 2 × 10⁵ at 77 K and 40 MHz. Possible loss mechanisms that determine the Q factor of the superconducting resonant structures in the megahertz range are considered.     

Local magnetooptical study of magnetic structures in high-temperature superconducting composites

The results from magnetooptical investigations of the remagnitization processes in composite film structures based on high-temperature superconductors in the temperature range of 4 to 80 K are presented. It is shown that the remagnetization of structures is due to the formation and propagation of wave of magnetic flux annihilation (areas with zero magnetic induction). The relationship between the penetration depth of annihilation front and the external magnetic field at different ambient temperatures, and the temperature dependence of the rate of motion of the front of magnetic flux annihilation, are found. The experimental data qualitatively fit the results from numerical calculations performed using the Monte Carlo method.     

Intermodulation in a microwave resonator with a high-temperature superconductor

Intermodulation, or the generation of a combination-frequency signal, is studied theoretically in the case where the nonlinearity is provided by a high-temperature superconductor placed in a microwave resonator. A general formula that relates the power of an intermodulation signal to the electromagnetic performance of the resonator, the physical parameters of the superconductor, and the intensity of pump waves is derived. A parameter that characterizes the nonlinearity is evaluated from data available from the literature. The potentialities of various resonators for the microwave characterization of the nonlinearities in high-temperature superconductors are assessed.     

Lateral magnetic stiffness under different parameters in a high-temperature superconductor levitation system

Magnetic stiffness determines the stability of a high-temperature superconductor(HTS) magnetic levitation system.The quantitative properties of the physical and geometrical parameters that affect the stiffness of HTS levitation systems should be identified for improving the stiffness by some effective methods. The magnetic stiffness is directly related to the first-order derivative of the magnetic force with respect to the corresponding displacement, which indicates that the effects of the parameters on the stiffness should be different from the relationships between the forces and the same parameters.In this paper, we study the influences of some physical and geometrical parameters, including the strength of the external magnetic field(B0) produced by a rectangular permanent magnet(PM), critical current density(Jc), the PM-to-HTS area ratio(α), and thickness ratio(β), on the lateral stiffness by using a numerical approach under zero-field cooling(ZFC)and field cooling(FC) conditions. In the first and second passes of the PM, the lateral stiffness at most of lateral positions essentially increases with B0 increasing and decreases with β increasing in ZFC and FC. The largest lateral stiffness at every lateral position is almost produced by the minimum value of Jc, which is obviously different from the lateral force–Jc relation. The α-dependent lateral stiffness changes with some parameters, which include the cooling conditions of the bulk HTS, lateral displacement, and movement history of the PM. These findings can provide some suggestions for improving the lateral stiffness of the HTS levitation system.     

Magnetostriction of the high-temperature non-cuprate superconductor BaBiKO

Measurements of the magnetostriction of the isotropic high-temperature superconductor Ba_0.66K_0.34BiO₃ revealed an effect of the order of 10⁻⁶ which exceeds that for conventional superconductors but is not as high as the giant magnetostriction of cuprate high-temperature superconductors. A thermodynamic analysis of the results enables comparison with the results of numerical calculations of effects induced by magnetic flux pinning. Fiz. Tverd. Tela (St. Petersburg) 40, 1199–1203 (July 1998)     

Mechanisms of dissipation in a Josephson medium based on a high-temperature superconductor in a magnetic field

This paper reports on the results of an investigation into the influence of magnetic fields (0–60 kOe) on the temperature dependences of the electrical resistance R(T) of the Y_3/4Lu_1/4Ba₂Cu₃O₇ + CuO composites. The structure of these composites is considered to be a network of tunnel-type Josephson junctions in which a nonsuperconducting component (CuO) forms boundaries (barriers) between high-temperature superconducting crystallites. The temperature dependence R(T) of the composites has two steps characteristic of granular superconductors: (i) an abrupt change in the electrical resistance at the critical temperature of high-temperature superconducting crystallites and (ii) a smooth transition to the superconducting state under the influence of the boundaries between the crystallites. The experimental dependences R(T) are analyzed within the Ambegaokar-Halperin model of thermal fluctuations in Josephson junctions and the flux creep model. An increase in the magnetic field leads to a crossover from the Ambegaokar-Halperin mechanism to the flux creep mechanism. The temperature dependences R(T) in the range of weak magnetic fields (from 0 to 10² Oe) are adequately described by the relationship following from the Ambegaokar-Halperin model. In the range of strong magnetic fields (from 10³ to 6 × 10⁴ Oe), the dissipation obeys the Arrhenius law R ～ exp(?U(H)/T)], which is characteristic of the flux creep model with a temperature-independent pinning energy U(H). The effective Josephson coupling energies and the pinning energies corresponding to the Ambegaokar-Halperin and flux creep mechanisms are determined.     

Transport properties of high-temperature superconductor + semiconductor composites with different carrier concentration

Results are presented of an experimental study of the temperature dependence of the electrical resistivity ρ(T), critical current density J _c(T), and current-voltage characteristics of polycrystalline composites based on the high-temperature superconductor Y_3/4Lu_1/4Ba₂Cu₃O₇ and copper oxide with different lithium doping levels. The experimental temperature dependence of the critical current of composites with varying volume content of the semiconductor ingredient and varying charge carrier concentration are found to be in qualitative agreement with theory which takes account of Andreev reflection of the carriers at the S-Sm and Sm-S surfaces of the S-Sm-S Josephson junction (where S is the superconductor and Sm is the semiconductor). Fiz. Tverd. Tela (St. Petersburg) 39, 829–834 (May 1997) Deceased     

Aberrations of magnetooptical system of SALO recirculator

The influence of spatial and chromatic aberrations on the parameters of the 730 MeV beam extracted from a SALO recirculator is studied using numerical simulation. The influence of fringing fields and the heterogeneity of the guide field of dipole magnets on the beam parameters at the extraction point is studied for different orders and types of aberrations. Estimates of the contributions of the different types of aberrations to the extracted beam emittance are presented.     

The effect of superstructural ordering on the properties of high-temperature oxide superconductor systems

The effect of superstructural ordering in the oxygen sublattice (in addition to the influence of the antiferromagnetic interaction of copper ions) on the electron and phonon characteristics of oxide high-temperature superconductor (HTSC) systems has been studied. Taking into account this ordering effect, it is possible to explain a wide range of experimental data, including doping-induced changes in shape of the Fermi surface, features of the phonon spectra, the existence of stripes, the presence of a pseudogap and its coexistence with the superconducting gap, and some peculiarities in the phase diagrams of HTSCs.