A 3-D finite element formulation for calculating Meissner currentsin superconductors

A three-dimensional (3-D) finite element formulation for calculating Meissner currents in superconductors is presented. The authors have chosen a magnetic vector potential formulation, which also enables them to simulate ferromagnetic shielding. The equations are written so that the problem can be solved by the use of a conjugate gradient algorithm without preconditioning. Numerical results on normal-superconductor junctions and on superconducting lines are compared with analytical solutions     

Theoretical studies and experimental results of a SMES used in apulsed current supply

A superconducting magnet energy storage (SMES) can be used as a pulsed power supply. A superconducting coil stores energy without electrical losses and this energy can be recovered through a second wire on which the charge (electromagnetic launcher, for example) is linked. The design of such an apparatus needs to solve simultaneously thermal, magnetic, and electric equations. We proposed a three-dimensional finite difference method to solve these coupled problems. This tool enables us to describe resistive zones of expansion in thick coils during a quench and to predict the duration and the efficiency of the discharge. Moreover, it indicates if the coil is prevented from an excessive temperature increase. Then, a probative device is described and experimental results are compared with theoretical ones     

Finite-element calculation of Meissner currents in multiplyconnected superconductors

A three-dimensional (3D) finite-element formulation for calculating Meissner currents in multiply connected superconductors is presented. The fluxoid quantization condition is ensured as simply as possible. The problem is formulated so that we have to solve two systems of equations by the use of a conjugate gradient algorithm without preconditioning. Meissner currents and magnetic-flux density are numerically evaluated in a superconducting tube and around a vortex. These results are compared with analytical solutions     

A superconducting magnet system for free-electron cyclotron maser

A superconducting magnet system for free-electron cyclotron maser is developed. This system includes a main superconducting magnet, a gradient superconducting magnet, a normal magnet, a cryostat and some accessories. The designed magnet system has the advantages of having a small size, high stable magnetic field and suitable field profile. It is very suitable for a 4mm wavelength free-electron cyclotron maser. The design and some experimental results are given.     

Scattering parameter and bit error rate characterization of hightemperature superconducting coplanar transmission lines

We report the gigahertz experimental results of time and frequency performance on YBCO high temperature superconductor (HTS) and gold coplanar transmission lines. An on-wafer direct probing measurement system was used to collect data at cryogenic temperatures on both YBCO and gold coplanar lines. The insertion loss of the 6-cm lines at a frequency of 3.0 GHz was measured to be -0.12 dB for the superconducting line compared to -10.7 dB for the gold line at 80 K. Error rate and eye-diagram measurements were performed on the packaged lines and show the correlation between the insertion loss of the line and the attenuation of a Pseudo Random Bit Sequence (PBRS). The superconducting line measured at 77 K had a BER rate of less than 10^-11 at a data rate of 3 Gb/s. The measured eye height was 350 mV for the YBCO compared to 100 mV for a gold line at 3 Gb/s and a temperature of 77 K for the packaged 6-cm lines     

Physical Modeling of Hot-Electron Superconducting Single-Photon Detectors

In this paper, we treat the incident photons as an electromagnetic plane wave and simulate the wave power coupling to the the hot-electron superconducting single-photon detector to investigate its connection with the experimental system quantum efficiency over different wavelengths. Then we propose a lumped equivalent circuit model based on the kinetic inductance variation induced by the incident photon stream when the serpentine superconducting thin-film nano-wire is dc-biased close to its critical current. The computed output voltage matches experimental results for both amplitude and frequency.     

Alternative Designs of High-Temperature Superconducting Synchronous Generators

This paper discusses the different possible designs of both cored and coreless superconducting synchronous generators using high-temperature superconducting (HTS) tapes, with particular reference to demonstrators built at the University of Southampton using BiSCCO conductors. An overview of the electromagnetic, thermal, and mechanical issues is provided, the advantages and drawbacks of particular designs are highlighted, the need for compromises is explained, and practical solutions are offered. The scalability of results obtained from small demonstrators is considered.      

Superconductive magnetoelectric field-effect transistor

A transistor-like three-terminal superconducting device-the superconductive magnetoelectric field-effect transistor (SMET)-is described. The SMET represents a field-controlled Josephson device with its control based on the magnetoelectric effect. The device is characterized by a very high input-output isolation because the input is strictly voltage-controlled. As such, it may be useful for interconnecting voltage-controlled semiconductor electronics with current-controlled superconducting devices. The design considerations are reviewed, and preliminary experimental results are presented. Possible other practical applications are also discussed     

The study of the target emissivity and detection using a superconducting detector in the submillimeter wave region

This paper researches mainly the radiation characteristics of the target and detecting techniques by superconducting detector in the submillimeter wave(SMMW) region. The calculation of transition wavelength(TW) between Planck and Rayleigh-Jeans is given out. The experiment of detecting different targets is finished by use of superconducting detector possessing high performances. Through the experiments in paper we can select and determine the wave bands of SMMW detecting and imaging system. The many novel theoretical analyses and experimental results are expressed in Figs and tables of the paper. Finally, a part of calculating results and experimental datum detected by a superconducting detector in SMMW regions are given in this paper.     

Magneto-optical visualization of magnetic processes in superconducting strip with the application of magnetic fields and currents

The magneto-optical imaging (MOI) technique is widely employed to characterize the magnetic properties of superconductors and other magnetic materials because it can easily show the variation of flux density over a plane with relatively high resolution. In this paper, flux profiles visualized by the MOI technique will be presented for different experimental conditions. The sample investigated is a high-temperature superconducting single strip. Three cases are investigated: 1) application of external currents; 2) application of external magnetic fields; and 3) simultaneous application of external magnetic field and current. The behavior of complicated vortex penetration into the samples for different conditions will be discussed in detail. The magnetic flux profiles are calculated taking into account the sample thickness, as well as the interval between the sample and the MOI indicator film. The calculated and the experimental results are compared and discussed.     

Analytical model of superconducting to normal transition of bulk high Tc superconductor BSCCO-2212

A comprehensive theoretical expression for the superconducting-to-normal transition of high-temperature superconducting (HTS) materials is derived. The electric field and resistivity of bulk melt-cast processed BSCCO-2212 are derived from the superconducting, flux creep, flux flow, and resistive properties of high critical temperature superconductors (HTS). An asymptotic function is used to model the Bean and Ohmic limits of the E(B,T,J) characteristics. Comparison is made with the experimental results of Elschner et al. The new model may be used in simulating the operation of HTS power equipment, and may be applicable to other HTS materials.     

Newly developed millimeter-sized superconducting linear actuatorwith superconducting slider

A millimeter-sized superconducting linear actuator has been developed. The actuator consists of a superconducting slider, a stator, amplifiers, and a personal computer. Exciting currents for six-phase excitation are applied to the electromagnets of the stator. The experimental results show that the superconducting slider moves over the stator without any mechanical contacts and that the motion resembles a stepping motor. The stable position for the levitating slider depends on the magnetic field produced by the electromagnets. The maximum speed of the slider is more than 10 mm/s     

Slotline ring resonator test method for high-Tcsuperconducting films

A novel method of testing high-T_c superconducting (HTS) films by means of a slotline ring-like resonator is presented. This method does not require any metallic contact with the HTS films and ensures that the tests have quick turnaround times. Small samples can be tested very easily. The resonator circuit used has been studied analytically using Sonnet Inc.'s em software. The parameters of the HTS films are obtained by fitting the theoretical results to the experimental ones. YBa₂Cu₃O_7-δ films on LaAlO₃ have been tested and the theoretical and experimental results are presented and compared. The results match very well. This method is useful for quick screening HTS films since no patterning of the film is required     

基于FDTD的约瑟夫森结与超导传输线协同分析方法

为实现高性能处理器,超导RSFQ（快速单磁通量子）电路被提出.该电路主要由超导约瑟夫森结和超导无源传输线组成,对其建模分析是超导RSFQ电路设计的基础.本文提出了基于FDTD（时域有限差分）的约瑟夫森结与超导传输线的协同分析方法.该方法采用FDTD数值方法求解超导传输线的电报方程.在超导传输线与约瑟夫森结交界处的非线性边界条件上,采用了Newton-Raphson迭代算法.数值结果表明,本文提出的约瑟夫森结和超导传输线的协同分析方法与WRspice仿真软件相比具有相同精度,且运算效率显著提高.     

Picosecond applications of Josephson junctions

The behavior of simple superconducting circuits in the picosecond regime is described in a comprehensive way, with primary emphasis being given to the step function and pulse responses of these circuits. Topics receiving detailed discussion include Josephson-junction modeling with both the microscopic and shunted-junction models. Limitations of the shunted-junction model are explored by comparing it with experimental results and with the microscopic model. An approximate evaluation is given of the important dynamical properties of junctions made with the dominant fabrication technology (Pb-alloy systems), as a function of tunneling barrier thickness. Rounding out the device aspects of the discussion, we describe in detail the properties of superconducting microstrip transmission lines, with an emphasis on their high-speed behavior. Turning to simple circuits we review experimental results on the measurement of picosecond regime transient signals. The concept of turn-on delay is analyzed anew, providing simplified and extended results. Details of concepts for pulse height and pulsewidth measurements are explored, leading to the conclusion that the time resolution of superconducting circuits is limited to approximately the period of one plasma oscillation. With present Pb-alloy fabrication technology this limit is 2 ps.     

High-Temperature Superconducting Loss-Free Delay Network for High-Power Pulse

In this paper, a high-temperature superconducting (HTS) loss-free delay network for high-power pulses is performed. Based on the voltage and current pulse experiments carried out at 300 and 77 K, experimental results demonstrate that, under the matched resistive load condition, compared with a normal conducting lossy delay network, the HTS loss-free delay network can effectively reduce the amplitude attenuation of voltage pulses and the front-edge distortion of current pulses.     

Superconducting millimeter-wave E-plane filters

The authors report on the measured performance of a three-pole E-plane filter constructed from high-T_c superconducting bulk materials at 34.5 GHz. Experimental results are presented for the insertion loss and return loss of the filter at 77 K. The problems associated with the use of bulk materials at the millimeter-wave range are addressed. Other possible superconducting waveguide filter configurations are proposed. While the experimental results are taken at low input power level, the current distribution inside the filter structure is calculated, and the power handling capability of the superconducting filter is discussed     

超导磁体失超检测中电压隔离校正电路的设计

采用有源功率检测法,设计和制作了超导混合储能磁体能量储存系统的失超检测中的电压隔离校正装置。该装置用于隔离超导线圈的干扰信号,以及消除串联线圈电感分量,是混合磁体失超检测中的重要环节。通过搭建高温超导线圈的实验装置,在高温超导储能磁体上进行失超检测的实验研究,得出了电压矫正前后的线圈电压波形,验证了本实验装置可行性与合理性。     

Magnetically enhanced terahertz response of Josephson junctions

We investigate the magnetic field effects on the terahertz (THz) response of grain boundary Josephson junctions. First, we show some experimental results of the THz response enhanced by a dc magnetic field. The experimental results and device configuration indicate that the THz RF magnetic field plays a role in enhancing the response. Second, we numerically simulate the current-voltage characteristics and obtain the power dependence of Shapiro steps. Since the junctions are wide compared to the inferred Josephson penetration depth, multiple current paths within a junction are possible and superconducting quantum interference device (SQUID) models should be used. Two kinds of SQUID models are used: an RF-current drive model and an RF-field activation model. Shapiro step enhancement by a dc magnetic field can be reproduced with the use of the RF-field activation model. Finally, we discuss step-height dependence on SQUID parameters as well as give a qualitative explanation for the different predictions of two SQUID models