High-temperature Superconducting Materials Research Articles

Transmittance properties in a magnetized cold plasma-superconductor periodic multilayer.

This study theoretically investigates the transmittance properties of a one-dimensional photonic crystal containing magnetized cold plasma and high-temperature superconductor materials. The cutoff frequency, as a function of the magnetic field, electron density of the plasma layer, and temperature, will be investigated. The results illustrate that the temperature, electron density, and variations of the magnetic field affect the cutoff frequency. In addition, the shift trend in the cutoff frequency proves to be dependent on the polarization due to the presence of polarization-dependent magnetized cold plasma. Moreover, in temperature-dependent transmittance, weak oscillation and intensity can be seen at higher temperatures, which is in sharp contrast to low-temperature superconductor-dielectric structures. The proposed structure could certainly provide helpful information for the design of new types of antennas, reflectors, and high-pass filters at microwave frequency.

High-Tc Step-Edge Josephson Junction Arrays: Comparison of Simulated and Experimental Voltage Responses

With the recent development of multijunction superconducting quantum interference device (SQUID) arrays and superconducting quantum interference filters (SQIFs) using high-temperature superconducting (HTS) materials, it has become increasingly desirable to accurately model HTS devices to enable the optimization of the design for enhanced performance before fabrication. Initially, to develop our simulation capability for HTS devices, we have been working with a commercial software package to fit the data obtained from the characterization of two HTS devices. The models were iteratively adjusted by increasing the number of parameters taken into account, including the aspect ratio of the SQUID loop and the bias injection point. These models were developed for devices fabricated using YBCO step-edge junctions formed on MgO substrates. It was found that the biasing mechanism affects the SQIF voltage response to applied magnetic fields. This has implications for the design of larger arrays.

Nondestructive Analysis of Bi2212 Bulk Superconducting Ceramics in the C-Axis Direction

The use of superconductors of high critical temperatures in applied superconductivity leads to higher operation temperatures and economy of cryogenic fluids. High temperature superconductor materials exhibits limited transport properties due to grain boundary weak-links and anisotropy on the critical currents. The texturing development in these superconductors decreases in an efficient way the number of high-angle grain boundaries, increasing the values of the critical current densities. Several quantitative analysis methods have been developed to study the morphologic and topologic characteristics improving our understanding of structural parameters. In this work the grain size distribution characterization of Bi2Sr2CaCu2O8+δ Bi2212 superconductor bulk samples heat treated under the influence of an external applied magnetic field of 5T was carried out using a processing technique and analysis of images. The analyzed images were obtained by SEM in the c axis direction. All samples showed similar microstructures on both cases, but with the use of an external applied magnetic field during the heat treatments the average grain size decreased.

Electromechanical energy conversion in a system with a bulk high-temperature superconductor. Part 2. Device operation analysis

The operation of a linear electromechanical vibration device with a part made of a high-temperature superconducting (HTS) material is analyzed. Converter models considered in the first part of this paper [1] are used in the calculations. The parameters of the model of HTS material properties are determined by comparison of the data obtained by calculations and by experimental investigations of force interactions in the laboratory device model. Functions of flux linkage and current force in the coil and permanent magnet movements are calculated for a macroscopic model based on analysis of the electromagnetic field. The calculation results of the operation parameters of the electromechanical converter are shown in the form of amplitude-frequency characteristics of the current in the coil, the permanent magnet movement amplitude, and electrical and mechanical power. Dependences of powers, efficiency, and current phase on the active mechanical load on the resonant frequency are determined. The obtained characteristics are compared with simulation data of a similar converter without the HTS element. It is concluded that the HTS elements significantly change the parameters of the conversion of electrical energy into mechanical energy. It is shown that the electromechanical converters with bulk HTS elements can be more efficient than converters of traditional design.

Conceptual Design Improvement of a Toroidal Field Coil for EU DEMO Using High-Temperature Superconductors

In the frame of the preconceptual design of the next-generation fusion power plant (EU DEMO), the PROCESS systems code is used for nearly 20 years, in which the main reactor components (e.g., plasma, blanket, and magnets) are integrated in a unique computational algorithm and simulated by means of rather simplified mathematical models (e.g., steady-state and zero-dimensional models). In this paper, the boundaries given by the PROCESS code for the toroidal field coil (TFC) of EU DEMO are used as a starting point for the design of a TFC winding pack, using the high-temperature superconductor (HTS) material REBCO as alternative to Nb3Sn. As the DEMO system code parameters are under continuous adjustment, the PROCESS outcome of the July 2012 version is used. This defines the cable space area, the winding pack current density, and the total current in one TFC to generate the required magnetic field on the plasma axis. Based on this and as an extension of the work, the electromagnetic, structural mechanics, cooling, and thermohydraulic properties of an HTS-TFC are presented, and parameters such as operation current, magnetic field and Lorentz forces, operation temperature, structural requirements, cooling, and quench performance are calculated. It is shown that HTS material can be used for the TFC of EU DEMO. At present, the design is made at an operation temperature T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">op</sub> = 4.5 K, allowing adaptation to higher temperatures if the material properties shall improve in the future.

Electromechanical energy conversion in a system with a bulk high-temperature superconductor. Part 1. Mathematical simulation of processes

Features of energy conversion in the linear electromechanical vibration device with an element made of high-temperature superconducting (HTS) material are considered. A disk-shaped permanent magnet with axial magnetization moves inside a fixed circular coil, and a ceramic HTS element, also disk-shaped, is fixed at a distance from the permanent magnet. All converter elements are arranged coaxially. The HTS element transitions into a superconducting state in the magnetic field of the permanent magnet. The purpose of the investigation is to find the effect of the HTS element effect on the static and dynamic parameters of the converter by comparing the operation of the device with the HTS element and without it. Mathematical models are developed for the calculation of dynamic characteristics of the device in the Matlab/Simulink software environment for electrical and mechanical subsystems. The connection between the subsystems is defined by functions of flux linkage of the coil and the electromagnetic force, which are obtained by the analysis of the electromagnetic field by the method of spatial integral equations taking into account HTS material properties. A combined model of HTS material properties is proposed with two sources of magnetic fields (magnetization and current density), which is more universal than current only models.

Toward 20T magnetic resonance for human brain studies: opportunities for discovery and neuroscience rationale.

An initiative to design and build magnetic resonance imaging (MRI) and spectroscopy (MRS) instruments at 14T and beyond to 20T has been underway since 2012. This initiative has been supported by 22 interested participants from the USA and Europe, of which 15 are authors of this review. Advances in high temperature superconductor materials, advances in cryocooling engineering, prospects for non-persistent mode stable magnets, and experiences gained from large-bore, high-field magnet engineering for the nuclear fusion endeavors support the feasibility of a human brain MRI and MRS system with 1ppm homogeneity over at least a 16-cm diameter volume and a bore size of 68cm. Twelve neuroscience opportunities are presented as well as an analysis of the biophysical and physiological effects to be investigated before exposing human subjects to the high fields of 14T and beyond.

MODEL OF MAGNETIC HYSTERESIS PROPERTIES OF MATERIALS IN THE APPLICATION OF A CONSTANT AND VARIABLE MAGNETIC FIELDS

The paper analyzes the modification of the Jiles-Atherton vector model of magnetic hysteresis of materials which is recommended to use in the case of application constant and variable magnetic fields with small amplitude. Such conditions occur in a number of electromechanical energy converters, magnetic suspension, with a magnetic nondestructive inspection. The method is applicable to other models of the vector of hysteresis. It is shown that even for materials with isotropic properties the linearized equations describe the hysteresis process of induced magnetic anisotropy. The findings apply to ferromagnetic materials, and can also be used to describe the hysteresis properties of high-temperature superconducting materials.

Superconductor-Semiconductor Metamaterial Photonic Crystals

We constructed theoretically one-dimensional photonic crystal (1DPC) by using a semiconductor metamaterial in the near-infrared range(NIR) which is composed of Al-doped Z n O(A Z O) and Z n O. The construction of this photonic crystal (PC) is based on a high-temperature superconductor material with the semiconductor metamaterial as constituent layers for this PC. The electromagnetic interactions with this periodic structure are investigated using the transfer matrix method (TMM) in the NIR range. The investigation shows that the reflectance spectra are depending on some parameters of the periodic structure such as the thicknesses of the constituent layers, temperature, and the angle of incidence.

Normal-State Optical Features Study of Nd123 and Gd1212 HTSC Materials for Photonics and Metamaterials Fabrication

YBCO-like Nd123 and Gd1212 superconductors in the normal state, in the visible and infrared regime, have been analyzed in this work. Superconductors, particularly high-temperature superconductors (HTSCs), hold indeed a great interest in the highly innovative research field of metamaterials and photonics with important applications. Indeed nanostructured devices suffer from increasing resistivity with frequency in metals, and superconducting materials provide a viable route to approach this problem. Moreover, HTSCs are plasmonic materials at nonzero temperature, and their features, not available in conventional materials, make them very attractive for metamaterials use. In particular, we investigate Nd123, for its high T c , and Gd1212, for the coexistence, in its unitary cell, of magnetic order and superconductivity. Samples were extracted from top-seeded melt-textured growth bulk pellets and bars. Fourier transform infrared spectroscopy analysis, performed in the far-infrared, shows articulated peak structures with k <; k min and a plateau for higher k, allowing for Nd123 and Gd1212 pseudogap measurement. Raman spectroscopy and microscopy provided a structural mapping of our Nd123 samples, allowing for distinguishing the superconducting matrix from nonsuperconducting phase inclusions (precipitates) and providing an instrument to discriminate among optical responses of the different compounds.

Hysteresis Losses Analysis in 2G HTS Cables

The Russian Scientific R&D Cable Institute is involved in many projects on R&D high-temperature superconducting (HTS) power cables including those made of modern second generation (2G) HTS wires. Evaluation of ac losses and methods for the reduction of the ac losses are important in the design of the cables. A fine experimental technique has been developed and implemented to measure ac losses in representative cable models with a length of ~5 m. However, only calculation can provide ac loss prediction in cases when it could be difficult to make measurements. Thus, we need a comprehensive simulation model to calculate ac losses. In HTS cables made of 2G wires, the main ac loss is a hysteresis loss, which only numerical simulation can predict for full-size 2G cables. We develop a finite-element method model to solve the electromagnetic problem for the calculation of ac losses. The model takes into account the strong nonlinear resistivity of the HTS materials, the hysteresis behavior of the magnetic substrate, the nonuniformity of critical current density across the tapes of the cable, and the possible ferromagnetism of a substrate. The model also takes into account any geometrical aspect of the 2G HTS cables. The details of the model and comparisons of calculations with our measurements of the ac losses are presented.

Monte Carlo Design Space Exploration of Superconducting Wind Generator Using MgB2 and YBCO Conductors

Considering the global outcry over climate change and the need for increased penetration of clean forms of energy in ever-increasing aspects of the modern economic sphere, wind power installations, particularly offshore, are expected to rise in the next decades. However, the main obstacle to this trend will be represented by the high installation costs. In order to reduce these costs, the wind turbines generators require to be manufactured to yield higher torque density with lower material input in terms of weight. One way to pursue this requirement is to employ high-temperature superconductor (HTS) technology for the rotor windings and/or the stator windings, making it possible to design cheaper generators for 10-MW applications. This work considers the impact of HTS conductors in wind turbine generators to complement material research work at the University of Houston HTS material research work. Four topologies of generators were investigated: two partially superconducting generators employing YBCO and MgB2 as conductor for the rotor windings and two fully superconducting generators employing MgB2. The electromagnetic physics governing the machine was simulated by finite-element analysis software, i.e., FlexPDE; then, a numerical analysis of thousands of models was realized by Python. An exploration of the results was carried out making use of an optimum criterion considering a simple aggregation of the generator mass active, the copper, ac stator windings losses, and the amount of superconductor needed. Trends of these optimization criteria with reference to design parameters are shown in detailed plots. According to the specific aims of the designer, the investigation provided interesting clues regarding, among others, the number of pair of poles and the amount of superconductor employed characterizing the best models.

Fabrication of hybrid thin film structures from HTS and CMR materials

We present the preparation of bilayers from high-temperature superconductors (HTS) and half-metallic ferromagnetic (FM) manganite with a colossal magnetoresistance (CMR). We used YBa2Cu3O7-x (YBCO) and Tl2Ba2CaCu2O8 (TBCCO) thin films as a HTS material and La0.67Sr0.33MnO3 (LSMO) film as a CMR material. In the case of YBCO/LSMO, we prepared FM/HTS heterostructure for studying the spin-polarized current injection effect on the electrical properties of the YBCO strip in dc or low-frequency regimes and on the microwave characteristics of the strip. For the first time, we report the preparation of a TBCCO/LSMO bilayer. In some applications, the TBCCO offers better parameters (higher working temperature, lower surface resistance, lower 1/f noise) than YBCO.

Design Optimization of Round Strands Made by Twisted Stacks of HTS Tapes

A twisted stack of high-temperature superconducting (HTS) tapes soldered into copper profiles was used as a strand in the fabrication of the 60-kA/12-T HTS cable prototype at the Center for Research in Plasma Physics (CRPP). Considering the strand in general as a modular element for the high-current cables, design parameters of the strand need to be optimized in order to best fulfill requirements of appropriate application field. During the development program of the HTS fusion cable at CRPP, influence of the design parameters on the strand's performance was obtained as input data for the optimization process. In this paper, we summarize the results of the twisting, bending, and transverse pressure tests on strands of various tapes and profile's geometries. Finite-element model for the transverse pressure test was developed, validated with the test results, and used for the design proposals. Effect of the stack aspect ratio, tape properties, and anisotropy, as well as selection of HTS material for the strand, will be discussed.

Toward an Optimum Design of Large-Scale HTS Synchronous Generator for Wind Turbine Applications

In this paper, a thorough analysis is carried out to obtain an optimum design for a 10-MW-class high-temperature superconducting (HTS) synchronous generator for wind conversion systems. Different design challenges are studied, and a multiobjective function, which includes mass, cost, volume, and operating characteristics of the generator, has been considered. An improved analytical hierarchy process technique as a multiobjective decision-making algorithm is used to optimize the proposed objective function, and thereby, optimum dimension parameters of the generator are achieved. It is deduced that the generator total cost, particularly the HTS material price, has considerable influence on the optimum structure of the generator, which should be considered in the design procedure. This investigation suggested a precise study to obtain an optimum structure of the large-scale HTS synchronous generator for wind turbine applications.

First-principles prediction of MgB2-like NaBC: A more promising high-temperature superconducting material than LiBC

Abstract Crystal structure, lattice dynamics, and superconducting properties for sodium borocarbides NaB1+xC1−x are investigated with first-principles calculations. Based on crystal structure analysis by particle swarm optimization methodology, NaBC is predicted to crystallize in the layered P 6 3 / m m c crystal structure as LiBC. However, it is different from LiBC, in that Na atoms are effectively ionized, with no longitudinal covalence exist between Na and B–C layers, just as in the case of MgB2. Therefore, Na1−xBC is more similar to MgB2 than Li1−xBC as a potential high-temperature superconductor. Further more, we suggest that the slight hole doping of NaBC through partial substitution of C by B atoms can also produce cause superconductivity. The phonon spectra for NaBC and NaB1.1C0.9 are obtained within the virtual-crystal approximation treatment. There is a remarkable softening of the in-plane B–C bond-stretching modes for NaB1.1C0.9 in certain regions of the Brillouin zone, while other phonon bands show no obvious softening behavior. This conspicuous softening of the in-plane B–C bond-stretching modes indicates a strong electron–phonon coupling for them. The obtained total electron–phonon coupling strength λ for NaB1.1C0.9 is 0.73, and superconducting transition temperature T C is predicted to be 35 K ( μ * = 0.1 ). This indicates that NaB1+xC1−x is potentially high-temperature superconducting and hole doping of NaBC could produce high-temperature superconductivity. In addition, we conjecture that, to design a MgB2-like high T C superconducting material, the longitudinal covalent bonds between the metal cations and graphite-like layers need be excluded.

Slow In-Plane Magnetoresistance Oscillations in Multiband Quasi-Two-Dimensional Metals

Slow oscillations (SlO) of magnetoresistance is a convenient tool to measure electronic structure parameters in quasi-two-dimensional metals. We study the possibility to apply this method to multi-band conductors, e.g. to iron-based high-temperature superconducting materials. We show that SlO can be used to measure the interlayer transfer integral in multi-band conductors similar to single-band metals. In addition, the SlO allow to measure and compare the effective masses or the electron scattering rates in various bands.

Investigation of stabilizer material properties used with REBCO coated conductor tapes for the application in a 20 kA High Temperature Superconductor Current Lead

In almost all fusion and accelerator experiments presently in operation or under construction, current leads (CLs), which feed the magnets, use high-temperature superconducting (HTS) materials to reduce the total cooling power consumption of the He refrigerator. These CLs carry currents in the range of 10–68 kA. The Karlsruhe Institute of Technology successfully designed, built, and tested the 70-kA demonstrator CL for the ITER magnets, which was subsequently followed by the 18.2-kA HTS CLs for the Wendelstein 7-X stellarator and the 20-kA and 26-kA HTS CLs for the JT-60SA tokamak. All these CLs use the first-generation HTS material BSCCO. The HTS part of the CL is now the focus of a new development aiming at a substitution of BSCCO by the next-generation HTS material RE BCO. To limit the heat load to the cryostat, the stabilizer material of the RE BCO coated tapes requires a low thermal conductivity. In addition, stabilizers with a sufficiently high electrical conductivity are mandatory in order to protect the CL in case of a quench of the RE BCO tapes. A part of this new development is therefore a detailed material property investigation of RE BCO coated conductor single tapes with a low thermal conductivity, in order to define a suitable conductor for a 20-kA CL and to create a database for the subsequent technical optimization process. This paper summarizes the measurement results of the thermal conductivity, electric resistivity, and specific heat capacity for RE BCO single tapes with a low heat leakage. The results are analyzed with regard to earlier investigations of the BSCCO tapes used in the Wendelstein CLs serving as a reference for a future RE BCO CL.

Small grains: a key to high-field applications of granular Ba-122 superconductors?

The grain boundaries (GBs) of high-temperature superconductors (HTSs) intrinsically limit the maximum achievable inter-grain current density (), when the misalignment between the crystallographic axes of adjacent grains exceeds a certain value. A prominent effect resulting from large-angle GBs is a hysteresis of between the increasing and decreasing field branches. Here, we investigate this feature for K- and Co-doped Ba-122 polycrystalline bulks with systematically varied grain size and find that the widely accepted explanation for this effect—the return field of the grains—fails. We use large-area scanning Hall-probe microscopy to distinguish from the intra-granular current density () in order to clarify their interactions. Measurements on Ba-122 bulks reveal that a large results from a small as well as small grains. An extended version of the model proposed by Svistunov and D’yachenko is successfully applied to quantitatively evaluate this behavior. The excellent agreement between the model and experiments suggests that the GBs limit the macroscopic current in all of the samples and that the inter-grain coupling is governed by Josephson tunneling. The predictions of the model are promising in view of realizing high-field HTS magnets. Our main result is that the field dependence of the of an untextured wire can be significantly reduced by reducing the grain size, which results in much higher currents at high magnetic fields. This result is not limited to the investigated iron-based materials and is therefore of interest in the context of other HTS materials.

Design and performance of a 1 MW-5 s high temperature superconductor magnetic energy storage system

The feasibility of a 1 MW-5 s superconducting magnetic energy storage (SMES) system based on state-of-the-art high-temperature superconductor (HTS) materials is investigated in detail. Both YBCO coated conductors and MgB2 are considered. A procedure for the electromagnetic design of the coil is introduced and the final layout is arrived at and compared for the two materials. The choice of the inductance of the coil is carried out as part of the design procedure. Both low-field (3 T) and high-field (8 T) designs are considered for the YBCO. AC losses during a complete charge/discharge cycle at full power are estimated and the cooling power needed for continuous operation is derived. The power conditioning system and control algorithms needed to carry out various operations are discussed in detail. Performances of the SMES system during voltage sag compensation, load leveling and power factor correction are investigated by means of numerical simulation.