High-temperature Superconducting Properties Research Articles

Fast evaluation of the critical current of high-temperature superconducting coils based on the integral method

The need for energy is growing as civilization develops. Superconductors have various benefits over regular conductors, including a high current-carrying density and nearly no resistance. Therefore, the objective that scientists continue to seek is the use of superconductors to replace traditional conductors in order to satisfy the demand for energy. As a key part of the superconducting electrical system, the critical current is one of the key properties of high-temperature superconducting (HTS) coils. Scholars have created a variety of numerical simulation models to estimate the performance of HTS coils. However, the extremely nonlinear E–J power law relationship that characterizes the voltage–current relationship in superconducting materials necessitates numerous iterative refinements during the coil design stage, which is time-consuming from the perspective of computing efficiency. Consequently, it is essential to increase computational efficiency. In this study, the critical current of HTS coils was calculated using the J model (integral method with the current density J as the state solution variable), and it was proved to be an efficient research method. The accuracy of the method is verified by comparing with the H model and the experimental measurement results of the critical current of the HTS coil. Moreover, compared with the reference finite element simulation model, this model has a speed advantage of at least four times, which is a good choice, especially, for HTS circular coils with large turns.

Exploring the Effect of the Number of Hydrogen Atoms on the Properties of Lanthanide Hydrides by DMFT

Lanthanide hydrogen-rich materials have long been considered as one of the candidates with high-temperature superconducting properties in condensed matter physics, and have been a popular topic of research. Attempts to investigate the effects of different compositions of lanthanide hydrogen-rich materials are ongoing, with predictions and experimental studies in recent years showing that substances such as LaH10, CeH9, and LaH16 exhibit extremely high superconducting temperatures between 150–250 GPa. In particular, researchers have noted that, in those materials, a rise in the f orbit character at the Fermi level combined with the presence of hydrogen vibration modes at the same low energy scale will lead to an increase in the superconducting transition temperature. Here, we further elaborate on the effect of the ratios of lanthanide to hydrogen in these substances with the aim of bringing more clarity to the study of superhydrides in these extreme cases by comparing a variety of lanthanide hydrogen-rich materials with different ratios using the dynamical mean-field theory (DMFT) method, and provide ideas for later structural predictions and material property studies.

Exciton and fermion-pair condensation at non-zero temperature

A thermodynamic study of a many-particle two-level system with the SU(2) ⊗ SU(2)-symmetry interaction in the particle–particle and particle–hole channels is carried out. Using the symmetry of the system, its free energy and phase diagram are calculated. It is demonstrated that the superconducting (particle–particle) and excitonic (particle–hole) condensates are both formed in the considered system which undergoes two phase transitions. The calculated phase diagram represents qualitatively the phase diagram typical for materials with the high-temperature superconducting properties, including the existence of two phase transitions, the first and second order phase transitions, triple and tricritical points.

Уменьшение магнитных потоков рассеяния в линейных генераторах Вернье с помощью высокотемпературных сверхпроводящих элементов

The article presents the results of studies aimed at improving the power performance indicators of linear electric generators for wave power plants by reducing the flux leakages using high-temperature superconducting (HTS) inserts placed in between the teeth. The generator design involving application of the Vernier principle for magnetic flux modulation with a translator in the form of a hollow cylinder is considered. Generators of this type are used in float wave power plants driven directly by a reciprocating float, which transmits large forces at a low motion speed. The calculations were carried out using the HTS properties modeling procedure based on representing the currents induced in a superconductor in the form of magnetic moments of these currents, which made it possible to simplify the analysis of the electromagnetic field in the generator without significant additional errors. As a result, the characteristics of the electromagnetic force longitudinal components and phase winding flux linkages versus the translator displacement have been obtained. The use of HTS inserts and a distributed winding in the stator made it possible to reduce the electromagnetic leakage losses and increase the interaction force between the stator and translator. However, since the additional outlays for the cooling system and thermal insulation of the HTS elements are commensurable with the generator cost, the obtained results on improving the power performance parameters do not allow an unambiguous statement to be made about the effectiveness of the considered technical solutions.

Theoretical Study of the Effect of Magnetic Field Sweep Rate and Temperature on Shielding Efficiency in a Bulk Tube-Shaped HTS

In this paper, we have studied the shielding properties of a high temperature superconducting (HTS) bulk tube-shaped cylinder in varying magnetic fields. Within this scope, we have simulated the hollow cylinder geometry in axis-symmetric finite element method (FEM) in which the electromagnetic properties of a HTS are described by a nonlinear electric field-current density (E − J) power law including a critical current density depending on magnetic field. In the first stage, we have analyzed temperature dependence of shielding factor (SF), which is described as the ratio of the applied magnetic field to the magnetic field in the center of the hollow cylinder. In the second stage, the effect of magnetic field’s sweep rate (dBapp/dt) on the magnetic shielding was numerically examined. In the final stage, using the certain lines over the superconducting tube, we have worked out the shielding field (Bsz) of the HTS tube by subtracting the z-component of magnetic field (Bz) from applied magnetic field (Bapp). Our numerical investigations indicate that the superconducting tube can provide field and temperature-controlled magnetic shielding.

Comparison of properties of a bulk HTS and a stack of HTS tapes after FC and ZFC

This paper presents the results of the analysis of properties of a high-temperature superconducting (HTS) material in two forms - HTS bulks and a stack made of a number of HTS tape layers. Stack of HTS tape is a new type of application of superconductors, which can be used instead of a convention bulk material. In this work, we study the levitation properties of HTS stack and compare it with the same characteristics of HTS bulks to find the effective way of modelling such type of HTS. Experimental measurements of the force interaction between a permanent magnet and HTS material, as well as a "trapped" magnetic field, are performed for both types of a superconductor. The HTS samples are analysed in the case of Field Cooling (FC) and Zero Field Cooling (ZFC). The aim of the research is to analyse experimental results to compose and justify mathematical models for calculation magnetic system with such types of superconductor.

Effect of the twisting chirality configuration on the electromechanical behavior of multilayer superconducting tapes

Seeking a geometry that can withstand greater transverse loads based on the electromechanical material properties of high-temperature superconducting (HTS) tape is an effective way of improving the transport performance of HTS cables. The cabling method requires the determination of the optimum twist angle of the HTS tape for withstanding transverse loads. This paper investigates the critical current characteristics of HTS tapes under combined deformation. The limit range of the twist angle under the combined deformation is measured and the optimum twist angle of the HTS tape is determined. The results show that the twisting chirality configuration obviously affects the bending strength of the HTS tape. In the elastic range, increasing the pre-twist angle increases the bending strength of the HTS tape, thereby improving the transport performance. In addition, a numerical model is built to further investigate the effect of the twisting chirality configuration on the electromechanical properties of the HTS tape, and the experimental results are explained. The experimental and simulation results generally agree well, and calculations show that there is always a sharp change in stress at the interface of different materials. These findings explain the mechanism of the effect of the twisting chirality configuration on the mechanical behavior and critical current of the HTS tape. They also provide a reference for cabling methodologies for the HTS cable configuration.

Numerical and Experimental Analysis of an Inductive Type Fault Current Limiter Using Short-Circuited 2G Tape

Integrating inductive-type fault current limiters (FCLs) in power grids is envisaged to provide effective protection during severe short-circuit fault occurrences. Numerical simulations are an important class of tools for predicting the performance of these devices under those extreme events. For a proper accuracy of simulations, both electromagnetic and thermal phenomena must be considered. The properties of high-temperature superconducting (HTS) materials, such as electrical resistivity, heat capacity, thermal conductivity, critical current density, and n-index, are strongly dependent on temperature. This is often neglected in transient simulations of devices employing HTS materials, due to unavailability of commercial software easily addressing electromagnetic and thermal interdependence. In this paper, the dynamical behavior of a single-phase inductive-type FCL using a single-turn short-circuited secondary built of HTS second-generation (2G) tape is analyzed by means of a methodology based on the electromagnetic-thermal behavior of the constitutive parts of the FCL. This methodology is fully implemented in MATLAB/Simulink. The transient response during normal and fault operations of line current, primary linked flux, temperature, and current in the 2G tape is simulated and compared with experimental results obtained from a developed prototype. The developed simulation tool provides results in few minutes.

Universal properties of high-temperature superconductors from real-space pairing:t−J−Umodel and its quantitative comparison with experiment

Selected universal experimental properties of high temperature superconducting (HTS) cuprates have been singled out in the last decade. One of the pivotal challenges in this field is the designation of a consistent interpretation framework within which we can describe quantitatively the universal features of those systems. Here we analyze in a detailed manner the principal experimental data and compare them quantitatively with the approach based on a single band of strongly correlated electrons supplemented with strong antiferromagnetic (super)exchange interaction (the so-called $t$-$J$-$U$ model). The model rationale is provided by estimating its macroscopic parameters on the basis of the 3-band approach for the Cu-O plane. We use our original full Gutzwiller-wave-function solution by going beyond the renormalized mean field theory (RMFT) in a systematic manner. Our approach reproduces very well the observed hole doping ($\delta$) dependence of the kinetic-energy gain in the superconducting phase, one of the principal non-Bardeen-Cooper-Schrieffer features of the cuprates. The calculated Fermi velocity in the nodal direction is practically $\delta$-independent and its universal value agrees very well with that determined experimentally. Also, a weak doping dependence of the Fermi wave-vector leads to an almost constant value of the effective mass in a pure superconducting phase which is both observed in the experiment and reproduced within our approach. An assessment of the currently used models is carried out and the results of the canonical RMFT as a zeroth-order solution are provided for comparison to illustrate the necessity of introduced higher order contributions.

Effect of re-pelletization on structural, mechanical and superconducting properties of BSCCO superconductors

We have examined the effect of re-pelletization on structural, mechanical and superconducting properties of high temperature superconducting (HTS) bulk samples using Bi1.85Pb0.35Sr2Ca2Cu3Oy stoichiometry. Conventional solid state reaction method is used for preparation of three different bulk samples. XRD measurement of the samples shows that a high percentage of high-Tc phase is determined. Superconducting critical transition temperature of the samples have been obtained from the curves of ρ-T and χ-T. Vickers micro-hardness are also calculated for all samples. Re-pelletization has a positive effect on structural, mechanical and superconducting properties of bulk samples.

HTS Nested magnet wound with 12 mm GdBCO tape and 4.4 mm YBCO tape

The properties of High Temperature Superconducting (HTS) tapes are progressing, as HTS tapes evolve from 1st generation to 2nd generation. This paper presents design and construction of a 2nd generation HTS magnet consisting of two nested GdBCO and YBCO pancake coils. Two HTS tapes of different widths were used to wind the HTS nested magnet. Considering that a higher magnetic field is applied to the inner magnet than to the outer magnet, 12 mm GdBCO tape was used for winding the inner magnet, which consisted of four single pancake windings. Eight double pancake windings wound with 4.4 mm YBCO tapes were used for the outer magnet. The test results show that the central magnetic field of the HTS nested magnet was 920 mT. The measured critical currents of the inner and outer magnet at 77K were 80.8 A and 32.6 A, respectively.

Numerical simulation of screening current distribution in HTS tape of high field magnet

In recent years, properties of high temperature superconducting (HTS) tapes, especially in-field performance and mechanical strength, have been continuously improved. The HTS tapes have been widely used for high field (>20T) magnet researches and there are several technical challenges including field attenuation of an HTS magnet by screening currents induced within the HTS tapes. Several publications reported that the screening currents, induced by penetration of self magnetic fields into HTS tapes within an HTS magnet, weakened a field constant of the HTS magnet. The result may demonstrate that the screening current changes an overall current density distribution in HTS tapes and, as a consequence, the generated magnetic field. Therefore, it is necessary to investigate the screening current distribution in an HTS tape. This paper reports numerical simulation of the screening current distribution in an HTS tape of high field magnets using 2D finite element method with the E–J characteristic of the HTS tape taken into account. Self magnetic field distribution and its orientation to the HTS tape are also considered to compute critical currents and locally generated electric fields, two key components to figure out the distribution of screening currents.

Trapped Field Analysis of a High Temperature Superconducting Bulk with Artificial Holes

To improve trapped field characteristics of a high temperature superconducting (HTS) bulk, a technique to implement artificial holes has been studied. The artificial holes, filled up with epoxy or metal, may provide better cooling channel and enhance mechanical strength of the HTS bulk. Although many useful researches based on experiments have been reported, a numerical approach is still limited because of several reasons that include: 1) highly non-linear electromagnetic properties of HTS; and 2) difficulty in modeling of randomly scattered “small” artificial holes. In this paper, a 2-D finite element method with iteration is adopted to analyze trapped field characteristics of HTS bulk with artificial holes. The validity of the calculation is verified by comparison between measurement and calculation of a trapped field in a 40 × 40 ㎜ square and 3.1 ㎜ thick HTS bulk having 16 artificial holes with diameter of 0.7 ㎜. The effects of sizes and array patterns of artificial holes on distribution of trapped field within HTS bulk are numerically investigated using suggested method.

Vibrational spectra of silicon cage clusters doped with Ti, Zr, or Hf

We investigate the vibrational modes and infrared spectra of the exceptionally stable isovalent $X@{\text{Si}}_{16}$ ($X=\text{Ti}$, Zr, and Hf) nanoparticles, making use of first-principles density-functional theory. Our results predict the existence of high-intensity modes of low frequency. An estimate of the electron-phonon coupling strength $\ensuremath{\lambda}$ is also provided based on a single-molecule method introduced recently. The large value of $\ensuremath{\lambda}$ combined with predicted stability of bulk materials assembled with these nanoparticles suggest that these materials, when appropriately doped, may exhibit high-temperature superconducting properties.

Superconducting technology for overcurrent limiting in a 25 kA current injectionsystem

Current injection transformer (CIT) systems are within the major group of thestandard type test of high current equipment in the electrical industry, so theirperformance becomes very important. When designing high current systems, thereare many factors to be considered from which their overcurrent protection mustbe ensured. The output of a CIT is wholly dependent on the impedance of theequipment under test (EUT). Therefore current flow beyond the allowable limit canoccur. The present state of the art provides an important guide to developingcurrent limiters not only for the grid application but also in industrial equipment.This paper reports the state of the art in the technology available that could be developedinto an application of superconductivity for high current equipment (CIT) protection withno test disruption. This will result in a greater market choice and lower costs for equipmentprotection solutions, reduced costs and improved system reliability. The paper willalso push the state of the art by using two distinctive circuits, closed-core andopen-core, for overcurrent protection of a 25 kA CIT system, based on a flux-lock-typesuperconducting fault current limiter (SFCL) and magnetic properties of hightemperature superconducting (HTS) elements. An appropriate location of the HTSelement will enhance the rate of limitation with the help of the magnetic fieldgenerated by the CIT output busbars. The calculation of the HTS parameters forovercurrent limiting is also performed to suit the required current levels of the CIT.

Low-energy physical properties of high-Tcsuperconducting Cu oxides: A comparison between the resonating valence bond and experiments

In a recent review by Anderson and coworkers\cite{Vanilla}, it was pointed out that an early resonating valence bond (RVB) theory is able to explain a number of unusual properties of high temperature superconducting (SC) Cu-oxides. Here we extend previous calculations \cite{anderson87,FC Zhang,Randeria} to study more systematically low energy physical properties of the plain vanilla d-wave RVB state, and to compare results with the available experiments. We use a renormalized mean field theory combined with variational Monte Carlo and power Lanczos methods to study the RVB state of an extended $t-J$ model in a square lattice with parameters suitable for the hole doped Cu-oxides. The physical observable quantities we study include the specific heat, the linear residual thermal conductivity, the in-plane magnetic penetration depth, the quasiparticle energy at the antinode $(\pi, 0)$, the superconducting energy gap, the quasiparticle spectra and the Drude weight. The traits of nodes (including $k_{F}$, the Fermi velocity $v_{F}$ and the velocity along Fermi surface $v_{2}$), as well as the SC order parameter are also studied. Comparisons of the theory and the experiments in cuprates show an overall qualitative agreement, especially on their doping dependences.

An optimization method for design of SMES coils using YBCO tape

Recently, the properties of high temperature superconducting (HTS) tapes have been in advance and HTS magnets have been constructed and demonstrated. However, the HTS tapes have thermal different characteristics compared with the low temperature superconducting (LTS) wires. Moreover, Bi2223/Ag tapes and YBCO coated conductors have the different properties about the dependence on the degree of external magnetic field. Therefore it is necessary to consider these characteristics of HTS tapes at magnet design stage. We proposed an optimal design method for superconducting coils using Bi2223/Ag tapes. And the proposed configuration is optimized by using the simulated annealing (SA), which is one of the optimization algorithms, under a lot of constraints such as B-I characteristic, storage energy, and so on. The details of the optimization method and an example of its application to SMES coils (72 MJ) using YBCO coated conductors are shown.

Phase noise of an HTS resonator operated in the nonlinear regime

Nonlinear properties of high-temperature superconducting (HTS) strongly coupled resonators at different input power have been investigated by measurements of the quality factor as a function of input power as well as by generation of the intermodulation distortion (IMD). The double-sided YBCO films on CeO/sub 2/ buffered sapphire demonstrate advanced performance with the microwave surface resistance of /spl sim/0.3 m/spl Omega/ at 8.5 GHz at 77 K and an IMD third-order interception point estimated at P/sub circ//spl ap/70 W. A parallel feedback oscillator was assembled using a transmission type HTS resonator cooled with liquid nitrogen and a room temperature low noise amplifier. Results on the phase noise investigation of the 2.3 GHz oscillator based on HTS resonator operated in the nonlinear regime demonstrated a deviation from the simple model of the phase noise, which predicts an up-conversion of 1/f noise of the amplifier to oscillator phase noise. The latter can be explained by the phase noise introduced additionally due to the nonlinear response of the HTS resonator.

Far-Infrared Transmittance and Reflectance of YBa2Cu3O7-δ Films on Si Substrates

The transmittance and reflectance of superconductive YBa2Cu307-δ (YBCO) thin films deposited on Si substrates have been measured in the far-infrared frequency region from 10 to 100 cm−1 (wavelength from 1000 to 100 μm) at temperatures between 10 and 300 K. The effects of interference, optical resonance, and antireflection on the radiative properties of high-temperature superconducting (HTSC) films are observed and quantitatively analyzed. Furthermore, we have measured the reflectance of the HTSC film-substrate composites for radiation incident on the substrate side (backside reflectance) for the first time. The backside reflectance increases significantly from the normal state to the superconducting state at certain frequencies; this experimentally demonstrates that HTSC films can be used to build far-infrared intensity modulators. The complex refractive index of the YBCO films is determined from the measured transmittance using the Drude model in the normal state and a two-fluid model in the superconducting state. The complex refractive index obtained from this study is useful for various applications of YBCO films, including radiation modulators, detectors, and Fabry-Perot resonators.

Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/ bicrystal grain boundary Josephson junctions

The study of the detailed influence of the order parameter (OP) symmetry on the properties of high temperature superconducting (HTS) Josephson junctions still is a key issue. Whereas the hole doped HTS such as YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO), Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ (BSCCO), or La/sub 1.85/Sr/sub 0.15/CuO/sub 4-/spl delta// (LSCO) are known to have a dominating d-wave component of the OP, there is significant evidence that the electron doped material Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/ (NCCO) has an s-wave symmetry of the OP. Therefore, we have studied the electrical transport properties of [001] tilt NCCO bicrystal grain boundary Josephson junctions (GBJs) with misorientation angles between 7/spl deg/ and 36.8/spl deg/ and compared them to those of the hole doped HTS. For the NCCO-GBJs an exponential decay of the critical current density J/sub c/ with increasing misorientation angle as well as a scaling of the characteristic junction voltage V/sub c//spl prop/J/sub c//sup p/ was found very similar to what is observed for the hole doped HTS. This strongly suggests that the OP symmetry is not the key parameter controlling the characteristic properties of HTS-GBJs. In contrast, they are most likely related to the presence of a disorder induced, insulating grain boundary barrier which is similar for both the d- and s-wave HTS.