High-temperature Superconductors Research Articles

FEM-Circuit co-simulation of superconducting synchronous wind generators connected to a DC network using the homogenized J-A formulation of the Maxwell equations

Abstract High-temperature superconductors (HTS) are greatly appealing for the development of high efficient, and high energy density power devices. They are particularly relevant for applications requiring light and compact machines such as wind power generation. In this context, to ensure the proper design of the superconducting machines and their reliable operation in power systems, it is then important to develop models that can accurately include their physics but also can describe properly their interaction with the system. Thus, one approach is the co-simulation. The goal of the present work is to put to use this numerical technique when superconducting components are involved. Here, the case study is a 15 MW hybrid superconducting synchronous generator (HTS rotor and conventional stator) coupled to a direct current (DC) network via a rectifier and its associated filter. The case study related to wind power application allows grasping the technical issues when employing co-simulation dealing with HTS machines. The FEM of the generator is done in COMSOL Multiphysics, which interacts with the circuit simulator Simulink through the built-in Functional Mock-up Unit (FMU). For the present study, a new version of the latest J-A formulation combined with homogenization technique is introduced allowing an even faster computation time compared to the T-A formulation. Distributed variables and global variables such as current density, magnetic flux density, and local losses for the former and voltage, current, electromagnetic torque, and power quality for the latter are estimated and compared for both formulations. The idea is to find the best-suited combination FEM-circuit under criteria of computational speed, accuracy, and numerical stability. It is then shown that all formulations generate an error of less than 5% on the machine parameters; and the J-A formulation with first order elements stands out with a significant 4-fold reduction in computational costs.

Coexistence of superconductivity with partially filled stripes in the Hubbard model

The Hubbard model is an iconic model in quantum many-body physics and has been intensely studied, especially since the discovery of high-temperature cuprate superconductors. Combining the complementary capabilities of two computational methods, we found superconductivity in both the electron- and hole-doped regimes of the two-dimensional Hubbard model with next-nearest-neighbor hopping. In the electron-doped regime, superconductivity was weaker and was accompanied by antiferromagnetic Néel correlations at low doping. The strong superconductivity on the hole-doped side coexisted with stripe order, which persisted into the overdoped region with weaker hole-density modulation. These stripe orders varied in fillings between 0.6 and 0.8. Our results suggest the applicability of the Hubbard model with next-nearest hopping for describing cuprate high–transition temperature ( T c ) superconductivity.

Unconventional superconductivity without doping in infinite-layer nickelates under pressure

High-temperature unconventional superconductivity quite generically emerges from doping a strongly correlated parent compound, often (close to) an antiferromagnetic insulator. The recently developed dynamical vertex approximation is a state-of-the-art technique that has quantitatively predicted the superconducting dome of nickelates. Here, we apply it to study the effect of pressure in the infinite-layer nickelate SrxPr1−xNiO2. We reproduce the increase of the critical temperature (Tc) under pressure found in experiment up to 12 GPa. According to our results, Tc can be further increased with higher pressures. Even without Sr-doping the parent compound, PrNiO2, will become a high-temperature superconductor thanks to a strongly enhanced self-doping of the Ni dx2−y2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${d}_{{x}^{2}-{y}^{2}}$$\\end{document} orbital under pressure. With a maximal Tc of 100 K around 100 GPa, nickelate superconductors can reach that of the best cuprates.

Theoretical characterization and its application of electromagnetic anisotropy in high-temperature superconducting bulks under rotated postures

The electromagnetic anisotropy of high-temperature superconducting (HTS) bulks limits their levitation ability in the applied magnetic fields from the permanent magnet guideway (PMG), thus impeding the enhancement of load-carrying capacity in HTS pinning maglev systems. Developing a suitable matching scheme between bulk orientation and magnetic field direction is a valuable way to relieve this restriction. In this paper, a method for characterizing bulk anisotropy in a rotating coordinate system is proposed to explore the best bulk orientation. The method is based on the concept of equivalent resistivity tensor and its eigenvectors, and includes an extended description of two types of anisotropy: conductivity anisotropy and magnetic field angle dependence. It provides a theoretical foundation for simulating anisotropic bulks under any rotated posture. Experimental investigations on the levitation force distribution of cylindrical bulks with different c-axis orientation were conducted, through which the accuracy of the characterization method and calculated results were validated. Analysis of current distribution reveals that aligning the c-axis parallel to the external magnetic field helps achieve the best match between the bulk and the PMG. Additionally, considering that the two types of anisotropy have opposite effects on levitation force distribution trends, prioritizing conductivity anisotropy when analyzing anisotropic bulk is recommended. This research not only offers a theoretical framework for simulating the anisotropy of rotated HTS bulks but also provides guidance for matching the optimal bulk orientation in applied magnetic fields.

Recent development in high temperature superconductor: Principle, materials, and applications

Superconducting materials, discovered in the early twentieth century, have fascinated scientists with their unique attributes. This review provides a thorough exploration of superconductivity, tailored for newcomers, aiming to be a foundational resource for future research. It traces the evolution of different superconductors, including traditional, cuprate, and non-copper oxide types, detailing their specific characteristics. Central to the review is the examination of theoretical foundations, particularly the BCS theory, and the diverse applications of superconductors in high-performance magnets, energy transmission, and quantum computing. However, the practical deployment of superconductors is limited by challenges, notably their operation at extremely low temperatures, hindering widespread use. Furthermore, economic and technical difficulties in production and maintenance persist. To advance superconductors' potential, research must focus on enhancing critical temperatures and current density and developing cost-effective manufacturing techniques. This will enable novel applications in energy, transportation, and healthcare, driving technological progress.

Improving the screening ability of high-temperature superconductors by combining disk-shaped bulks and closed-loop coated conductors

In this work, we demonstrate experimentally the remarkable DC magnetic screening ability of hybrid superconducting screens. The configurations under investigation combine a 30 mm-diameter disk-shaped superconducting bulk, or another with a 10 mm-diameter hole, with different closed superconducting loops made from coated conductors. The loops are placed coaxially with the bulk. The bulk superconductors and the closed-loop coated conductors are made of GdBa2Cu3O7 and the experiments are performed in liquid nitrogen (77 K). The DC and inhomogeneous field to be screened is produced by a bespoke coil and reaches around 100 mT at the location of the superconducting bulk, which is much less than its full-penetration field. By mapping the magnitude of the flux density using a 3-axis cryogenic Hall probe, we show that such a hybrid superconducting screen allows the maximum shielding factor SF above the bulk to be almost doubled. For the best investigated hybrid configuration, the SF reaches ∼45 at 2.7 mm above the bulk. In addition, the area of the spatial region for which less than half of the applied field remains (SF >2 ) is roughly multiplied by 4 when compared to a situation involving only a disk-shaped bulk. In this work, this region corresponds to a 60 mm-diameter circle. The choice of the loop diameter is found to result from a trade-off between maximum SF and extension of the screened region. Finally, we detail why these hybrid configurations bring such improvements: the key point is that the flux lines generated by the source coil are diverted by the bulk towards a region where the closed-loop coated conductors can oppose the best to them.

A newly developed 10 kA-level HTS conductor: innovative tenon-mortise-based modularized conductor (TMMC) based on China ancient architecture

We proposed a new type of high-temperature superconducting (HTS) conductor concept: modularized conductors (MCs) connected by Chinese traditional tenon-mortise (TM) connection structure, referred as TMMC (tenon-mortise modularized conductor). The conductor consisted of multiple concentric round sub-conductors with slots for stacking rare-earth-barium-copper-oxide (REBCO) tapes. Innovatively, the REBCO stacks in the adjacent sub-conductors were arranged with the fully-misaligned configuration to enhance the critical current’s isotropy with respect to magnetic field and reduce ac loss. For example, the angle between the adjacent stacks in the two adjacent sub-conductors was 45° if each sub-conductor contains 4 REBCO stacks. In order to construct the fully-misaligned configuration, the sub-conductors were designed with two open half-circular formers and connected by TM structure which makes the conductor modularized and simply to assembly and disassembly. Based on the design concept, a prototype conductor containing 160 REBCO tapes distributed in the four concentric sub-conductors was fabricated. The conductor’s measured critical current was 13.69 kA at 77 K and self-field, which was consistent to the simulation result. In order to further improve the TMMC’s engineering critical current density (J ce) and bending performance, we proposed two enhancement approaches: reducing the former’s thickness and re-arrange stacks in the outer sub-conductors. With the enhancements, both TMMC’s radius and J ce were comparable to the existing slotted-core conductor. The study shows the TMMC’s advantages of non-twisted structures, easy assembly, high-current carrying and low ac losses, which made it promising for constructing large-scale scientific devices.

Superior Superconducting Properties Realized in Quaternary La-Y-Ce Hydrides at Moderate Pressures.

The recent revolution in the superconductivity field stems from hydride superconductors. Multicomponent hydrides provide a crucial platform for tracking high-temperature superconductors. Besides high superconducting transition temperature (Tc), achieving both giant upper critical magnetic field [μ0Hc2(0)] and high critical current density [Jc(0)] is also key to the latent potential of the application for hydride superconductors. In this work, we have successfully synthesized quaternary La-Y-Ce hydrides with excellent properties under moderate pressure by using the concept of "entropy engineering." The obtained temperature dependence of the resistance provides evidence for the superconductivity of Fm3m-(La,Y,Ce)H10, with the maximum Tc ∼ 190 K (at 112 GPa). Notably, Fm3m-(La,Y,Ce)H10 boasts exceptional properties: μ0Hc2(0) reaching 292 T and Jc(0) surpassing 4.61 × 107 A/cm2. Compared with the binary LaH10/YH10, we find that the Fm3m structure in (La,Y,Ce)H10 can be stable at relatively low pressures (112 GPa). These results indicate that multicomponent hydrides can significantly enhance the superconducting properties and regulate stabilizing pressure through the application of "entropy engineering." This work stimulates the experimental exploration of multihydride superconductors and also provides a reference for the search of room-temperature superconductors in more diversified hydride materials in the future.

Diffusion models for conditional generation of hypothetical new families of superconductors

Effective computational search holds great potential for aiding the discovery of high-temperature superconductors (HTSs), especially given the lack of systematic methods for their discovery. Recent progress has been made in this area with machine learning, especially with deep generative models, which have been able to outperform traditional manual searches at predicting new superconductors within existing superconductor families but have yet to be able to generate completely new families of superconductors. We address this limitation by implementing conditioning—a method to control the generation process—for our generative model and develop SuperDiff, a denoising diffusion probabilistic model with iterative latent variable refinement conditioning for HTS discovery—the first deep generative model for superconductor discovery with conditioning on reference compounds. With SuperDiff, by being able to control the generation process, we were able to computationally generate completely new families of hypothetical superconductors for the very first time. Given that SuperDiff also has relatively fast training and inference times, it has the potential to be a very powerful tool for accelerating the discovery of new superconductors and enhancing our understanding of them.

Quantile regression-enriched event modeling framework for dropout analysis in high-temperature superconductor manufacturing

Quantile regression-enriched event modeling framework for dropout analysis in high-temperature superconductor manufacturing

Superconducting Two-Dimensional FeSe Grown on the Fe-Enriched Interface.

Two-dimensional (2D) tetragonal FeSe has sparked extensive research interest owing to its tunable superconductivity, providing valuable insights into the design of high-temperature superconductors. Currently, the intricate Fe-Se phase diagram poses a challenge to the controlled synthesis of superconducting 2D FeSe in a pure tetragonal phase. Here, we exploit the ion-exchange property of fluorophlogopite mica to devise a straightforward approach for the phase-controlled synthesis of tetragonal FeSe on an Fe-enriched mica surface within a molten salt environment. This method successfully produces highly crystalline FeSe in a pure tetragonal phase with adjustable thickness. We investigated the surface composition of the postgrowth mica substrate using various microscopic and spectroscopic characterizations to highlight the importance of the Fe-enriched growth interface in the phase-selective synthesis of 2D tetragonal FeSe. The obtained 2D FeSe exhibited 2D superconductivity, comparable to that of FeSe mechanically exfoliated from bulk crystals, confirming the high quality of our samples. Beyond tetragonal FeSe, 2D antiferromagnetic FeTe and superconducting FeSxSeyTe1-x-y have been phase-selectively synthesized via this approach. Our study elucidates the significance of the growth interface on the phase-selective synthesis of 2D materials and presents potential opportunities for the phase-controlled synthesis of 2D multiphase materials via the rational design of the growth interface.

Design and Thermal Analysis of a 250 MVA HTS Transformer for Substation of Offshore Wind Farms

In Offshore Substations (OSs), using High Temperature Superconducting (HTS) transformers instead of conventional power transformers to reduce operational and construction limitations such as weight, capacity, marine pollution, and future planning can be considered as desirable. HTS transformers can reduce operating system costs in wind power plant development programs. However, OSs have specific operating conditions in fault mode that should be considered in the design HTS transformers.In this paper, a 250 MVA 33/220 KV HTS transformer is designed, and electromagnetic analysis is done in normal conditions to calculate AC loss and thence to design the cooling system. The second step, thermo-flow analysis is done by Finite Element Method (FEM) to calculate the temperature distribution of the windings. Increasing turbulence of inlet flow and creating a porous coating on the tapes are used in this transformer to increase the heat-transfer rate. lastly, the specifications of the HTS transformer are compared with the conventional transformer to give useful information to OS designers to investigate using novel construction ideas such as floating OS by HTS transformer.

Mechanical behavior of multi-layer CORC cable in high external field with 3D numerical model

The degradation of critical current due to mechanical deformation in a high field has a profound impact on the performance of high-temperature superconducting (HTS) structures. The multi-layer conductor on round core (CORC) cable is a widely-applied HTS structure in engineering. Due to the complexity of the multi-layer CORC cable, the contact between the tapes should be considered when simulating the mechanical behavior in high field. In this paper, 3D electromagnetic and mechanical models were developed to investigate the mechanical behavior of the multi-layer CORC cable. Under the same electromagnetic force, the comparisons of mechanical models of a 5-layer CORC cable with different contact methods are presented. Subsequently, the effects of the loading path of the external magnetic field and transport current, the bending geometry of the CORC cable, the winding direction of the HTS tape in the CORC cable, and the shielding current on the mechanical behavior are discussed, respectively. The numerical results are useful for the design and operation of CORC cable in high field.

Multilayer neural network models for critical temperature of cuprate superconductors

A multi-layer neural network is used to extract the value of a superconductor’s Tc of cuprate from two models. The first model extracts Tc from the structure’s chemical composition whereas the second model extracts Tc from the structure’s chemical composition and the lattice parameters. The back-propagation algorithm is used to find the empirical equation of Tc. It can calculate error signals and redistribute backward propagation signals. This paper studies four systems of cuprate superconductors: Y-Ba-Cu-O, Bi-Sr-Ca-Cu-O, Tl-Ba-Ca-Cu-O, and Hg-Ba-Ca-Cu-O. In the first model, the Tc of four high-temperature oxide superconductors are calculated as a function of eight parameters and one output, which is Tc. Although the same output is produced in the second model, it is produced as a function of eleven parameters. The eight parameters are superconductor type number (Bi2212, Bi2223, Hg1201, Hg1212, Hg1223, Y123, Y124, Y247, Tl1223, Tl2212, Tl2223), first component composition, second component composition, third component composition, fourth component composition, atomic number of doping type, doping composition, and oxygen composition of the first model. The previous parameters with the three lattice parameters a, b and c are used in the second model. The trained deep learning models have shown a high degree of performance in matching the trained distributions. After analysing the results, we deduce electronegativity plays an important role in increasing Tc of cuprate superconductors. Using the obtained Tc prediction model, the scope is expanded to include the eleven unexplored multi-element materials. Candidates for superconductors with a higher Tc that can be synthesised are proposed. By comparison with other models of machine learning, the suggested models in this paper give the highest Tc for predicting new cuprate superconductors.

Effect of Ca-Cu-O Particle Size on the Phase Evolution Process of Bi-2223 High-Temperature Superconductors

Effect of Ca-Cu-O Particle Size on the Phase Evolution Process of Bi-2223 High-Temperature Superconductors

The Interaction Between a High-Temperature Superconducting Coil and In-Series Permanent Magnets

The Interaction Between a High-Temperature Superconducting Coil and In-Series Permanent Magnets

Influence of D-Q Current on No-Insulated High-Temperature Superconducting Magnets for Wound-Rotor Synchronous Motors

Influence of D-Q Current on No-Insulated High-Temperature Superconducting Magnets for Wound-Rotor Synchronous Motors

Development of a superconducting undulator cryostat based on the thermosiphon effect

As a specific device for light production, undulators have been researched and developed since the third generation of synchrotron photon sources. Nowadays, superconducting undulators become a research hotspot. However, the cryostat, which is used to create a liquid helium temperature environment, often causes the failure of the superconducting undulator. In this paper, a cryostat for a superconducting undulator is designed and investigated. First, a new refrigeration distribution is proposed that can provide more excess cooling capacity at 4.2 K temperature. For the cooling of the superconducting magnet, a liquid helium circulation loop based on the thermosiphon effect is designed, which has no pump or any other moving parts. Next, based on high-temperature superconducting technology, six binary current leads are used to decrease the heat load. The beam chamber is cooled below 20 K to reduce possible effect on the magnet. In addition, for the tubes that connect the 4.2 K helium tank to the room temperature component, the thermoacoustic oscillation is studied. In the experiment, the superconducting magnet could be cooled and maintained at 4.2 K depending on the thermosiphon loop. No helium was discharged when the magnet went through a quench which generated large heat in a short time. There was no liquid helium consumption and the excess cooling capacity reached 2.2 W. The maximum magnet current is as high as 470 A. This study can provide a valuable reference for the development of superconducting undulator cryostats.

3D modeling and measurement of HTS tape stacks in linear superconducting magnetic bearings

Superconducting magnetic bearings (SMBs) are among the possible new technologies to be incorporated in maglev vehicles. Stacks of high-temperature superconductor (HTS) tapes can be used as an alternative to bulks, because stacks offer better mechanical properties, a better thermal conductivity and a simpler production process. Numerical modeling has been employed as a cost-effective, fast and reliable tool for improving the performance of SMBs. Several scenarios can be simulated with fast and relatively simple 2D models; however, in some cases using 3D models is inevitable. In this study, we use a full 3D model to solve the problem of magnetization of the tape stacks and obtaining the hysteresis force loop between a permanent magnet and the tape stacks. For this purpose, we employ an energy minimization-based method called minimum electromagnetic entropy production in 3D, combined with a homogenization technique and the Jc(B,θ) dependence of the HTS tape as input. The modeling results agree very well with the experiment both in the zero-field cooled and field-cooled conditions. The presented approach offers significant computational advantages, delivering faster and more efficient results compared to previously proposed 3D methods.

23 Tesla high temperature superconducting pocket magnet

Abstract We present a compact 23 T no-insulation (NI) magnet that was wound with 60 m of 10 mm wide high temperature superconducting (HTS) tape. The magnet consists of only one pocket-sized double pancake (DP) coil with an inner diameter of ~6 mm, a height of 20 mm, and an outer diameter of 41.6 mm. Another NI coil of similar size but with a larger inner diameter of 8 mm reached a slightly lower magnetic field of 21 T. We also present a smaller coil which was wound with only 20 m of HTS tape and still achieved a magnetic field of 16 T. During the experiments in liquid helium, each coil was charged to a current between 700 A and 800 A, corresponding to a high current density of 1500-1900 A/mm2. The small bore size and high current density contributed to the high fields generated by these coils. We present the fabrication details, helium tests and repeatability analysis of these “pocket” magnets.