High-temperature Superconductors Research Articles

A full-bridge flux pump using two switches: numerical model and experimental prototype

Abstract High-temperature superconducting (HTS) magnets are promising in high field applications. However, due to inevitable joint resistance and flux creep, HTS magnets still face challenges in maintaining field stability in their closed-loop operation. HTS flux pumps can charge closed HTS magnets wirelessly, thus allowing lower cryogenic loading and more flexible arrangements in HTS magnet systems. In this work, a full-bridge flux pump using two AC field-controlled switches is proposed, which can charge HTS magnets during whole cycles. Therefore, the charging speed of the proposed full-bridge flux pump is at least one time larger than half-bridge flux pumps. A numerical model and an experimental prototype are developed to verify the working principle of the proposed full-bridge flux pump. Simulation and experimental tests are carried out to investigate the working characteristics of the proposed flux pump. The proposed flux pump has huge potential in the application scenarios where high charging speed is required.

A tunable dual-narrowband HTS filter using coding superconducting metamaterials aided by grey wolf algorithm

Abstract The design of tunable dual-narrowband high-temperature superconducting (HTS) filter based on coding superconducting metamaterials aided by grey wolf algorithm (GWA) is proposed in this paper. By virtue of the characteristics of right/left-handed bands and scale of deep sub-wavelength, the tunable metamaterials unit loaded with varactor is designed, with coupling types of coding pairs further studied. A tunable sixth-order HTS filter circuit is then constructed, whose layout is effectively optimized by newly developed GWA method. Simulated frequency responses demonstrate that the center frequencies of dual-band respectively locate at 170.1-177.2 MHz (Band I) and 185.2-194.1 MHz (Band II), with 3-dB fractional bandwidth (FBWs) of 0.65%-0.61% and 0.62%-0.57%. The deeply miniaturized circuit size is 0.037×0.046 λ2 g, and the close-to-band rejection level reaches 80-dB. Experimental results of fabricated prototype measured at 70 K validate the feasibility of described design method for high order tunable HTS filter.

Modeling and dynamic performance of distributed force in high-temperature superconducting pinning magnetic levitation

High-temperature superconducting (HTS) pinning magnetic levitation (maglev) systems are highly promising for future applications in rail transportation. Through the interaction between onboard HTS bulks and the permanent magnet guideway (PMG), this system generates levitation and guidance forces, known as the HTS-PMG relationship. Under practical conditions, this interaction manifests itself as a distributed force. However, past models have only considered concentrated forces. This study aims to design experiments to investigate the HTS-PMG relationship and propose a more realistic discretized lateral-vertical coupling HTS-PMG relationship to accurately reflect torques in dynamic simulations. Based on this, a dynamic model is established to analyze the Sperling index and the five-degree-of-freedom dynamic response of the HTS pinning maglev vehicle system under different HTS-PMG relationship models. The results indicate that the proposed discretized lateral-vertical coupling HTS-PMG relationship accurately characterizes the torque generated by the HTS levitator, influencing lateral, roll, pitch, and yaw motions to some extent. Compared with the concentrated force model, the discrete force model exhibits superior dynamic performance, particularly in terms of lateral dynamics and the lateral Sperling index. This study provides valuable insights into the field of HTS maglev, particularly regarding investigating HTS-PMG relationships and their impact on HTS maglev system dynamic performance.

Evolution from a charge-ordered insulator to a high-temperature superconductor in Bi2Sr2(Ca,Dy)Cu2O8+δ

How Cooper pairs form and condense has been the main challenge in the physics of copper-oxide high-temperature superconductors. Great efforts have been made in the ‘underdoped’ region of the phase diagram, through doping a Mott insulator or cooling a strange metal. However, there is still no consensus on how superconductivity emerges when electron-electron correlations dominate and the Fermi surface is missing. To address this issue, here we carry out high-resolution resonant inelastic X-ray scattering and scanning tunneling microscopy studies on prototype cuprates Bi2Sr2Ca0.6Dy0.4Cu2O8+δ near the onset of superconductivity, combining bulk and surface, momentum- and real-space information. We show that an incipient charge order exists in the antiferromagnetic regime down to 0.04 holes per CuO2 unit, entangled with a particle-hole asymmetric pseudogap. The charge order induces an intensity anomaly in the bond-buckling phonon branch, which exhibits an abrupt increase once the system enters the superconducting dome. Our results suggest that the Cooper pairs grow out of a charge-ordered insulating state, and then condense accompanied by an enhanced interplay between charge excitations and electron-phonon coupling.

Relationship between the induced voltage of a rotor bar and the rotation characteristics of a high-temperature superconducting induction motor

Although high-temperature superconducting induction motors have a simple structure, they are distinguished by their high efficiency and high power density. However, an accurate theoretical model that defines the primary electrical characteristics controlling the motor has not been established because of the nonlinear characteristics of high-temperature superconducting squirrel-cage rotor winding. As part of establishing such a model, an experiment was conducted to analyze the relationship between the induced voltage of the rotor bar in a high-temperature superconducting squirrel-cage rotor winding and stator-side quantities (voltage and transport current), as well as its rotation characteristics. A subject was a 1.5 kW class induction motor using Bi–Sr–Ca–Cu–O high-temperature superconducting rotor bars and the experiment was performed at a temperature and a frequency of 77 K and 60 Hz, respectively. The induced voltages of the rotor bars were measured by applying a rotating magnetic field and exhibited a distorted waveform characterized by a third-order harmonic in a magnetic flux flow state. Despite the distorted voltage waveform of the rotor bar, the stator transport current responsible for driving the induction motor remained unaffected and the motor initiated rotation in a slip rotation mode. From the above results, it was experimentally clarified that a stator voltage exceeding the critical current of the rotor bar must be applied when starting the induction motor. It was also shown that the rotor bar can be regarded as a constant resistance for a constant effective value of the stator current when transitioning the motor into a slip rotation state.

Numerical analysis of stacked HTS tapes in rotating magnetic fields using H and T-A formulations

Superconducting windings in rotating electrical machines and multi-phase transformers are subject to rotating magnetic fields. Most existing studies on the electromagnetic characteristics of stacked high-temperature superconducting (HTS) tapes focus on the influence of vertical magnetic field (VMF) and the transport current. The numerical study on characteristics of HTS stacked tapes in rotating magnetic fields (RMFs) has received less research attention. This paper presents two-dimensional models of stacked HTS tapes in RMF based on H and T-A formulations. AC losses obtained by the two formulations agree well in a single tape configuration but significantly differ in a stack configuration. The discrepancy increases as the number of stack layers and the stack interval increase. Under the same magnetic field amplitude, the RMF penetration depth in stacked tapes is higher than those of VMF and parallel magnetic field (PMF), and the parallel component of RMF causes higher AC loss in the end tapes of a stack. While the applied current increases the overall AC loss, it can significantly decrease the AC loss of the end tape. It is found that reducing the stack interval and replacing end tapes with tapes of higher critical current can significantly reduce the overall AC loss of stacked tapes in an RMF. These results are crucial for modeling superconducting machines and offer valuable insights into characterizing superconducting tapes in RMFs using numerical methods.

Numerical study of AC loss and H-formulation for high temperature superconductors

Abstract The high-temperature superconductor (HTS) plays a crucial role in power grids due to its ability to carry high current densities and withstand strong magnetic fields, making it ideal for applications like superconducting magnetic energy storage (SMES). However, integrating SMES systems with the grid introduces challenges, particularly regarding the generation of AC losses during cyclic operations, which can lead to temperature increases in HTS tape. This article presents a method for calculating AC losses and determining the magnetic field formulation at the critical state of HTS using numerical techniques. The study focuses on analyzing the charging and discharging operations of a grid-integrated SMES system based on silicon-controlled rectifiers. Additionally, the critical current of the HTS tape is determined using the four-probe method to characterize its I-V characteristics.

Design and test of a contactless damper for HTS maglev systems via electromagnetic shunt dampers

High-temperature superconducting (HTS) maglev system is promising to become the future high-speed transport due to its numerous advantages. However, the low-damping dynamic characteristics of superconductors make the system vulnerable to external disturbances, which present a significant challenge to its implementation. To enhance the vibration attenuation effect of the HTS maglev system, a non-contact damper that employs electromagnetic shunt damping (EMSD) and negative resistance is incorporated into the HTS maglev system. This study elucidates the principles of EMSD and negative resistance, and establishes the governing equations to describe the behavior of the HTS maglev model equipped with EMSD. Subsequently, the EMSD coupling coefficients are analysed via the finite element method (FEM) under varying conditions. Finally, a dedicated vibration test rig is designed and fabricated to validate the effectiveness of the proposed damper. The results demonstrate that the proposed damper, in combination with negative resistance, is capable of effectively suppressing vibration in HTS maglev systems. The maximum acceleration of the test model can be reduced by 86% compared with the original system without the damper. This work may provide valuable guidance for future practical implementations.

AC loss analysis on an HTS field winding of the generator with T-A formulation

In this study, we proposed a coupling model utilizing finite element software to estimate AC loss on the high-temperature superconducting (HTS) field winding of a 1 MW generator. The model comprises three distinct physical modules: rotating machinery and magnetic (RMM), electrical circuit (CE) and partial differential equation (PDE). These modules collaborate to resolve the generator's magnetic field distribution, rated output parameters and degree of current magnetization on the HTS field winding, employing Maxwell equations and T-A formulation. Given the placement of the HTS field winding on the rotor core, accurately calculating its loss in an electromagnetic field that varies both temporally and spatially presents a considerable challenge. To address this issue, we adjust the coordinate system within the PDE module to vary with the material rather than space. Our analysis reveals that the instantaneous AC loss of an HTS field winding comprises two primary components: the attenuation envelope and the oscillatory variation, resulting from the charging process and external harmonic magnetic fields. Additionally, we comprehensively discuss and analyze the influence of current excitation speed on instantaneous AC loss. Accurately estimating AC loss in HTS field windings is a critical and meaningful aspect of preliminary machine design. This study provides an essential reference for addressing this issue.

Improved prediction of critical currents for multi-pancake coil across variable temperature regions

With the increasing performance of the second-generation high-temperature superconducting (2G-HTS) tapes, the technology of all-REBa2Cu3O7-δ (REBCO, RE: rare earth) superconducting magnets has developed rapidly. However, the 2G-HTS magnet with hybrid cryocoolers constantly adjusts its operating temperature according to the actual demands, which involves the critical current when the magnet crosses variable temperature regions. In this paper, a modified ideal model based on the homogenization model is proposed, which can predict the critical current of 2G-HTS magnets more consistently. The in-field properties of REBCO tapes in variable temperature regions were tested by the physical property measurement system. Furthermore, the improved model was combined with the in-field properties of REBCO tapes to obtain the critical currents of a 2G-HTS multi-pancake (MP) coil at 20 K, 30 K, 65 K, and 77 K. The critical current of a multi-pancake coil at 77 K was experimentally verified. The modified ideal model uses the actual current density, which results are closer to the experimental results with an agreement of 97.3%. This new method proposed in this work is significant in quickly predicting critical currents for 2G-HTS magnets across variable temperature regions.

Superconductors Molecular Effect Model Fundamentals and Review of Isotope Effect with 3D Graphical- Mathematical Interior Optimization

At previous Conference Proceedings, a contribution with computational advances and the review of superconductors (SC) Isotope Effect and Molecular Effect Model (MEM) were presented. That comprised Type I and Type II superconductors materials, both classical and modern ones. 2D/3D Interior Optimization is applied here for further sharper results with numerical dataset in Type II high- temperature superconductors (HTSC). Future challenges in superconducting lines are explained as an author’s proposal, and compared to literature ones. Improved-software results confirm the previous results obtained. A compilation and extension, both in mathematical methods and new results in 3D Graphical and Interior Optimization from the Proceedings presentation is shown and proven. Additionally, a number of previous publications results in this field are included. Applications in Electronics Physics Superconductors modelling are briefed.

High Current Measurement of Commercial REBCO Tapes in Liquid Helium: Experimental Challenges and Solutions

Recent advances in high-temperature superconductors (HTS) have made them extremely attractive for low-temperature, high-magnetic-field-power applications such as in fusion technology, where the advantages over traditional low-temperature superconductors (LTS) allow for the design of fusion reactors operating in different and more convenient regimes. However, the performance enhancement exhibited by novel conductors poses several challenges for the measurement of their superconducting properties. The high critical currents coupled with the relatively low thermal stability of the conductors and their mechanical fragility render this task a challenge, as the angular anisotropies complicate the experimental setup. In this work, we describe the development of our novel high-current measurement facility, focusing on the solutions introduced regarding critical aspects such as the superconducting leads and the sample holder design. We show how simple but effectively designed solutions can be adopted to combat the complexity of the measurement. The results reported in this work guide the development of a measurement system able to withstand high critical currents (I > 1500 A) at high magnetic fields (µ0H > 12 T) by evaluating the angular response of 4 mm wide short samples (L ~ 7.5 cm) in a robust and reproducible manner.

Performance Analysis of Data Acquisition Instruments for High-Temperature Superconducting Devices

Performance Analysis of Data Acquisition Instruments for High-Temperature Superconducting Devices

Electromagnetic and thermal performance study on a canted stack of REBCO tapes

Abstract Due to the critical current limitation of a single REBCO tape, stacking methods are generally employed to increase the current carrying capacity in practical high-temperature superconducting (HTS) applications. However, the overall critical current is strongly dependent on the self-magnetic field, which is influenced by the geometrical arrangement of conductors in the stack. Due to the brittle ceramic property, REBCO tapes are conventionally bent along the thickness side of the tape. However, the difference in bending radii of the outer and inner tape surfaces in the stack may lead to fracture deformation, thereby limiting the stacking number of REBCO tapes. To balance the stacking number with the bending issue, canted stack is proposed as a variant of normal stack for REBCO tapes. As a potential HTS intermediate component, it is imperative to conduct a comprehensive study on electromagnetic and thermal performance of canted stack. The unique geometrical arrangement of canted stack introduces new factors that affect critical current and transport AC loss. This paper concludes the special influencing factors of canted stack, including canted angle, stacking number, tape width, and spatial structure. The metal interleaving method is introduced for spatial distribution changing and thermal stability. Furthermore, orthogonal analysis is performed to elucidate the comprehensive correlation among these multiple factors. This study provides insights into the overall critical current and transport AC loss for different combinations of canted stack and establishes a predicting function for critical current to support the structural design of canted stack. Based on the specific case study, the improvement effect of canted stack is confirmed by both experiments and simulations.

Vibration separation method for permanent magnet guideway irregularity measurement

High-temperature superconducting (HTS) pinning maglev has the potential to achieve high operational speed while having a low maintenance cost, attracting a lot of attention. The HTS pinning maglev system realizes the levitation of the vehicle through the flux pinning characteristics between the high-temperature superconducting bulk and the magnetic field of the permanent magnet guideway (PMG). Thus, the profile of the magnetic field of the PMG can significantly affect the levitation status of the vehicle, which makes the PMG irregularity become one of the main excitation sources of the system. The magnetic induction intensity on the surface of the PMG can be used to characterize the PMG irregularity, but the non-contact dynamic measurement may produce large errors by the vibration of the measurement system during the process. In order to evaluate the PMG irregularity, the vibration component needs to be separated from the overall signal. In this paper, through the synchronous measurement of the Hall sensor and accelerometer, the vibration separation method of the PMG irregularity measurement is simplified to the optimal filter estimation. The particle swarm optimization (PSO) algorithm is used to calculate the parameters of the optimal filter based on the correlation coefficient criterion. The effectiveness of the proposed method is verified by the test. The separated signal is more accurate in both time domain and frequency domain for the characterization of PMG irregularity.

Performance optimization of a neon turboexpander based on the Kriging model and genetic algorithm

The rapid development of high-temperature superconducting (HTS) technology has increased demand for stable and reliable cooling sources, with the neon refrigerator emerging as a favorable solution for HTS applications, among which neon turboexpander is the core component. This paper proposes an optimal design method tailored for the neon turboexpander, which combines a one-dimensional mean-line design, three-dimensional CFD analysis, adaptive Kriging surrogate model, and the genetic algorithm. The meridional contour of the turboexpander impeller is geometrically parameterized, and the three most critical structural parameters are selected through Sobol sensitivity analysis, and then the response surface analysis is carried out to analyze the coupling relationship between the structural parameters. After optimization, the total-to-static efficiency and output power of the neon turboexpander increased by 3.98% and 6.12%, respectively. Notably, the flow separation phenomenon within the optimized impeller is significantly improved, resulting in reduced flow loss. Furthermore, the optimized impeller demonstrates robust performance in a wide range of variable operating conditions. Therefore, the optimization design method has been proven effective, and the optimal turboexpander impeller structure can be obtained quickly and accurately.

Performance enhancements of HTS power cables by minimizing the electric field enhancements for electric transport applications

Abstract Design innovations to manage the electric field enhancements and successful use of cryogenic epoxy EP37 as electrical insulation for high temperature superconducting (HTS) cables for electric aircraft applications are reported. Detailed finite element analysis (FEA) of the electric field distribution shows that the highest electric field is at the interface of the ground and electrical insulation layers. The FEA led to the design, fabrication, and experimental characterization of four model cables with stress cones and a direct bond of the ground and insulation layers. Enhanced partial discharge inception voltage (PDIV) was achieved in the model cables by minimizing the electric field enhancements at the ground layer interface. Using a helium gas mixture with 4 mol% H2, with higher intrinsic dielectric strength than pure helium, further enhanced the PDIV. The results warrant further studies on long HTS cables with EP37 as electrical insulation with a direct bond between the insulation and ground layers.

Unveiling a Novel Insulator-to-Metal Transition in La2NiO4+δ: Challenging High-Temperature Superconductivity Claimed for Single-Layer Lanthanum Nickelates

Abstract La2NiO4 has a similar structure to La2CuO4 and was proposed as a high-temperature superconductor based on magnetic-moment measurements decades ago. Nevertheless, with the exception for electrical resistance drop behavior of about 4 orders of magnitude that is claimed to originate from the superconductivity ever observed in Sr-doped La2NiO4, most electrical data reported to date in La2NiO4 system exhibit a trivial insulating ground state. Here, we definitively identify the similar electrical resistance drop behavior of more than 3 orders of magnitude in La2NiO4+δ . However, our extensive investigations reveal that this phenomenon is a novel insulator-to-metal transition, distinct from superconductivity. Intriguingly, compared to the weak magnetic-field effects, pressure can significantly suppress the transition and transform from the metallic to an insulating ground state, accompanied by an isostructural phase transition. Our work not only elucidates the fundamental properties of the metallic conducting ground state in La2NiO4+δ , but also critically challenges the notion of superconductivity in single-layer lanthanum nickelates.

Techno-Economic Assessment of Coaxial HTS HVAC Transmission Cables with Critical Current Grading between Phases Using the OSCaR Tool

In recent years, the scientific and industrial interest regarding alternative technologies for transmission cables has increased. These conductors should efficiently transmit significant amounts of power between grid nodes, which are expected to be particularly congested due to the projected global increase in electricity production. Superconducting cables are considered a promising solution in this context, offering the potential to transmit large amounts of energy with minimal losses and compact dimensions, thereby potentially benefiting the environment. To evaluate the feasibility of integrating superconducting cables into existing grids, techno-economic approaches should be adopted. Such techniques enable the conceptual design of a specific cable structure, allowing users to explore a wide range of operating parameters to derive optimal designs. This paper reports a comprehensive techno-economic analysis of High Voltage Alternating Current (HVAC) cables realized with High-Temperature Superconducting (HTS) tapes, with the aim to transmit extremely high-power level. The optimal coaxial design is selected using Optimization Tool for Superconducting Cable Research (OSCaR) by implementing a graded approach to the critical current of the HTS tapes used for the different phases. This optimization aims to achieve the most effective balance between the cost of the coated conductors and their electrical properties. The whole set of model equations, the user-defined parameters, and the applied constraints are detailed. The OSCaR tool is then applied to assess the impact on the optimized design of the cable system and the corresponding cost indexes of several crucial parameters, such as the maximum transmitted power, the voltage level, and the line length.

High tolerance of the superconducting current to large grain boundary angles in potassium-doped BaFe2As2

Superconducting magnets based on high-temperature superconductors (HTSs) have become critical components in cutting-edge technologies such as advanced medical applications. In HTSs, weak links of superconductivity are inevitable at high-angle grain boundaries (GBs). Thus, two adjacent grains should be crystallographically aligned within the critical angle (θc), for which the intergrain critical current density (Jc) starts to decrease exponentially. The θc of several iron-based superconductors (IBSs) is larger than that of cuprates. However, the decreases in both θc and intergrain Jc under magnetic fields for IBSs are still substantial, hampering their applications in polycrystalline forms. Here, we report that potassium-doped BaFe2As2 (Ba122:K) exhibits superior GB performance to that of previously reported IBSs. A transport Jc of over 0.1 MA/cm2 across [001]-tilt GBs with misorientation angles up to θGB = 24° was recorded even at 28 K, which is a required level for practical applications. Additionally, even in an applied magnetic field, θc was unaltered, and the decay of the intergrain Jc was small. Our results highlight the exceptional potential of Ba122:K for polycrystalline applications and pave the way for next-generation superconducting magnets.