Electrodynamic suspension (EDS) technology employs superconducting magnets for passive levitation and propulsion in high-speed transportation, offering enhanced energy efficiency. A critical challenge, however, lies in the eddy current losses induced in the on-board magnet's cryogenic components by time-varying magnetic fields from ground-based propulsion coils during nonsynchronous operations like start-up or braking, which generate heat that compromises thermal stability. This article establishes a combined numerical and experimental framework to address this issue. First, a 3-D numerical model based on the A-formulation is developed to predict eddy current loss distribution within a novel, lightweight high-temperature superconducting (HTS) magnet system featuring an all-aluminum-alloy cryostat. Subsequently, a static equivalent measurement system is implemented, utilizing a calorimetric method to accurately measure losses under simulated dynamic conditions. The experimental results show good agreement with the simulations, validating the model's predictive accuracy. Key findings include the identification of a distinct loss peak near 100 Hz, attributed to the influence of penetration depth and skin effects in the aluminum structures, clarifying the frequency-dependent loss mechanism. Furthermore, a comparative analysis with a previous magnet generation demonstrates that the all-aluminum-alloy design achieves a significant weight reduction of over 30% and effectively suppresses eddy currents near the critical current leads, despite a moderate temperature rise in the coil cases. These insights provide valuable guidance for the design and optimization of thermally stable and lightweight HTS magnets, contributing to the reliability of next-generation EDS systems.

No-insulation (NI) high-temperature superconducting (HTS) magnets are promising for high-field applications due to their inherent self-protection capability. Nevertheless, the reliable detection of localized quench (thermal runaway) remains a crucial challenge for operational safety. This paper presents a non-invasive quench detection method utilizing a distributed Hall-sensor array, which monitors magnetic field variations resulting from current redistribution during a quench. The method is fundamentally grounded in the whole-turn current-sharing mechanism, elucidated by a circuit-based theoretical analysis. This mechanism explains that a local thermal event initially induces current to redistribute across adjacent turns, generating a spatially extended and azimuthally uniform magnetic field perturbation. Consequently, a limited number of external sensors can effectively capture the quench signal. Experimental studies on an NI HTS magnet under local thermal disturbances confirm the method's reliability. The method’s principal advantage is its non-intrusive nature, which preserves the magnet’s intrinsic integrity by avoiding the disturbances to turn‑to‑turn contact inherent to invasive sensors. Furthermore, simulation results delineate the operational stability limits: NI HTS magnets exhibit robust stability under high-temperature, low-current conditions due to insufficient loss generation, whereas under low-temperature, high-current operation, a high turn-to-turn contact resistivity (on the order of hundreds of µΩ·cm² or higher) significantly increases the risk of an irreversible quench. To ensure safety against local critical current degradation, a design current margin of 30% is recommended. The proposed detection strategy and comprehensive analysis provide critical insights for the design and protection of NI HTS magnets, facilitating their practical application.

This study focuses on the development of a high-efficiency computational model for predicting the magnetic field of high-temperature superconducting (HTS) magnets, which is crucial for the design and optimization of HTS-based devices. A fast-computational model for magnetic field was proposed, leveraging the feature extraction capabilities of the deep residual neural network. To validate the effectiveness and reliability of the proposed model, a prototyped HTS magnet system was employed for experimental verification. The comparison between the calculation results and the experimental data demonstrated a high degree of consistency, confirming the practical applicability of the model. Subsequently, an enhanced linear adaptive genetic algorithm was introduced for the optimization design of a 3 T magnetic resonance imaging magnet utilizing rare-Earth barium copper oxide superconducting tapes. The optimized magnet is composed of 60 double-pancake coils, operating at a cryogenic temperature of 30 K and featuring a coil inner diameter of 600 mm. An active shielding technique was adopted, which involves the strategic arrangement of additional coils to counteract the stray magnetic fields. Through this approach, the fringing field was effectively suppressed. In terms of field homogeneity, the magnet achieved 74 parts per million within a 250 mm diameter spherical volume.

No-insulation (NI) high-temperature superconducting (HTS) coils are widely used in many applications because of their higher current density, excellent mechanical properties, and self-protection capability. However, because their current transmission path is not unique, the modeling of NI coils becomes more complex compared to the insulated one. In this paper, we have established a field-circuit coupling model based on the J-A formulation and validated its accuracy during both transient charging/discharging and external magnetic field exposures. The results indicate that the proposed model is capable of effectively characterizing the overall behavior and local characteristics of the NI HTS coils. Specifically, the local properties are validated against AC loss measurements under external alternating magnetic fields. Based on the developed model, a small-scale pancake NI coil was fabricated to investigate the factors governing the AC losses in such small pancake coils under both radial and axial background magnetic fields with DC transport current. Results reveal that axial fields induce significantly higher AC losses in NI coils compared to radial fields. Notably, under radial magnetic fields, the loss patterns of NI coils exhibit negligible differences from those of insulated coils. These insights contribute to magnetic field configuration optimization and loss management in NI coil applications.

Abstract No-insulation (NI) high-temperature superconducting (HTS) magnets have achieved significant progress owing to their superior thermal stability and self-protection capability. However, under multi-source time-varying disturbances and local material defects, the accumulation of internal heat load within NI HTS magnets may alter its electromagnetic properties and inter-turn contact conditions, thereby potentially resulting in a quench event. Therefore, quench detection and prediction technologies are essential for ensuring the operational safety of the NI HTS magnets. To address this issue, a quench experimental platform is first established to monitor the operating states of the magnet through magnetic field signals. Afterwards, combined with the corresponding simulation models incorporating inter-turn electromagnetic-thermal coupling, a multi-channel magnetic field time-series dataset is constructed based on neural network algorithms to characterize the quench behavior of a NI HTS magnet. Finally, the quench prediction performances of three neural network models are comparatively analyzed. The results demonstrate that the convolutional neural network-Gated Recurrent Unit model exhibits superior performance, achieving a coefficient of determination ( R 2 ) of approximately 0.9991 ± 0.0004 between the predicted and true values in the single-step prediction case. For long-sequence quench prediction cases, the model maintains robust performance ( R 2 = 0.92 ± 0.06) even for 100-step predictions, thereby validating the generalization capability of the neural network. Although the stability of prediction accuracy for experimental data in the long-sequence forecasting still requires further improvement, both quantitative and trend prediction results provide valuable early detection of quench behavior in the NI HTS magnets.

Cryogenic pulsating heat pipes (PHPs) offer a simple, lightweight, and cost-effective solution for cooling hightemperature superconducting (HTS) magnets, and have the potential to replace high-conductivity metals such as oxygen-free high-conductivity copper. Despite their promise, the influence of geometric constraints, particularly bending angle, on cryogenic PHP performance has not been systematically studied. This work presents the first comprehensive experimental investigation of liquid-neon PHPs with different bending angles (30 degrees, 45 degrees, and 60 degrees) and filling ratios (40-80 %). Results show that a 30 degrees bending angle combined with a 65-70 % filling ratio yields the best thermal performance, supporting stable oscillations and the highest effective heat transport capability. Compared with larger bending angles, this configuration enhances thermal performance and extends the operating heat load range. These findings not only establish a clear design guideline for cryogenic neon PHPs but also provide practical insights for integrating PHPs into next-generation HTS magnet cooling systems.

This paper presents an analytical method for modelling the acoustic field radiation from a semi-infinite elliptic duct in the presence of uniform subsonic flow. In contemporary aircraft design, elliptic ducts play crucial roles as inlets for advanced blended wing body configurations owing to their capacity to maximise the pre-compression effect of the fuselage and enhance the stealth performance of aircraft. The method uses Mathieu functions to describe the incident and scattered sound in the elliptic cylindrical coordinates. An analytical Wiener-Hopf technique is developed in this work to derive near- and far-field solutions. Numerical simulations based on a finite element method are conducted to validate the accuracy of the analytical method, revealing a strong correspondence with analytical predictions. A parametric study is conducted to explore the influence of the elliptic cross-section shape on noise directivity. Moreover, we investigate reflections within the duct via an extended derivation of the analytical model. The proposed method can be used to examine the acoustic characteristics of elliptic ducts with inflow mean flows, which holds relevance for noise control and optimisation of turbofan engine inlets and blended wing body applications.

No-insulation (NI) high-temperature superconductor (HTS) coils introduce turn-to-turn electrical paths, enhancing their thermal stability and self-protection capacity against quenching. However, the extra turn-to-turn electrical paths complicate both the geometrical and physical modeling of HTS coils. This article presents a field-circuit coupled model where the HTS component is treated as a global voltage parameter that contains resistive and inductive voltage in the circuit model. The superconducting branch current in the circuit model serves as external current input to the NI HTS coil. The finite element method model is based on an anisotropic resistivity model governed by the J-A formulation, considering the current-sharing effect of the metal layers in the coated conductor under overcritical current state. To validate the proposed model comprehensively, two key characteristics are illustrated: first, comparing experimental measurement data of sudden discharging, charging, and overcritical current state; second, comparing computing efficiency with the prevailing H-formulation model. The results show that the calculated results are in good agreement with the experiment, the validity, and applicability of the proposed model are well verified. In comparison to the H-formulation model, the computational efficiency of the proposed model is improved by more than 82% without sacrificing the computational accuracy. In addition, with the proposed model, it has been found that the current-sharing effect of the metal layers is negligible in the overcritical current state. To verify the wider applicability of the proposed model, we simulated charging the closed-loop NI HTS coils with a flux pump. The proposed model can better characterize the voltage source excitation properties and analyze the frequency saturation of the charging time constant. Based on this, we have further investigated the superconducting resistive losses as well as the turn-to-turn losses at different traveling wave frequencies.

High-temperature superconducting (HTS) coils are generally operated in a closed-loop persistent current mode, which is crucial for ensuring long-term stability and minimizing heat generation in various applications. However, factors such as joint resistance, flux creep, and losses due to external fields can lead to accelerated decay of the coil's current, making it challenging to achieve an effective persistent current mode. To gain insight into the current decay characteristics of HTS coils, we built a finite element method based model coupled with a lumped parameter electric circuit model. The model is initially verified against the experiment of an inductive magnetized HTS coil subject to a magnetic field perpendicular to the tape surface. The results indicate that the proposed model is highly effective in predicting the current decay behavior of this magnetized HTS coil and is able to provide high accuracy. With the help of this model, we have experimentally and numerically studied the behavior of a current-carrying closed-loop HTS coil subject to external alternating fields. The HTS coil is charged by a DC power supply and then shorted using a thermally-controlled persistent current switch. The current decay behavior of the HTS coil is examined under various scenarios. The simulation results show excellent agreement with experimental data, further validating the effectiveness and versatility of the modeling strategy. The influence of both local and global screening currents on the current decay performance of the closed-loop HTS coils has been investigated. For every case examined, rapid demagnetization occurred in the initial cycle of the applied alternating field. Furthermore, the current decay rate demonstrated a slight dependence on the frequency of the applied fields. Additionally, the resulting resistance has been thoroughly characterized. These insights contribute to the knowledge of the behavior and performance of closed-loop HTS coils, facilitating their practical application.

High-temperature superconducting (HTS) magnets are promising candidates for transportation and power systems, such as the electrodynamic suspension (EDS) train, ultra-high field magnet and magnetic resonance imaging, because of their large current-carrying capacity and low power loss. The critical current depending on magnetic flux density is an essential factor in assessing the application performance of HTS magnets. As usual, the existing HTS magnet is wound with rectangular cross-section, which results in magnetic field concentration inside winding. In this paper, we propose a novel HTS magnet structure with stepped cross-section to alleviate the magnetic field concentration, and resultantly improve the critical current. From this point, this paper aims to design and optimize a stepped HTS magnet with the critical current maximized. Firstly, the structure design of the stepped HTS magnet is performed with a consideration of the application scenario of EDS train. Then, the critical current of the HTS magnet is estimated with a homogenized self-consistent model. Afterwards, an HTS magnet with stepped cross-section is optimized, fabricated and finally tested. The critical current was experimentally measured to verify the simulation results, followed by the electromagnetic investigations of the stepped HTS magnet in the EDS train.

A double-layer metal-insulation method using brass sheets as the double-layer insulators is proposed in this paper. It can enhance the contact resistivity while preserving greater thermal conductivity merit. The underlying mechanism of the contact resistivity enhancement is to increase the number of contact surfaces and to degrade the contact quality between the insulators. Then, we wound a single-layer brass-insulation coil and a double-layer brass-insulation coil to compare their contact resistivities, and confirmed the effectiveness of the double-layer metal-insulation method. Furthermore, since the capacity to withstand the overcurrent is weakened with the increasing contact resistance of the metal-insulation coil, we further investigated the influence of the contact surface resistivity distribution on the coil performance under different scenarios to optimize the double-layer metal-insulation coil for receiving superior thermal stability. The simulation results indicate that dominant second contact surface resistivity and minimal first and third contact resistivity is the optimal design for the double-layer metal-insulation coil to receive the best thermal stability, irrespective of the cooling environment, contact resistivity magnitude, operating current and coil dimension. In addition, with regard to the thermal performance differences caused by the contact surface resistivity distribution, we found that the increment of contact surface resistivity and the overcurrent enlarged the distinctions at different levels.

A small ducted fan with a rotor-stator assembly is being tested in an anechoic chamber at Peking University. To attenuate fan noise, turbulence grids have been inserted before the rotor to eliminate large-scale ingested flow structures and, therefore, to minimize the flow interactions between the rotors and stators. Several different grids with various geometry and solidity configurations have been considered in the tests. To demonstrate the proposed noise control method, both near-field in-duct on-surface microphones and far-field microphones are used to measure acoustic performance. In addition, a microphone array is deployed to acoustic images at several working conditions. The corresponding thrust performance, with and without the grids in between the rotors and stators, is being measured simultaneously. The possible fluid mechanics is presumably caused by the reduced strength of ingested turbulence structures. More results help to reveal this physical understanding will be given in the final manuscript. Through this work, we hope to investigate a new strategy that could possibly reduce UAV fan noise at several representative working conditions.

The superconducting electrodynamic suspension (EDS) train has been expected to be a promising candidate for the future ultrahigh-speed transportation due to its excellent levitation and guidance stabilities, high lift-to-drag ratio, and being free of active control. As a core component of the EDS train, the onboard superconducting magnet (SCM) is usually required to generate a strong magnetic field, however, which may threaten the safety of passengers. Therefore, it is indispensable to design a magnetic shielding for onboard SCM, aiming at minimizing the magnetic field in the coach of the vehicle. In this article, a three-dimensional finite-element method model for solving the electromagnetic problems of the magnetic shielding system is established and validated by experimental results. Prior to global optimization, the effects of the thickness, multilayer structure, and partition of the shielding plate on the magnetic shielding are discussed primarily. It was found that the thickness has a great impact on the shielding effect, whereas the influence of the multilayer structure is weak. Moreover, the weight of the magnetic shielding plate can be effectively reduced by partitioning it into several blocks with different thicknesses. Based on the above-mentioned studies, the magnetic shielding plate is finally optimized in consideration of the thickness, multilayer structure, and partition. Consequently, the weight of the magnetic shielding plate can be reduced by 20% compared with the original one.

High-temperature superconducting magnets wound by REBCO (rare-earth-barium-copper-oxide) coated conductors are promising candidates for electrodynamic suspension system due to their high current-carrying capability, excellent mechanical tolerance and low cooling cost. Solid nitrogen as coolant to protect HTS magnets can significantly promote their dynamic performance and reduce the use of auxiliary equipment, which reduce the system dimension and weight. In this study, we propose a mechanical-thermal coupling model of solid nitrogen cryostat for electrodynamic suspension system. This model is capable of calculating the temperature distribution during cooling process and the transient behavior for the rewarming process of the solid nitrogen cryostat. The cooling capacity map for the two-stage RDK-415D cryocooler was extended for accuracy. The steady state temperature distribution of cooling process and the thermal evolution of three different rewarming processes, including cryocooler reserved, 5 W losses applied and cryocooler detached, were calculated and verified experimentally, followed by the investigation of the structural stresses and displacement of the solid nitrogen cryostat due to thermal displacement among different components. The developed model can serve as a reference and guide for the design and optimization of solid nitrogen cryostat for electrodynamic suspension system.

In this article, we propose a novel analytical-experiment coupling method to characterize the electromagnetic forces of superconducting electrodynamic suspension system. The basic idea of this method is that, the induced currents of the ground null-flux coils (NFCs) are predicted by analytical calculation, but the electromagnetic forces on the onboard superconducting magnets are directly measured. To ensure the calculation accuracy of induced current, a Neumann's formula-based analytical model was derived and its accuracy was confirmed by comparing with the finite-element model and the existing analytical model, which is based on the harmonic approximation. The prominent merit of this method is that it is free of high speed rotating motion and thus, has no limitations of testing speed. We further made a proof-of-principle experimental setup, which consists of a coated-superconductor magnet and a few NFCs, to check the effectiveness of the proposed method. By this setup, the dependence of electromagnetic forces, i.e., levitation force, guidance force, and drag force, were measured as a function of displacement and speed. It was found that, results obtained by the proposed method are in agreement with 3-D finite-element simulation, which to some extent validatesthe proposed method.

The introduction of high temperature superconducting (HTS) magnet, which is capable of working at liquid nitrogen temperature, and the use of null-flux coil, make the liquid-helium-free electrodynamic suspension (EDS) train available. In essence, the electromagnetic force of a superconducting EDS train is generated by electromagnetic interaction between the onboard superconducting magnets and the ground null-flux coils. In order to obtain an efficient HTS EDS train, the design optimization of the HTS magnets and null-flux coils is indispensable. This study is devoted to this aspect. We first establish an improved load-line method for efficiently estimating the critical current of HTS magnets and an improved semianalytical model to accurately calculate the induced currents and electromagnetic forces in the EDS train. Based on above two improvements, the onboard HTS magnets and corresponding null-flux coils are then designed and optimized to enhance the overall performances of the HTS EDS train. At final, according to the optimized results, the HTS magnets and null-flux coils were manufactured and measured, followed by the performance analyses of the obtained HTS EDS train. The results have shown that the electromagnetic performances of the designed HTS EDS train are excellent, demonstrating the effectiveness of the optimization methodology.

以YBCO(YBa2Cu3O7-δ)为代表的二代高温超导带材因具有高临界转变温度、高临界磁场和强载流能力,受到了国际学界高度关注,在各个领域具有广泛的应用前景.二代高温超导带材在绕制、冷却和运行过程中会受到不同来源的外力作用,且超导带材的韧性、延展性较差,因此其机械性能是影响安全性与设备运行可靠性的关键.本文基于二代超导带材各向异性的特点,对超导带材轴向、横向、弯曲三个方向的静态机械性能及疲劳性能进行了介绍.同时,也对超导带材各方向机械性能的测试方法、影响因素及机理进行了总结.

High-temperature superconducting (HTS) magnets have been investigated widely for their higher upper critical magnetic field, larger engineering critical current density and simpler cryogenic system compared with low-temperature superconducting magnets. However, in order to keep the permanent-current mode of the HTS magnets, the external power supply is usually employed to charge the magnet via copper current leads, which is a considerable heat source to the cooling system. Thus, in order to avoid the heat disturbance brought by the current leads, a new ‘through-wall’ dynamo-type HTS flux pump using a pair of magnetic couplers is proposed, realizing the truly wireless power transfer, and exploring its possible application for the conduction cooled system. Based on the proposed structure, the heat conduction, which was calculated to be about 7.75 W, and heat convection could be minimized. In addition, to further improve the charging performance of the dynamo-type flux pump, a ferromagnetic (FM) slice was added at different positions of the system. The effect of the FM slice on charging performance is studied numerically and experimentally. According to the results of simulations and experiments, adding an FM slice under the HTS stator improves the saturated current and the charging speed of the dynamo-type flux pump by 20%–30%.

Superconducting linear synchronous motor (LSM) with super-conducting magnets as its secondary is a promising candidate for driving high-speed transportations. The superconducting secondary operates at an ultra-low temperature environment generally supplied by a complex cryogenic system that contains numerous metal components, in which the eddy current losses are produced due to the magnetic fields from the primary. The ensuing temperature rise will inevitably lead to a reduction in the current-carrying capacity of superconducting secondary and threaten the operation safety of LSM. It is crucial to clarify the eddy current losses. To this end, we established a three-dimensional numerical model based on the A-formulation of Maxwells equations. In this model, a kind of virtual primary was introduced to efficiently simulate the movement of the sec-ondary instead of through a moving mesh technique since that is no longer suitable for this calculation. Afterwards, a testing set-up of the superconducting LSM was constructed and the eddy current losses in the superconducting secondary were measured to validate the model. With the valid model, the eddy current losses in the secondary were systematically studied in considera-tion of different operating conditions of the LSM, followed by a discussion regarding the influence of cryogenic system on the losses.

The use of metallic sheets as the insulator in a coated superconductor coil is able to increase its turn-to-turn contact resistance for shortening the charging/discharging delay while preserving the self-protection ability. To theoretically understand and predict the properties of the metal-insulation coils, we developed a thermo-electromagnetic model, in which a modified equivalent circuit for electrically representing the metal-insulation coils is built to take the effect of insulator into account. The effectiveness and versatility of this model are verified by different experimental scenarios, e.g., charging, sudden-discharging, and overcurrent. Enabled by the validated model, we carried out a set of case studies and observed that, (a) the metal-insulation coil with a low resistivity and high thermal conductivity metallic insulator is preferable to achieve a better thermal stability; (b) there exists an optimal insulator thickness for realizing the shortest charging delay, but a thicker insulator is superior for realizing a stronger thermal stability; (c) contact resistivity of over 10(4) mu omega center dot cm(2) can weaken the current sharing in the radial direction, which would deteriorate the thermal stability of the metal-insulation coils, although it can significantly suppress the charging delay, implying that a tradeoff is always needed to balance the charging delay and thermal stability when determining the contact resistivity. These findings, mostly being inaccessible from the experiments, provide guidance toward practical applications of metal-insulated coated superconductor coils.