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ISSN: 2772-8307
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cited:13
Electromagnetic modeling, loss analysis, and stress evaluation of parallel-wound no-insulation high-temperature superconducting magnets
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Article Number:Article 100217
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Abstract
Corresponding email:qiuliang@mail.iee.ac.cn；liujianhua@mail.iee.ac.cn
The parallel-wound technique is an effective method for reducing charging delay and enhancing electromagnetic margin of no-insulation high-temperature superconducting (NI HTS) coils, as demonstrated by both experiments and numerical simulations. From an engineering standpoint, the parallel-wound design also mitigates the constraint of individual conductor length, which is a significant limitation in large-scale coils requiring a single continuous conductor of the same specifications. However, traditional electromagnetic modeling of parallel-wound no-insulation (PWNI) HTS coils relies on equivalent circuit models, and a combined finite element model is required to capture the screening current characteristics of HTS coated conductors. The mutual invocation between circuit models and finite element models increases the technical demands on simulation engineers and complicates the analysis of electromagnetic interactions with other physical fields. To address these challenges, we first propose an axisymmetric distributed equivalent circuit model for PWNI HTS double pancake (DP) coils. The equivalent circuit model is then integrated directly into the finite element framework of T-A formulation, resulting in a streamlined electromagnetic finite element model. The validity of this model is confirmed through the charging and discharging experiments with a dual-wound NI HTS coil. Utilizing this model, we further investigate the effects of joint resistance and turn-to-turn contact resistivity on the electromagnetic characteristics of PWNI HTS coils. Additionally, the excitation loss and stress of multiple PWNI HTS DP coils in a 35 T all-superconducting high field magnet are also analyzed. The results indicate that both the lower turn-to-turn contact resistivity and joint resistance may lead to significant non-uniform currents within the coil. The joint resistance has a significant impact on the critical current of PWNI HTS coils, and the optimization of energization methodology increased the critical current of the experimental coil by 12 A. Enhancing the equivalent radial resistance between bundled turns proves more effective for reducing charging delay of PWNI coil than increasing that within bundled turns. Multiple PWNI coils in high field magnet exhibit elevated losses relative to single-tape equivalents due to coupling currents, particularly during the initial excitation. However, their peak strain accumulation is marginally lower than that of single-wound configuration.
Abstract
Corresponding email:liumingxin20@nudt.edu.cn；lofter@163.com；jieli@nudt.edu.cn
Superconducting electrodynamic suspension (EDS) systems generate the required propulsion, levitation, and guidance forces for vehicle motion through electromagnetic interactions between ground coils and onboard superconducting coils. The propulsion coils (providing propulsion force) and the null-flux coils (providing levitation and guidance forces) are typically installed separately. In the 1980s, an integrated Propulsion-Levitation-Guidance (PLG) coil was proposed to reduce the number of ground coils and lower system costs, combining all three functional requirements into a single coil design. Visually resembling conventional null-flux coils in appearance, the PLG coils are distinguished by their active three-phase alternating current (AC) excitation. However, extensive research and experimental studies revealed that PLG coils exhibit significant propulsion force fluctuations, which not only increase control complexity in the propulsion system but also adversely affect the maintenance of the superconducting state of the superconducting coils. This paper presents an improved PLG system design featuring a double-layer coil configuration, which achieves significant reduction in propulsion force fluctuations without increasing material costs. A comprehensive theoretical model is developed for the fully coupled dynamic circuit, explicitly incorporating mutual inductance coupling between adjacent PLG coils. The model's validity is rigorously verified through comparison with experimental data obtained from the Miyazaki test line. Based on the structural parameters of the PLG coils in the Miyazaki test line, this paper presents the structural parameters of the double-layer PLG coils. Through comparative analysis of the theoretical electromagnetic force characteristics between the two kinds of coil structures, the superior performance of the double-layer PLG coils is confirmed.
Abstract
Corresponding email:jld35@cam.ac.uk
The factors that influence high-field, low-temperature current carrying performance of coated conductors are complex. Using epitaxial thin films grown by pulsed laser deposition (PLD) made from (RE’RE”)Ba2Cu3 O (YREBCO), where RE = rare earth targets, with and without liquid (L) additions, this work decouples the different complex effects (both positive and negative) of RE mixing. In doing so, we understand the outcomes of the separate effects of this mixing, and the incidental formation of (Y,RE’,RE”)2O3 nanoparticles. The YREBCO composition is chosen because it permits growth conditions to be the same and near-optimum for all the targets, i.e., at the optimum temperature as for the growth of pure YBCO, the reference composition, to enable effective comparison of compositions. We find that a high RE ion size variance increases the RE2O fraction but that (20 K, 8 T) is decreased, owing to the associated atomic disorder. On the other hand, we find that for moderate variance (and moderate RE2O3 nanoparticle formation), (20 K, 8 T) is increased. A liquid phase needs to be included to ensure minimal microstructural disorder of the YREBCO lattice caused by the RE2O nanoparticle inclusions. Of the wide range of PLD target compositions explored, (GdYb)Ba2Cu3O is determined to have the optimum moderate ion size variance. An approximate doubling of (20 K, 8 T) compared to pure YBCO films results. Thus, the (GdYb)Ba2Cu3O composition with extra liquid phase addition represents an ideal base composition to which artificial pinning centres (APC) can be added for further enhancement.
cited:0
Anisotropy modulation and band structure reconstruction induced by high pressure in Kagome metal GdV6Sn6
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Article Number:Article 100174
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Abstract
Corresponding email:yangxiaofan@fudan.edu.cn
The geometric frustrations and unique electronic structures in Kagome lattices normally give rise to various quantum matter ground states. V-based Kagome compounds, such as AV3Sb5, exhibit a complex phase diagram under hydrostatic pressure modulation. Herein, we report an electronic structure evolution in another novel V-Kagome system RV6Sn6, with pressures changing from 0 to 107 GPa, through density functional calculations. Our results reveal that the electronic density of GdV6Sn6 exhibits pronounced anisotropy under high pressures. Specifically, electronic structure instabilities stem from van Hove singularities are observed in the V-Kagome plane, while that remains robust up to approximately 40 GPa in the M momentum space. In the high-pressure regime (107 GPa), the newly formed saddle point approaches and crosses the Fermi level, enhancing the density of states (DOS) at the Fermi level. This potentially results in pressure-induced superconductivity, accompanied by the formation of charge channels. Our findings provide essential insights into the electronic structure of GdV6Sn6 under high pressures, offering a valuable model for investigating V-Kagome physics in RV6Sn6 compounds.
cited:8
High critical current double-sided, thick-film REBa2Cu3O7−δ tapes by Advanced MOCVD
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Article Number:Article 100184
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Abstract
Corresponding email:tmqu@mail.tsinghua.edu.cn
Enhancing the cost-effectiveness and performance of Rare Earth Barium Copper Oxide (REBCO) coated conductors remains a key objective for advancing applications in power transmission, fusion energy, particle accelerators, and rotating machines. One direct method to achieve this is by increasing the conductor’s critical current under operational conditions. This study introduces a major breakthrough in fabricating Zr-doped (Gd,Y) BaCuO double-sided tapes utilizing an Advanced Metal Organic Chemical Vapor Deposition (A-MOCVD) technique. A single-pass deposition resulted in uniform films of on both sides of the tape, with critical current values at 20K and 20T consistently above 950 A/4 mm, peaking at 1100 A/4 mm. Additionally, a self-field transport critical current of 930 A/4 mm was attained in self-field conditions at 77 K, 0 T, translating to a critical current density of 2.9 MA/cm 2. These results represent some of the highest reported performance metrics for REBCO tapes of this thickness, underscoring the potential of double-sided A-MOCVD processing for next-generation superconducting applications.
cited:9
Critical current degradation of REBCO coated conductor tapes caused by multiple cracks under tensile loading
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Article Number:Article 100185
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Abstract
Corresponding email:tmqu@mail.tsinghua.edu.cn
REBa2Cu3Ox (REBCO) coated conductors exhibit irreversible critical current () degradation under tensile strain beyond the irreversible strain (). While this degradation is attributed to cracking, the specific crack evolution process and its quantitative relation to degradation remain unclear. Here, the multiplication of cracks in REBCO tapes under tensile is characterized. It was found that surface particles disrupt continuous crack propagation, causing fragmentation of the REBCO layer. A shear lag model describes how the stress distribution evolves with fragmentation spacing. A probabilistic fracture model then predicts the two-regime spacing reduction as a function of applied strain. The discontinuous crack network acts as the residual flow channel for current once strain exceeds . Crack spacing determines the remaining in this regime. An analytical model is thus proposed to capture the degradation behavior based on the quantified fragmentation process. Additionally, this study suggests approaches to obtain a wider safe operating strain range through tailoring of the fracture behavior, expanding the practical application limits. This work provides new insights into the progressive cracking mechanisms governing irreversible degradation in strained REBCO tapes.
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