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ISSN: 2772-8307
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cited:7
Critical current density and AC magnetic susceptibility of high-quality FeTe0.5Se0.5 superconducting tapes
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Article Number:Article 100127
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Corresponding email:sunyue@seu.edu.cn; zxshi@seu.edu.cn
Iron telluride-selenium superconducting materials, known for their non-toxicity, ease of preparation, simple structure, and high upper critical fields, have attracted much research interest in practical application. In this work, we conducted electrical transport measurements, magneto-optical imaging, and AC magnetic susceptibility measurements on FeTe0.5Se0.5 superconducting long tapes fabricated via reel-to-reel pulsed laser deposition. Our transport measurements revealed a high critical current density that remains relatively stable even with increasing external magnetic fields, reaching over 1 × 105 A/cm2 at 8 K and 9 T. The calculated pinning force density indicates that normal point pinning is the primary mechanism in these tapes. The magneto-optical images demonstrated that the tapes show homogeneous superconductivity and uniform distribution of critical current density. The AC magnetic susceptibility measurements also confirmed their strong flux pinning nature of withstanding high magnetic field. Based on these characteristics, FeTe0.5Se0.5 superconducting tapes show promising prospects for applications under high magnetic field.
cited:1
Experimental and numerical study of radial and axial HTS magnetic couplers
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Article Number:Article 100128
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Corresponding email:Max.vfk@gmail.com
The paper presents the results of an experimental study and numerical calculations of torques in magnetic couplers of various configurations. A comparison was made for model couplers based on permanent magnets (PMG) and couplers based on high-temperature superconducting (HTS) tapes cooled with liquid nitrogen. In PMG-couplers, both coupler halves are made of permanent magnets, while in HTS-couplers, one coupler half is made of HTS-tapes stacks, and the second of permanent magnets. Both types of couplers are considered in both axial and radial configurations, with different clearances between the coupler halves. The results of experimental studies showed that in the configurations we considered, radial HTS-couplers are superior to their axial analogues in terms of the maximum torque between the coupler halves. In addition, in the considered configurations, PMG couplers exceeded their HTS analogues in torque by 10 times. Numerical finite element calculations using a combined A-T-H formulation were used to optimize the design of the HTS-coupler. The model was verified using the obtained experimental data for moments in model couplers. The model was used to calculate an optimized coupler with added HTS-windings, lower HTS temperature and stronger permanent magnets. The calculation results showed that HTS-couplers can be comparable with their PMG analogues, at the same time they are significantly superior to them in damping external disturbances. Due to the fact that the best characteristics were shown by model radial couplers with minimal gaps between the coupler halves, radial couplers were manufactured based on windings of 10 and 20 layers of HTS-tapes and the torques in them were measured in the FC and ZFC modes. It has been shown that in most operating conditions, 10-layer couplers outperform 20-layer couplers.
cited:18
Design and initial test results of a space-bound flux pump to energize the Hēki mission’s superconducting magnet
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Article Number:Article 100129
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Corresponding email:ben.mallett@vuw.ac.nz
Despite repeated proposals to utilize superconducting magnets in space since at least the 1970s, examples of their use remain scant. One of the technical challenges is to maintain suitable cryogenic temperatures on a spacecraft. This challenge can be alleviated by the use of flux pumps to reduce the required cryogenic cooling power needed to energize the superconducting magnet. This paper describes the design and initial test results of the flux pump to fulfill the requirements of the Hēki mission that will operate a high-temperature superconducting magnet on an external platform of the International Space Station. A transformer-based, self-rectifier architecture was chosen for the flux pump. An effective circuit model used to design its electromagnetic properties and finite-element modelling used in its mechanical and thermal design. Liquid nitrogen tests were used to demonstrate that the electrical performance of the flux pump meets requirements. Higher-fidelity tests using flight-like copies of the hardware and software were undertaken and validated the thermal modelling. These tests also featured the continuous operation of the flux pump in a conduction-cooled setting for over 100 h, reflecting an inherent reliability of this technology. Whilst further testing and flight qualification remains to be completed, we anticipate an on-orbit demonstration of this flux pump technology in April 2025. Such a demonstration will signal a maturing of this emerging superconducting technology for both in-space and terrestrial applications.
cited:22
Numerical study of the effect of anisotropy and field dependence of critical current on AC loss in REBCO coated conductors and stacks
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Article Number:Article 100130
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Corresponding email:dz286@shu.edu.cn; cbcai@t.shu.edu.cn
High-temperature superconducting (HTS) AC electrical devices generally carry AC transport currents and are exposed to AC external magnetic fields with arbitrary orientations. Realistic HTS coated conductors (CCs) show diverse critical current anisotropy and field dependence (Ic(B,)), which directly affect the superconducting behavior. However, under complex electromagnetic (EM) conditions, the discrepancies in AC loss characteristics caused by different Ic(B,) features are still unclear. Moreover, the selection of CCs with desirable Ic(B,) features to further reduce AC loss under various EM conditions remains overlooked. In this work, the transport AC loss (Qt) (without field), magnetization loss (Qm), and total AC loss (Qtot) of the nearly isotropic Shanghai Creative (SCST) CC and the strongly anisotropic Fujikura (FYSC) CC, along with their stacks, are investigated in the range of 90° and 90° (parallel to the CC wide surface) field angles based on the H-formulation. The results show that, due to the opposite angular dependence of Ic, the effective penetration fields of these two CCs or stacks exhibit distinct trends with the field angle, and the Qm in the nearly isotropic CC is less dominated by the perpendicular field component compared to that in the strongly anisotropic CC. Furthermore, due to the different field dependence of Ic at various field angles, the two CCs or stacks exhibit opposite flux flow loss behaviors with the field angle. Overall, the SCST CC and its stack show lower Qtot within the angle range around 0°, and this range expands as the external field increases, while the FYSC CC and its stack show lower Qtot at the remaining angles. This is further explained by analyzing the field distribution and Qtot of each tape in the stacks. This paper clarifies the discrepancies in AC loss caused by different Ic(B,) and identifies the applicable EM conditions for different REBCO materials to reduce AC loss, providing valuable references for material selection to minimize loss in HTS AC devices across different scenarios.
cited:3
Topological versus conventional superconductivity in a Weyl semimetal: A microscopic approach
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Article Number:Article 100132
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Corresponding email:ejmunozt@uc.cl; rodsoto@uc.cl
Starting from a microscopic model for the particle–particle interactions in a Weyl semimetal, we analyzed the possibility for conventional as well as monopole Cooper pairing between quasiparticle excitations at the same (intra-nodal) or opposite (inter-nodal) Weyl nodes. We derived a coupled system of self-consistent BCS-like equations, where the angular dependence of the pairings is directly determined from the microscopic interaction symmetries. We studied the competition between conventional and monopole superconducting phases, thus obtaining explicitly the phase diagrams from the microscopic interaction model parameters. We determined the critical temperatures for both phases, and the low temperature critical behavior, including the specific heat, that we suggest as possible experimental probe for topological quantum criticality in Weyl semimetals.
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