cited:0

Foreword

Article Number:Article 100001 Author:Shi-Xue Dou (窦士学) , Zhijian Jin (金之俭) , Jiangang Li (李建刚) , Zhongqin Lin (林忠钦) , Xiaoming Xie (谢晓明) , Qiuliang Wang (王秋良) Article preview
Abstract

Superconducting materials have attracted extensive attention of scientists around the world thanks to their unique physical properties. The worldwide research focuses on the fundamental frontier to explore novel superconducting materials and even room-temperature superconductors with higher superconducting transition temperature. In recent years, significant progresses have been achieved in such fundamental frontier study of superconductivity. The superconductivity of magic-angle graphene was discovered in 2017 and lanthanum hydride room temperature superconductor was discovered in 2019, which has aroused widespread attention and great sensation. On the other hand, research also addresses challenges associated with superconducting applications. Lately, key breakthroughs have been made in the development of cutting-edge technologies that function upon superconductivity, such as smart grid, compact fusion reactor, high-speed magnetic levitation, particle medicine, superconducting ultra-high sensitivity detector, and superconducting chip. This sets off a new round of upsurge for superconducting materials in the world.


In-depth integration across multiple disciplines is the key trend in superconducting application research. The development of superconducting technologies will bring revolutionary breakthroughs in many essential areas. The birth of Superconductivity Journal will contribute to exchange of information between fundamental and applied researches on innovative superconducting technologies and strengthen the aggregation effect of high-standard superconducting researches. The journal will keep forging ahead, create a world-class academic journal in the field of superconductivity, and promote the development of superconductivity technology.


超导材料以其独特的电磁特性吸引着世界范围内科学家们的广泛关注。超导研究一方面聚焦于基础前沿, 探索具有更高超导转变温度的超导材料乃至室温超导体。近年来超导前沿基础研究不断获得新进展, 2017年发现了魔角石墨烯的超导特性, 2019年发现了氢化镧室温超导体, 都引起了广泛的关注和巨大的轰动。另一方面, 超导研究又侧重技术应用, 近年来智能电网、可控核能源、高速磁悬浮、粒子医疗、超导超高灵敏探测器和超导芯片等前沿技术研究不断取得关键突破, 在全球掀起新一轮热潮。

多学科的交叉深度融合是超导应用技术发展的趋势, 超导技术的发展必将带来多个重要领域变革性的技术突破。《Superconductivity》期刊的诞生将有助于创新性超导技术相关的基础与应用研究交流, 加强超导高水平研究的聚集效应。本期刊将不断进取, 打造超导领域的国际一流学术期刊, 推动超导技术的发展。
Review
cited:92

Electromagnetic-thermal-structure multi-layer nonlinear elastoplastic modelling study on epoxy-impregnated REBCO pancake coils in high-field magnets

Article Number:Article 100002 Corresponding Author: Xingzhe Wang Author:Peifeng Gao, Mingzhi Guan, Xingzhe Wang, Youhe Zhou Article preview
Abstract
The elastoplastic mechanical behaviour of an epoxy-impregnated REBCO pancake winding under cryogenics and high magnetic field is investigated in the frame of finite element (FE) modelling. A two-dimensional axisymmetric electromagnetic-thermal-structure multi-physics multi-layer FE model with main layers of the coated conductor and insulation materials is developed. The radial stress and hoop stress on each constituent layer induced by thermal mismatch stress during cooling are investigated. The mechanical behaviour of each constituent material is also analysed by considering the thermal mismatch stress and electromagnetic force under 20 T background field. The results show that discrete stresses appear in all the constituent materials indicating that the multi-layer winding model containing the main constituent materials is necessary for the accurate stress analysis in an epoxy-impregnated REBCO winding. The stress of each constituent material induced by thermal mismatch during cooling process are too high to be ignored in the subsequent electromagnetic structure analysis. The mechanical-magnetic coupling analyses show that the stresses of all the constituent materials increase with the transport current. The plastic failure mainly induced by hoop stress successively occurs on copper stabilizer and Hastelloy substrate of the innermost turn, and the plastic region propagates from the inner turns to the outer turns with the increase of transport current. The failure of the superconducting layer occurs before the yield in Hastelloy due to the direct action of Lorentz force on the superconducting layers. The transverse tensile stress increases with the increasing transport current, indicating that the risk of transverse delamination failure increases with the increase of transport current. The mechanical failure modes including delamination within the conductor, plastic deformation in substrate and crack in superconducting layer should be seriously considered.
Review
cited:28

Superconducting fault current limiter (SFCL) for fail-safe DC-DC conversion: From power electronic device to micro grid protection

Article Number:Article 100003 Corresponding Author: Boyang Shen Author:Xiaoyuan Chen, Mingshun Zhang, Yu Chen, Shan Jiang, Huayu Gou, Yi Lei, Boyang Shen Article preview
Abstract
In DC micro grids and networks, DC-DC power converters having a large number of semiconductor-based power electronic devices are usually adopted to interconnect the renewable sources and flexible loads. Most of the semiconductor-based devices suffer from poor fault withstanding abilities, but conventional power electronic protection schemes have the bottlenecks of the time-delay, self-malfunction and mis-judgement. This paper presents a novel solution using the superconducting fault current limiter (SFCL) to protect a power electronic device and extend the usage to a micro grid. This SFCL is actually a self-triggering, recoverable, and passive current limiter, which does not involve any additional circuit hardware and software. Experimental investigations and simulation analyses clarify the feasibility of using this superconductor-based protection scheme to implement the self-acting fail-safe protection of DC-DC converters. Further system-level simulations explore the SFCL to suppress the over-current and stabilize the bus voltage of a photovoltaic based DC micro grid, particularly facing millisecond-level transients and faults. Our experimental and theoretical investigations lay some technical bases to establish a superconductor-semiconductor-coupled interdisciplinary application from the view from the applied superconductivity, to power electronics, and to micro grids.
Review
cited:6

China’s participation in the international RRT for Ic measurement of superconducting cables organized by IEC/TC90

Article Number:Article 100004 Corresponding Author: J. Li Author:J. Li, Y. Shi, G.M. Zhang, L.W. Jing, J.X. Zheng, C.L. Liu, W. Yuan, Y.S. Wang, M. Song, Y.J. Xia, X.H. Zong, Y.W. Han, D.N. Zheng, X.J. Zhou, T. Matsushita, G. Nishijima Article preview
Abstract
Currently, IEC/TC90 is working on standardizing the method for measuring critical current (Ic) in superconducting cables. At the end of 2020, an international round robin test (RRT) was organized, in which five Chinese institutions participated, and four accomplished the test. The electric-field versus current (E-I) curves obtained by each institution are highly repeatable. Those obtained by different institutions are nearly identical after appropriate curve averaging, indicating high reproducibility, except the last participant's inner core curves. The discrepancy was later determined to be the result of sample cable damage. After excluding highly deviated data, it is determined that the maximum relative standard uncertainty in Ic is 0.7%, and the maximum relative standard uncertainty in n-value is 12.8%. The Ic values are comparable to Japan's domestic RRT results, but the n-values are significantly different. The test results support the DC four-terminal method as a recommended test method, with a target relative uncertainty of less than 2% for the Ic value.
Review
cited:27

Engineering-based design and fabrication procedure for mid-temperature REBCO magnets accommodating the strong Ic anisotropy

Article Number:Article 100005 Corresponding Author: Qiuliang Wang, Lei Wang Author:Zili Zhang, Benzhe Zhou, Jianhua Liu, Lei Wang, Qiuliang Wang Article preview
Abstract
An engineering-feasible design and fabrication procedure for REB2aCu3O7-x (REBCO) magnets based on the strong Ic angle dependence at moderate temperatures (40–77 K) was developed. In this procedure, the Ic value of every REBCO coil of the magnet is calculated from the Ic (B,θ) data of REBCO tape at operating temperature with different applied fields, which is called the “full field-angle dependent Ic method.” This approach has significantly higher accuracy than the conventional method, which only focuses on the Ic value at the coil with the highest perpendicular field component. Additionally, the fitted lift factor at 45 K with different applied fields was closely related to the minimum Ic value at 77 K and 0.5 T. The engineering-feasible design and fabrication procedure for the REBCO magnet was developed on the basis of the Ic values calculated via the “full field-angle dependent Ic method” and lifting-factor fitted method, and it had a design error of <5%. The proposed technique is a more accurate method for the design and fabrication of cooling REBCO coils and will improve the applicability of REBCO magnets in this temperature range.
Review
cited:17

Geometric origin of intrinsic dark counts in superconducting nanowire single-photon detectors

Article Number:Article 100006 Corresponding Author: Lixing You Author:Xingyu Zhang, Xiaofu Zhang, Jia Huang, Can Yang, Lixing You, Xiaoyu Liu, Peng Hu, You Xiao, Wenying Zhang, Yongliang Wang, Lingyun Li, Zhen Wang, Hao Li Article preview
Abstract
The dark count is one of the key physical issues for superconducting nanowire single-photon detectors (SNSPDs) that limits various applications for optical quantum information and classical optics. When the bias current approaches the switching current of SNSPDs, the dark count is actually dominated by the intrinsic dark counts (iDCs). However, the origin of iDCs and its relation to constrictions remains unclear for practical SNSPDs. We herein systematically characterize the iDCs of the SNSPDs with and without artificial geometric constrictions by applying the differential readout method. For these devices with constrictions, we have observed distinct Gaussian distributions in the temporal distribution of iDCs, in which the time difference between the distributions is consistent with the geometric distance between constrictions, and the rates of iDCs produced by each constriction are in good agreement with constrictions' widths. With respect to practical SNSPDs, surprisingly, we also observe several Gaussian distributions in the temporal domain and it shows no significant dependence on the devices’ sizes, demonstrating that the iDCs of SNSPDs are mainly dominated by a few specific constrictions.
Review
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