sust SUSTEF Superconductor Science and Technology SUST Supercond. Sci. Technol. 0953-2048 1361-6668 IOP Publishing sustab66e7 10.1088/1361-6668/ab66e7 ab66e7 SUST-103571.R1 Paper Focus on Processing and Application of Superconducting Bulk Materials 2019 Flux jumps in ring-shaped and assembled bulk superconductors during pulsed field magnetization Flux jumps in ring-shaped and assembled bulk superconductors during pulsed field magnetization Zhou Difan 1 2 3 0000-0001-9889-8872 Shi Yunhua 2 0000-0003-4240-5543 Dennis Anthony R 2 Cardwell David A 2 0000-0002-2020-2131 Durrell John H 2 0000-0003-0712-3102 Shanghai Key Laboratory of High Temperature Superconductors, Department of Physics, Shanghai University, Shanghai 200444, People’s Republic of China Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, United Kingdom dz286@shu.edu.cn

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3 2020 20 01 2020 20 01 2020 33 3 034001 13 10 2019 12 12 2019 02 01 2020 13 10 2019 © 2020 The Author(s). Published by IOP Publishing Ltd 2020 Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Abstract

Bulk (RE)BCO, where RE is a rare-earth element or yttrium, superconductors fabricated in the form of rings are potentially useful for a variety of solenoidal-type applications, such as small, high field nuclear magnetic resonance and electromagnetic undulators. It is anticipated that the practical exploitation of these technologically important materials will involve pulse field magnetization (PFM) and, consequently, it is important to understand the behavior of ring-shaped samples subjected to the PFM process. Macroscopic flux jumps were observed in PFM experiments on ring-shaped bulk samples when the peak applied field reaches a threshold magnitude, similar to behavior reported previously in cylindrical samples. Magnetic flux jumps inward when the thermal instability is triggered, however it subsequently flows outwards from the sample, resulting in a relatively low trapped field. This behavior is attributed to a variety of effects, including the inhomogeneity of the material, which may lead to the formation of localized hot spots during the PFM process. In order to further elucidate this phenomena, the properties of a structure consisting of a bulk superconducting ring with a cylindrical superconductor core were studied. We observe that, although a flux jump occurs consistently in the ring, a critical state is established at the boundary of the ring-shaped sample and the core. We provide a detailed account of these experimental observations and provide an explanation in terms of the current understanding of the PFM process.

HTS bulk superconductors magnetization trapped field flux dynamics flux jump Engineering and Physical Sciences Research Council https://doi.org/10.13039/501100000266 EP/P00962X/1 ccc 0953-2048/20/034001+7$33.00 printed Printed in the UK crossmark yes