Thickness Dependence of Trapped Magnetic Fields in Machined Bulk MgB2 Superconductors

被引:8
作者
Ainslie, M. D. [1 ]
Yamamoto, A. [2 ,3 ]
机构
[1] Univ Cambridge, Dept Engn, Bulk Superconduct Grp, Cambridge CB2 1PZ, England
[2] Tokyo Univ Agr & Technol, Dept Appl Phys, Koganei, Tokyo 1848588, Japan
[3] Tokyo Inst Technol, Mat Res Ctr Element Strategy, Yokohama, Kanagawa 2268503, Japan
基金
英国工程与自然科学研究理事会;
关键词
Machining; Magnetic field measurement; Superconducting magnets; Mathematical models; Magnetic fields; Superconductivity; Magnetization; Bulk MgB2; H-formulation; numerical modelling; trapped field magnets; thickness dependence;
D O I
10.1109/TASC.2022.3147140
中图分类号
TM [电工技术]; TN [电子技术、通信技术];
学科分类号
0808 ; 0809 ;
摘要
MgB2 in bulk form shows great promise as an inexpensive, lightweight alternative to bulk (RE)-Ba-Cu-O materials to act as trapped field magnets (TFMs), which can replace permanent magnets in applications such as desktop high-field magnet systems and rotating machines. In this paper, we investigate the thickness dependence of the trapped magnetic field in bulk MgB2 superconductors. Two bulk MgB2 samples, 20 mm in diameter and 10 mm in thickness, were fabricated using the powder-in-closed-tube (PICT) technique. The trapped field was then measured after field-cooled magnetisation for thicknesses of approximately 20 mm (both bulks stacked), 10 mm (single bulk), and then 7.5, 5, 4, 3, 2, 1.5 and 1 mm, for which the sample was machined down to the designated thickness using an automated-wet-polishing technique. A 2D axisymmetric finite-element model based on the H-formulation is used to simulate the experimental results and explain the observed thickness dependence of the trapped field. The numerical results assume a J(c)(B) dependence based on the measured characteristics of small specimens taken from the bulk before and after machining. The J(c)(B) measurements suggested a degradation of J(c) occurred as the bulk was machined thinner and thinner: a decrease in J(c)(0 T) of similar to 35% was observed between the pre- and post-machining specimens. Taking this into account in the models, by assuming a linear reduction in J(c) with each machining process, reproduced the experimental results with very good agreement. Consistent trapped field measurements on the top and bottom surfaces suggest this degradation occurred globally, rather than local to the machined surface.
引用
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页数:4
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