IOP : Cross-field demagnetization of stacks of tapes: 3D modeling and measurements

Kapolka, Milan; Baskys, Algirdas; Dadhich, Anang; Climente-Alarcon, Vicente; Glowacki, Bartek A.; Grilli, Francesco; Pardo, Enric

doi:10.1088/1361-6668/ab5aca

Published Articles
Report number	arXiv:1909.12129
Title	Cross-field demagnetization of stacks of tapes: 3D modeling and measurements
Author(s)	Kapolka, Milan (Bratislava, Electrotech. Inst.) ; Pardo, Enric (Bratislava, Electrotech. Inst.) ; Grilli, Francesco (KIT, Karlsruhe) ; Baskys, Algirdas (Cambridge U. ; CERN) ; Climente-Alarcon, Vicente (Cambridge U.) ; Dadhich, Anang (Bratislava, Electrotech. Inst.) ; Glowacki, Bartek A. (Cambridge U. ; Inst. Power Eng., Warsaw)
Publication	2020-03-13
Imprint	2019-09-26
Number of pages	15
Note	36 pages, 20 figures
In:	Supercond. Sci. Technol. 33 (2020) 044019
DOI	10.1088/1361-6668/ab5aca
Subject category	physics.app-ph ; cond-mat.supr-con
Abstract	Stacks of superconducting tapes can trap much higher magnetic fields than conventional magnets. This makes them very promising for motors and generators. However, ripple magnetic fields in these machines present a cross-field component that demagnetizes the stacks. At present, there is no quantitative agreement between measurements and modeling of cross-field demagnetization, mainly due to the need of a 3D model that takes the end effects and real micron-thick superconducting layer into account. This article presents 3D modeling and measurements of cross-field demagnetization in stacks of up to 5 tapes and initial magnetization modeling of stacks of up to 15 tapes. 3D modeling of the cross-field demagnetization explicitly shows that the critical current density, $J_c$, in the direction perpendicular to the tape surface does not play a role in cross-field demagnetization. When taking the measured anisotropic magnetic field dependence of $J_c$ into account, 3D calculations agree with measurements with less than 4 % deviation, while the error of 2D modeling is much higher. Then, our 3D numerical methods can realistically predict cross-field demagnetization. Due to the force-free configuration of part of the current density, J, in the stack, better agreement with experiments will probably require measuring the Jc anisotropy for the whole solid angle range, including $J$ parallel to the magnetic field.
Copyright/License	CC-BY-3.0

$\R{The measurement set-up magnetizes the superconducting stack by field cooling using an electromagnet and later applies alternating cross-field demagnetization by means of a copper coil.}$ $\R{The modeling results of cross-field demagnetization are mesh independent for the used mesh of $15\times 15\times 9$ elements in each tape. Results above for a single tape with several number of cells in the thickness, ripple field of 240 mT amplitude and 500 Hz frequency, 10 cycles of ripple field, and field cooling process shown in figure \ref{wave_form.fig} followed by 900 s of relaxation. Cross-field demagnetization starts at time 1000~s.}$