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Thermo-electromagnetic properties of a magnetically shielded superconductor strip: theoretical foundations and numerical simulations

Ma, G. T. and Rauh, H. (2013):
Thermo-electromagnetic properties of a magnetically shielded superconductor strip: theoretical foundations and numerical simulations.
In: Superconductor Science and Technology, IOP Publishing, p. 105001, 26, (10), ISSN 0953-2048,
[Online-Edition: http://dx.doi.org/10.1088/0953-2048/26/10/105001],
[Article]

Abstract

Numerical simulations of thermo-electromagnetic properties of a thin type-II superconductor strip surrounded by open cavity soft-magnetic shields and exposed to an oscillating transverse magnetic field are performed by resorting to the quasistatic approximation of a vector potential approach in conjunction with the classical description of conduction of heat. The underlying definition of the superconducting constituent makes use of an extended ‘smoothed’ Bean model of the critical state, which includes the field and temperature dependence of the induced supercurrent as well. The delineation of the magnetic shields exploits the reversible-paramagnet approximation in the Langevin form, as appropriate for magnetizations with narrow Z-type loops, and considers induced eddy currents too. The coolant is envisaged as acting like a bath that instantly takes away surplus heat. Based on the Jacobian-free Newton–Krylov approach and the backward Euler scheme, the numerical analysis at hand is tailored to the problem of a high width=thickness aspect ratio of the superconductor strip. Assigning representative materials characteristics and conditions of the applied magnetic field, the main findings for a practically relevant magnet configuration include: (i) an overall rise of the maximum temperature of the superconductor strip tending to saturation in a superconducting thermo-electromagnetic steady state above the operating temperature, magnetic shielding lending increased stability and smoothing the temperature profile along the width of the superconductor strip; (ii) a washing out of the profile of the magnetic induction and a lowering of its strength, a relaxation of the profile of the supercurrent density and an increase of its strength, a tightening of the power loss density and a reduction of its strength, all inside the superconductor strip. The hysteretic ac loss suffered by the superconductor strip is seen to be cut back or, at most, to converge on that of an unshielded strip, thermo-electromagnetic coupling merely playing an insignificant part thereby.

Item Type: Article
Erschienen: 2013
Creators: Ma, G. T. and Rauh, H.
Title: Thermo-electromagnetic properties of a magnetically shielded superconductor strip: theoretical foundations and numerical simulations
Language: English
Abstract:

Numerical simulations of thermo-electromagnetic properties of a thin type-II superconductor strip surrounded by open cavity soft-magnetic shields and exposed to an oscillating transverse magnetic field are performed by resorting to the quasistatic approximation of a vector potential approach in conjunction with the classical description of conduction of heat. The underlying definition of the superconducting constituent makes use of an extended ‘smoothed’ Bean model of the critical state, which includes the field and temperature dependence of the induced supercurrent as well. The delineation of the magnetic shields exploits the reversible-paramagnet approximation in the Langevin form, as appropriate for magnetizations with narrow Z-type loops, and considers induced eddy currents too. The coolant is envisaged as acting like a bath that instantly takes away surplus heat. Based on the Jacobian-free Newton–Krylov approach and the backward Euler scheme, the numerical analysis at hand is tailored to the problem of a high width=thickness aspect ratio of the superconductor strip. Assigning representative materials characteristics and conditions of the applied magnetic field, the main findings for a practically relevant magnet configuration include: (i) an overall rise of the maximum temperature of the superconductor strip tending to saturation in a superconducting thermo-electromagnetic steady state above the operating temperature, magnetic shielding lending increased stability and smoothing the temperature profile along the width of the superconductor strip; (ii) a washing out of the profile of the magnetic induction and a lowering of its strength, a relaxation of the profile of the supercurrent density and an increase of its strength, a tightening of the power loss density and a reduction of its strength, all inside the superconductor strip. The hysteretic ac loss suffered by the superconductor strip is seen to be cut back or, at most, to converge on that of an unshielded strip, thermo-electromagnetic coupling merely playing an insignificant part thereby.

Journal or Publication Title: Superconductor Science and Technology
Volume: 26
Number: 10
Publisher: IOP Publishing
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Materials Modelling
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 28 Aug 2013 10:58
Official URL: http://dx.doi.org/10.1088/0953-2048/26/10/105001
Identification Number: doi:10.1088/0953-2048/26/10/105001
Funders: G T Ma expresses his gratitude to the Alexander von Humboldt Foundation for the award of a Research Fellowship and to the National Science Foundation of China for supplementary financial support (Grant No. 51007076).
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