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

TL;DR

This paper develops 3D models and conducts measurements to accurately predict cross-field demagnetization in superconducting tape stacks, addressing previous modeling limitations by including end effects and anisotropic properties.

Contribution

It introduces a comprehensive 3D modeling approach that accounts for end effects and anisotropic Jc, improving agreement with experimental measurements of demagnetization.

Findings

3D modeling matches measurements within 4% deviation

Perpendicular Jc does not influence cross-field demagnetization

2D models show significantly higher errors

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.