Abstract
Stacks of superconducting (SC) 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 for a 3D model that takes the end effects and real micron-thick SC 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, Jc, 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 Jc into account, 3D calculations agree with measurements with less than a 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.
Highlights
Stacks of superconducting (SC) ReBCO tapes after magnetization behave like permanent magnets but with a superior trapped field, setting the world record of 17.7 T [1] compared to the around 1.3 T maximum remnant magnetic field of conventional permanent magnets
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, Jc, in the direction perpendicular to the tape surface does not play a role in cross-field demagnetization
In this article we focus on the cross-field demagnetization of: stacks of tapes up to 5 tapes with the MEMEP 3D method, the validation of our MEMEP 3D method by comparison of 2 tapes demagnetization with finite element method (FEM), the trapped field in the stack up to 15 tapes, and the qualitative behavior of bulks and stacks with similar parameters
Summary
Stacks of superconducting (SC) ReBCO tapes after magnetization behave like permanent magnets but with a superior trapped field, setting the world record of 17.7 T [1] compared to the around 1.3 T maximum remnant magnetic field of conventional permanent magnets. Trap high magnetic fields (17.6 T [2]), stacks present additional advantages. Their Hastelloy substrate enhances their mechanical properties. Following the critical state model (CSM), a saturated bulk mosaic made of hexagonal or square tiles traps an average flux density of around 1/3 of its maximum, while the average flux density on an stack is around 1/2 of its maximum [4]. A long stack traps 50% more flux than an array of bulks of the same width as the stack for each bulk. The stack enables interlaying sheets of other materials to enhance physical properties: metal layers enhance thermal properties and soft ferromagnetic layers enhance the trapped field and reduce cross-field demagnetization, at least for stacks as stand-alone objects and below the saturation for the magnetic material [5]
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