Abstract
Stacks of superconducting tape can be used as composite bulk superconductors for both trapped field magnets and for magnetic levitation. Little previous work has been done on quantifying the levitation force behavior between stacks of tape and permanent magnets. This paper reports the axial levitation force properties of superconducting tape wound into pancake coils to act as a composite bulk cylinder, showing that similar stable forces to those expected from a uniform bulk cylinder are possible. Force creep was also measured and simulated for the system. The geometry tested is a possible candidate for a rotary superconducting bearing. Detailed finite element modeling in COMSOL Multiphysics was also performed including a full critical state model for induced currents, with temperature and field dependent properties and 3D levitation force models. This work represents one of the most complete levitation force modeling frameworks yet reported using the H-formulation and helps explain why the coil-like stacks of tape are able to sustain levitation forces. The flexibility of geometry and consistency of superconducting properties offered by stacks of tapes, make them attractive for superconducting levitation applications.
Highlights
Stacks of high temperature superconducting (HTS) tapes have proven potential to act as composite superconducting bulks, for either trapped field magnets or as passive components of a magnetic levitation system
Technol. 28 (2015) 115007 levitation, but stacks or blocks made from HTS tape have previously been investigated in the context of maglev applications showing that stable levitation of RE permanent magnets (PMs) is possible [6, 7]
Stable superconducting levitation is possible between PMs and field cooled coils of commercial superconducting tape which could form the basis of a rotary superconducting bearing
Summary
Stacks of high temperature superconducting (HTS) tapes have proven potential to act as composite superconducting bulks, for either trapped field magnets or as passive components of a magnetic levitation system. Recent production of solder coated tape by SuperOx has allowed for the creation of soldered self-supporting slabs with high geometric tolerance, and previous work by the current authors has shown these soldered stacks are well suited to acting as trapped field magnets [8, 9]. The two main advantages of using stacks of commercial HTS tape for superconducting levitation instead of conventional (RE)BCO bulks are (i) predictability and uniformity of the superconducting properties and (ii) flexibility of geometry. The other, planar geometry for superconducting bearings, used in applications like the Boeing flywheel energy storage system [11], involves tessellating hexagonal (RE)BCO bulks to form a planar disk-shaped superconducting stator. The present authors are working on applying stacks of tape to form planar slabs suitable for this type of bearing geometry, to be reported in future publications
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