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August, 2018

High temperature superconducting (HTS) tape can be cut and stacked to generate large magnetic fields at cryogenic temperatures after inducing persistent currents in the (RE)BCO superconducting layers. This allows them to act as permanent magnets capable of generating much higher fields than conventional rare-earth magnets. A field of 17.7 T was trapped between two stacks of HTS tape at 8 K with no external mechanical reinforcement. The superalloy substrates support enormous tensile stresses the thin and brittle HTS layer experiences. A new type of hybrid stack was used consisting of a 12 mm square insert stack embedded inside a larger 34.4 mm diameter stack made from different tape. The magnetic field generated is higher than the previous trapped field record achieved by a bulk HTS magnet and 30% greater than previously achieved in a stack of HTS tapes. Such stacks are being considered for superconducting motors as rotor field poles where the cryogenic penalty is justified by the increased power to weight ratio (EU project ASuMED). The sample reported can be considered the strongest permanent magnet ever created.

Figure caption: Composition and geometry of the hybrid stack of superconducting tape acting as a composite superconducting permanent magnet. It consists of a 12 mm square stack made from SuperPower tape inside a larger cylindrical stack made from American Superconductor tape.

A. Patel, A. Baskys, T. Mitchell-Williams, A. McCaul, W. Coniglio, J. Hänisch, M. Lao and B. A. Glowacki, "A trapped field of 17.7 T in a stack of high temperature superconducting tape", Supercond. Sci. Technol. 31 (2018) 09LT01