Behaviour of neighbouring bulk trapped field magnets with parallel or orthogonal magnetizations

This presentation deals with the behaviour of bulk superconductors used as trapped-field permanent magnets. We investigate the situation where the bulk superconductors are first magnetized permanently and then brought next to each other, in view of generating a large magnetic flux density gradient. We first consider the approach of bulk cylindrical superconductors with parallel axial magnetizations, either along their symmetry axis (i.e. the translational motion is parallel to their axis) or sideways (i.e. the motion is perpendicular to their axis) [1]. We show that repeated approach / separation cycles yield an irreversible behaviour that can be reproduced qualitatively using a simple analytical model. Next, we consider the assembly of three cuboid bulk superconductors with orthogonal magnetization directions. Experimental results are obtained for bulk YBCO superconductors (~ 14 mm side) pre-magnetized independently and brought in close vicinity using a computer-controlled motor capable of overcoming the repulsive force between them. Experimental results show that the approach of the magnetized superconductors leads to a redistribution of the current density in the central superconducting sample during the approach. This phenomenon can be reproduced correctly using a simple analytical model. We also compare the results obtained with trapped field superconductors to those obtained with permanent magnets.
Reference :
[1] M Houbart et al. Supercond. Sci. Technol. 33 064003 (2020).