Bulk trapped-field superconducting magnets arranged in a linear Halbach array: important points to achieve the full potential of the magnetized superconductors (invited)

Bulk superconductors can act as very powerful permanent magnets, referred to as trapped-field superconducting magnets. These superconducting magnets can generate magnetic field gradients much larger than those typically achievable with conventional ferromagnetic materials [1]. This property is exploited for generating remotely a magnetic force in a number of engineering applications including magnetic separation or magnetic drug delivery [2]. Arranging trapped-field superconducting magnets with mutually perpendicular magnetization directions allows one to make a linear Halbach array. Building such arrays opens the prospect of generating magnetic field gradients exceeding significantly those generated by a single superconductor. One of the main challenges in achieving this goal is to ensure that the superconductors remain fully magnetized during the assembly process of the array [3]. In this communication, different solutions are described and compared to overcome the demagnetization of the trapped-field superconducting magnets. We consider either taking advantage of an additional superconductor removed at 90° from the axis of the array [4], using bulk superconductors with triangular cross-section or creating a vertical offset between the central and peripheral samples. Experimental results are presented on a linear array made of three magnetized bulk large grain melt-textured YBa2Cu3O7-δ superconductors at 77 K. The experimental spatial distribution of the magnetic flux density above the assembly is compared to analytical calculations and finite-element simulations. In addition, arrangements involving non-cubic superconductors are characterized using a bespoke cryogenic 3-axis Hall probe [5]. We show how the various solutions modify the distribution of the magnetic flux density at reasonable distance from the assembly while ensuring a minimal demagnetization effect. By examining the ‘useful’ spatial zone where the magnetic field gradient exceeds a given threshold (e.g. 1 T/m), it is possible to obtain array configurations for which the extension of the useful zone is significantly larger than that of a single magnetized superconductor.
References
1. J. H. Durrell et al., Supercond. Sci. Technol. 31 103501 (2018)
2. A. Arsenault et al, IEEE Trans. Appl. Supercond. 33 4401409 (2023)
3. M. Houbart et al., Supercond. Sci. Technol. 35 064005 (2022)
4. M. Houbart et al., Supercond. Sci. Technol. 36 115012 (2023)
5. N. Rotheudt et al., Cryogenics 103693 133 (2023)