Shielding the stray magnetic field of a large superconducting coil from a rotating machine: Experimental demonstration of scalable screens combining bulk superconductors and coated conductors (invited)

Conventional rotating machines use a ferromagnetic structure to enclose the magnetic field lines and protect sensitive equipment and human operators. However, next-generation, superconductor-based rotating machines aim to increase the power density in several applications (e.g., electric aircraft or floating offshore wind turbine) [1,2], thereby reducing the weight and/or enabling operation at higher fields and, consequently, removing or reducing the ferromagnetic structure. New ways must therefore be found to attenuate the high, low-frequency, inhomogeneous stray magnetic field over wide surface areas. In our previous works, we demonstrated that closed-loop coated conductors can be placed around a bulk superconductor to improve its magnetic screening/shielding properties [3,4]. In this work, we introduce a new topology made of four 60 mm-diameter disk-shaped bulks arranged side-by-side. Closed-loop coated conductors are interleaved around them and short stack tape segments are added. The resulting structure is subjected (at 77 K) to the inhomogeneous stray magnetic field (up to ~150 mT) of a large superconducting coil designed to demonstrate a rotating machine pole of a direct-drive wind turbine. The key findings are as follows. First, adding the loops around the bulks is a lightweight and effective
way to mitigate the presence of the gaps between the bulks (one of the main problems in building large screens). The role of these loops is also confirmed by trapped field measurements. Second, the screened surface area is, consequently, substantially increased and suitable field attenuations are obtained at low fields over at least 138 mm. Third, analysing the measurements in terms of axial and transverse components of the field help us explain the influence of the inhomogeneity of the applied field on the screening properties.
References 1. A. B. Abrahamsen et al 2010 Supercond. Sci. Technol. 23 034019
2. Y. Terao et al 2019 IEEE Trans. Appl. Supercond. 29(5), 5202305
3. N. Rotheudt et al 2024 Supercond. Sci. Technol. 37 065008
4. N. Rotheudt et al 2025 Supercond. Sci. Technol. 38 025012