[WBP2] Bulk, Assembled Conductors, AC Loss

[WBP2-27] Interest of bulk MgB₂ superconductor for magnetic levitation applications

*Jacques NOUDEM¹, Yiteng XING¹, Pierre BERNSTEIN¹ (1. Université de Caen Normandie, ENSICAEN, CNRS UMR 6508 CRISMAT, Normandie Univ., 14000 Caen (France))

Keywords:

MgB₂ bulk material,Superconducting Maglev,Levitation,Guidance force

Superconducting Magnetic levitation system (SML) is widely used for some promising applications of superconductors, especially Maglev trains and superconducting bearings. The levitation force and its stability are closely related to the superconducting material, the system generating the magnetic field and their geometrical dimensions. The simple fabrication process of large-size MgB₂ bulks with a levitation force similar to that of the superconducting cuprates [1] shows the enormous potential of this material for magnetic suspension device applications. This study investigates the effects of various factors on the levitation and lateral forces in a system consisting of a cylindrical NdFeB permanent magnet and MgB₂ bulk: i) dimensions of the superconductor, ii) the working temperature and iii) the cooling height. Three batches of samples were prepared by the Spark Plasma Sintering (SPS) [2] process using MgB₂ powder purchased from Pavazyum company (Turkey). The first batch consisted of cylindrical bulks with a 50 mm diameter, and the thicknesses, h_SC, ranged from 2 mm to 16 mm. The second batch consisted of 10 mm thick bulks with diameters, D_SC, ranging between 50 mm and 70 mm, while the third batch included a large-size sample with a diameter of 120 mm and a thickness of 6 mm. The magnetic force measurements were carried out at 20-30 K in a vacuum cryostat system that allows measuring forces down to a very low separation between the magnetic source and the superconductor. The results have shown that the levitation force, F_Z increases with the sample diameter and that there is a linear relation between F_Z and D_SC³ as indicated in [1]. Otherwise, the levitation forces do not depend on the thickness h_SC of the samples above some threshold and are slow varying functions of h_SC below the threshold. Furthermore, the loss of stability corresponds to the positive stiffness of lateral force. The results suggest that the stability of the system could be optimized using a large size superconductor and a small size permanet magnet. Concerning the effect of working temperature, stability can be significantly improved by increasing the temperature from 28 to 30 K, but that this causes a decrease of the levitation force as a consequence of the reduction of the critical current density J_c. In addition, a remarkable magnetic levitation force up to 700 N at 20 K was achieved with the 120 mm diameter MgB₂ bulk and the levitation being stable up to levitation forces exceeding 400 N. As a consequence, with the ongoing advancements in large-scale MgB₂ fabrication techniques and the development of liquid hydrogen technology [3], large-size MgB₂ bulk can be considered as one of the best choices for future superconducting magnetic levitation systems.

Reference [1] Bernstein P and Noudem J 2020 Superconducting magnetic levitation: principle, mate- rials, physics and models Supercond. Sci. Technol. 33 033001[2] Noudem J G, Xing Y, Bernstein P, Retoux R, Higuchi M, Arvapalli S S, Muralidhar M and Murakami M 2020 Improvement of critical current density of MgB2 bulk supercon- ductor processed by Spark Plasma Sintering Journal of the American Ceramic Society 103 6169–75[3] Mojarrad M, Farhoudian S and Mikheenko P 2022 Superconductivity and Hydrogen Economy: A Roadmap to Synergy Energies 15 6138