Speaker
Description
Investigations carried out up to now on superconducting Maglev trains have always planned to use YBCO or REBCO oxides as superconducting materials [1, 2]. While MgB2 enters more and more applications [3], bulk MgB2 has not yet been seriously considered for Maglev projects. Its main drawback is its Tc that is low as compared to that of HTS oxides. As a consequence, the cooling costs are assumed to be much higher, although cryo-coolers able to provide a high cooling power at 20K are now available [4]. Bulk MgB2 presents, however, advantages that could offset this inconvenient. Magnesium and Boron are abundant and available worldwide and MgB2 is a light, low cost and high hardness material. The fabrication process of MgB2 bulks by Spark Plasma Sintering-SPS [5] is simpler, takes much less time and is much less expensive than the techniques used for the growth of YBCO or REBCO bulks [6]. In addition, MgB2 bulks can be made with a priori no limitation on their dimensions and shape.
The non-conventional SPS process is based on the combination of a high current and a mechanical high pressure applied directly to the powder material. This technique presents the advantage to provide dense materials in a few minutes while mastering their microstructure. A lot of works have been reported since the introduction of SPS in research laboratories, and many groups have tried to understand the densification mechanisms involved. After a brief history of the SPS technique, the characteristics of this process will be detailed and compared to those of the other sintering techniques.
The densification, and the functionnal properties of superconducting MgB2 cryo-magnets sintered by SPS will be discussed. Levitation forces up to 700 N at 20 K measured on a 120 mm diameter MgB2 disc will be reported. The effect of the thickness and the diameter of cylindrical superconductors on the levitation force and the condition for stability in superconducting magnetic levitation will be also analysed.
References
[1] G. G. Sotelo, D. H. N. Dias, E.S. Motta, F.Sass, et al., Physics Procedia 36 (2012) 943 – 947
[2] F N Werfel, U Floegel-Delor, R Rothfeld, T Riedel, et al., Supercond. Sci. Technol. 25 (2012) 014007
[3] Yukikazu Iwasa, Physica C 445–448 (2006) 1088–1094
[4] https://www.cryomech.com/products/
[5] J. G. Noudem, M. Aburras, P. Bernstein, X. Chaud, M. Muralidhar and M. Murakami, J. Appl. Phys. 116, 163916 (2014).
[6] X. Chaud, S. Meslin, J-G. Noudem, C. Harnois, et al., Journal of Crystal Growth 275 (2005) 855-860.