Pulsed field magnetization of a bulk HTS with a coil sharing the same cryocooler
Résumé
Bulk High-Temperature Superconductors (HTS) have been studied extensively in order to act as “permanent magnet” with magnetization largely above conventional rare earth compounds. Recently, a field of 17.6 T has been achieved inside a stack of two GdBCO samples of diameter 25 mm [1]. However, significant technical challenges of bulk superconductors remain in cooling and magnetization technologies for practical applications. Pulsed field magnetization (PFM), which is a traditional method for activating permanent magnets, is considered as the most practical technique to magnetize bulk HTS in superconducting applications. A trapped field of 5.2 T in a bulk superconductor has been reported by Fujishiro et al. [2]. This record value has been achieved by means of an iron core placed above and below the bulk, and using a coil outside the cryostat with dimensions largely greater than the sample.
In this paper, we will discuss on the benefit of studying in situ magnetization, with pulsed magnetic fields generated by a small coil sharing the same cryostat than the sample. With this setup, the bulk HTS is attached and cooled down using the second stage of a Sumitomo 204S cryocooler while the magnetizing coil is cooled down with the first stage. Experiments are ongoing in order to improve the test rig. Several key results will be presented such as cooling time, maximal applied field, and trapped fields at several temperatures of a YBCO pellet with a 12 mm height and a diameter of 35 mm. The failed tests and some numerical simulations will complement the obtained results in order to explain the key features of such a system.
References
[1] J. H. Durrell, et al., Supercond. Sci. Technol. 27 (8), 082001 (2014).
[2] H. Fujishiro, et al., Physica C 445, 334-338 (2006).