Iterative homogenisation of trapped field in a bulk HTS solenoid with PFM

Abstract

Abstract Bulk high-temperature superconductors (HTSs) are capable of generating very strong magnetic fields while maintaining a compact form factor. Solenoids constructed using stacks of ring-shaped bulk HTSs have been demonstrated to be suitable for low-resolution nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI). However, these stacks were magnetised via field cooling, which typically requires a secondary superconducting charging magnet capable of sustaining a high magnetic field for a long period. A more economical alternative to field cooling is pulsed-field magnetisation (PFM), which can be carried out with an electromagnet wound from a normal conductor, such as copper. In this work, we present an additional advantage of PFM, where the trapped field in a stack of ring-shaped bulk HTSs is iteratively homogenised by manipulating the spatial profile of the applied pulsed field. Compared to field cooling with a uniform applied field, the variation in field along the central 10~mm of the solenoid is halved using this technique. If PFM of HTS rings could be advanced further to trap higher fields, this technique could be instrumental in magnetising HTS solenoids for NMR/MRI applications.