Disc-Assisted Pulsed-Field Magnetisation of HTS Rings

Solenoids constructed by assembling ring-shaped bulk high-temperature superconductors (HTSs) have been demonstrated to be capable of trapping a sufficiently strong and uniform magnetic field for nuclear magnetic resonance and magnetic resonance imaging. These systems, however, were magnetised using field cooling, requiring a large and expensive secondary superconducting magnet to generate the external field. Pulsed-field magnetisation (PFM), on the other hand, is a much more economical and practical method to magnetise bulk HTSs, as it can be carried out using a normal conductor (such as copper) to generate a brief pulsed magnetic field. The trapped field following PFM is found to be significantly lower than that achieved with field-cooling. This is due to the large quantity of heat generated within the bulk during the rapid change in the applied field. While this heating effect has been exploited to improve the pulse magnetisation efficiency of disc-shaped bulks, it has proven detrimental when magnetising ring-shaped bulks. Here, we present a refinement of the PFM procedure of ring-shaped bulks that can assist with increasing the trapped field. By inserting bulk HTS discs into the bore of a ring and pulse magnetising the discs before the rings, and subsequently removing the discs, we show that a higher field can be trapped in the ring.