Abstract
Bulk superconductors can act as trapped-field magnets with the potential to be used for many applications such as portable medical magnet systems and rotating machines. Maximising the trapped field, particularly for practical magnetisation techniques such as pulsed field magnetisation (PFM), still remains a challenge. PFM is a dynamic process in which the magnetic field is driven into a superconducting bulk over milliseconds. This flux motion causes heating and a complex interplay between the magnetic and thermal properties. In this work, the local flux density during PFM in a MgB2 bulk superconductor has been studied. We find that improving the cooling architecture increases the flux trapping capabilities and alters the flux motion during PFM. These improvements lead to the largest trapped field (0.95 T) for a single MgB2 bulk sample magnetised by a solenoidal pulsed field magnet. The findings illustrate the fundamental role bulk cooling plays during PFM.
Highlights
Trapped-field magnets utilise vortex flux pinning in type-II superconductors to generate large static fields which persist until warming
We present a brief introduction on how remanent magnetisation affects the flux motion behaviour building on existing numerical studies in bulk pulsed field magnetisation (PFM) [18]
Through a combination of multi-pulsing and improved cooling architecture, a trapped field of 0.95 T was achieved at 20 K—which we believe is the largest reported PFM value for a single MgB2 bulk using a solenoid coil
Summary
Trapped-field magnets utilise vortex flux pinning in type-II superconductors to generate large static fields which persist until warming. Multi-pulse techniques, which have been shown to produce higher trapped fields in REBCO PFM [17], have yet to be systematically conducted in a single bulk MgB2 sample. BJ has been theoretically predicted in various models utilising a range of assumptions [4,5,6,7,8] These models have indicated several parameters which may influence BJ including: critical current density, external cooling capabilities, pulsing temperature, and magnetic field ramp rate. These factors can be vastly different between materials and experimental set-ups making simple comparisons between studies difficult. The interplay between these different types of flux motion is still poorly understood in PFM
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