Study on Magnetic Flux Dissipation and Field-Trapping Performance of HTS Bulk-Shaped Magnesium Diboride in Pulse-Field Magnetizing Processes

The magnetic flux dissipation from the MgB
₂
bulk magnets during pulsed field magnetization (PFM) processes has been estimated for the samples fabricated by hot-pressing (HP) and spark plasma sintering (SPS). We defined the parameters as field penetration ratio B
_P
/B
_a
and the field trapping ratio B
_T
/B
_P
to evaluate the flux motion and performance. The data plots of trapping ratio B
_T
/B
_P
showed us two regions which originate from the fast flux flow and flux jump. The field trapping performance was drastically degraded when the flux jump happened. Flux jump happened at various times after the peak field. A very late flux jump happened at 420 ms which severely degraded the trapped field. This time delay, much larger than the heat propagation time in the MgB
₂
sample, remains to be explained.