Improvement of the trapped field of REBCO bulk activated by pulsed field magnetization with a large soft-iron yoke

We study to increase the trapped magnetic field of a REBCO bulk magnet excited by pulsed field magnetization (PFM). In PFM, a soft-iron yoke is used to expose the bulk to the magnetic field for a long time. Although a small yoke 40 mm in diameter was used in our previous study, it was changed to a large yoke 64 mm in diameter in this paper. Accordingly, the pulse width was extended by 13%. When a GdBCO bulk 60 mm in diameter and 20 mm thick was magnetized by varying an amplitude of the applied field and temperature in a bulk magnet system using a two-stage GM-type refrigerator with a cooling capacity of 12 W at 20 K, the maximum trapped flux density reached 4.07 T on the center of the bulk surface and 2.56 T on the pole surface at 20 K. Moreover, the total magnetic flux was 3.28 mWb, which was about 13% larger than that of a small yoke. This result suggests that this method is useful in practice because the trapped field can be enhanced only by changing the soft-iron yoke.