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Description
A superconducting bulk magnet can generate a strong magnetic field in a compact and lightweight device. Among magnetization methods for bulk magnets, pulsed-field magnetization (PFM) is effective for industrial applications because a bulk can be excited on-site in a short time. In terms of the generated magnetic field, it is reported that almost 100% of the sample's field trapping performance can be achieved at 77 K. However, when using at temperatures as low as 30 K, it is only about 50%. Then, to improve the trapped field, advanced PFM methods such as changing the magnetizing device to extend the pulse width, changing the pulse waveform, and applying a pulsed field multiple times with varying the temperature and the amplitude of the applied field have been reported.
In this paper, we propose a new PFM technique with the addition of First Applying a Very Small magnetic field immediately before the application of a pulse magnetic field of the desired magnitude (hereinafter called "FAVS" method). Applying a low magnetic field causes a small amount of heat to be generated in areas with low properties, which reduces the superconducting properties of those areas and weakens the magnetic shield, resulting in those areas becoming a path for the magnetic flux. By subsequently applying a magnetic field of the desired magnitude, the magnetic flux can be expected to efficiently penetrate through the pathway and be trapped inside the sample. The proposed method has the advantage of great versatility because it takes advantage of slight differences in the properties of any sample.
To confirm the effectiveness of the proposed method, PFM experiments were conducted using a φ60 mm × 20 mm GdBCO bulk. The temperature was set to 20 and 30 K, and a magnetic field of 5.0 or 5.4 T was applied immediately after the first application of 0.8-3.0 T. The trapped field distribution on the pole surface was measured after magnetization, and the total magnetic flux was calculated from the measured data. As a result, it was confirmed that applying a magnetic field of about 0.8 to 1.5 T for the first time improves the total magnetic flux compared to applying a single pulsed field of 5.0 and 5.4 T, demonstrating the effectiveness of the proposed FAVS method.
