Study on the Remagnetization Process to Improve the Field Homogeneity of the Stacked HTS Bulk Magnets

The compact NMR magnets consisting of stacked HTS bulk annuli trapped by a field cooling (FC) method have been developed. However, it is difficult to trap a uniform magnetic field above 4.7 T (200 MHz-class NMR magnet) and field homogeneity under 0.01 ppm/cm³ at liquid nitrogen temperature (77.4 K) because of the low mmb Jc-mmb B characteristics of present HTS bulk magnets. On the other hand, the strength and homogeneity of the magnetic field required for the NMR relaxometry device are 1.5 T and 150 ppm/cm³ respectively; these values are much lower than the conventional NMR device. It is relatively easy to generate a magnetic field over 1.5 T at 77.4 K using the stacked HTS bulk annuli, but it is still hard to obtain 150 ppm/cm³ field homogeneity with the conventional superconducting magnet (SCM) as the magnetizing magnets. In this paper, we proposed that the homogeneity had been improved by utilizing the remagnetization process.