The study to improve the field homogeneity of the NMR relaxometry magnets using the packaged HTS bulks with various iron rings

The compact magnet for NMR device that consists of a stacked high temperature superconducting (HTS) Gd-Ba-Cu-O bulk annuli was trapped by a field cooling method. However, it was difficult to trap the 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 Jc-B characteristics of present HTS bulks. On the other hand, the strength and homogeneity of the magnetic field required for NMR relaxometry device are 1.5 T and 150 ppm/cm³ respectively. It is easily to generate the trapped magnetic field over 1.5 T at 77.4 K using the stacked HTS bulks, but it is still hard to obtain 150 ppm/cm³ field homogeneity with the conventional superconducting magnet (SCM) as the magnetizing magnets. Therefore, we have studied the compensation methods to improve the field homogeneity. In this paper, we proposed the packaged HTS bulk magnet consisted of HTS bulks annuli and various iron rings as the field compensation, and investigated it in analysis and experiment.