Concentric Slitting of a Ring-Shaped Bulk Superconductor for a Reduction in Circumferential Inhomogeneity of the Trapped Magnetic Field

Magnetic field trapped in a superconducting bulk magnet has non-negligible inhomogeneity resulting from nonuniform superconducting properties. Counteracting the inhomogeneity is one of the challenging problems in applications of bulk magnets to NMR and MRI. In this study, we fabricated a bulk magnet with concentric slits for trapping a field with reduced circumferential inhomogeneity. A GdBaCuO superconductor, 60 mm in outer diameter, was sliced with a thickness of 2 mm. Three equally-spaced concentric slits were formed using a sandblasting technique. The magnets were cooled with liquid nitrogen in an external field of 600 mT. The z-component of trapped field was measured along circular trajectories. The magnet with slits exhibited smaller inhomogeneities of fields compared with an equal-sized one without slit. On a trajectory 30 mm in diameter, the field inhomogeneities of magnets with and without slits were 7% and 11%, respectively. On a 13-mm trajectory, the slits resulted in the reduction of inhomogeneity from 0.9% to 0.3%.