Magnetic lens effect using Gd-Ba-Cu-O bulk superconductor in very high magnetic field

We investigate the performance of a magnetic lens in very high magnetic fields exceeding 24 T. The magnetic lens is composed of Gd-Ba-Cu-O superconducting bulk materials. The unique configuration of the magnetic field amplifier, which consists of slits and electrical insulation in the bulk, allows the magnetic flux density to be further enhanced by a background magnet. In field cooling operation, the external magnetic field was varied ∼4 T from 24.2 to 28.3 T and a total magnetic flux density of 30.35 T was found at the center of the device with a background magnet. The magnetic lens additionally increased the magnetic flux density by 2.05 T due to the lens effect. However, it was also observed that the bulk was partially quenched when the external field was varied. This partial quench and recovery of the bulk magnet is considered to be one factor that limits the performance of the lens effect. Finally, we are able to generate a substantial magnetic flux density of 2 T under very high magnetic field because we can obtain such high-field without further electrical power.