Levitation Force Characteristics of High-Temperature Superconducting Bulks in a High Magnetic Field
The levitation force of high temperature superconducting (HTS) bulks can be enhanced by raising the strength of the external magnetic field. As to the field of HTS magnetic levitation (maglev), many researchers have also obtained this conclusion by levitation experiments above a permanent magnet guideway (PMG). However, the experimental results have limitations because the magnetic field above the PMG is relatively low, around 0.4 T at the 15 mm working height. In order to obtain more comprehensive levitation force characteristics of HTS bulks, it is necessary to carry out more experiments in high magnetic field. In this paper, the effects of magnetization angle and external field gradient on the levitation force of an HTS YBCO bulk which was manufactured with a top-seeded multi-seeded melt-textured process were studied. We set up a levitation force measurement system based on a 5-T Cryogen-Free Magnet (CRY-CFM-5 T-300-H3, Cryogenic Limited). The HTS bulk was cooled by liquid nitrogen in zero-field-cooling condition, and the external magnetic field was enhanced from 0 to 3 T. The HTS bulk was rotated 30° each time and finally rotated to 90°. Experiments show that the levitation force decreases from θ = 0° to 90°, where θ is the angle between the upper surface of the HTS bulk and the horizontal plane. The conclusion that the levitation force increases with the increase of the external magnetic field gradient in high magnetic field was also further confirmed.