Suitable Shape and Arrangement of HTS Bulk and Permanent Magnet for Improving Levitation Force in a Magnetic Levitation Type Superconducting Seismic Isolation Device

We have investigated levitation force characteristics of a magnetic levitation type superconducting seismic isolation device composed of HTS bulks and permanent magnets. Large levitation force at a small gap of less than 3 mm has been already obtained, while only small levitation force at a large gap of more than 5 mm. In a practical use of the superconducting device, the HTS bulks should be cooled by not LN₂ but a cryocooler. This means that large levitation force at a large gap of more than 5 mm is required due to a vacuum layer thickness in a cryostat. Therefore, we investigated the suitable size and arrangement method of the permanent magnet and the HTS bulk to improve the levitation force at a large gap of more than 5 mm effectively. By adopting a permanent magnet arrangement of "Halbach array", we could greatly improve the levitation force at a large gap of more than 5 mm. Based on the experimental and computed results of levitation force and magnetic field distribution, we could achieve further improvement of the levitation force by optimizing the size of the permanent magnet and the HTS bulk. The suitable width and thickness of the permanent magnet were 10 mm against a disk-shaped HTS bulk 32 mm in diameter and the suitable thickness of the HTS bulk was less than 2 mm at a gap of more than 5 mm.