Superconducting technology has been significantly improved since the superconductor Y-Ba-Cu-O was discovered. This technology has been applied to many medical image-processing applications such as magnetoencephalogram (MEG) and magnetic resonance imaging (MRI). Because the superconducting phenomenon occurs at extremely low temperatures, liquid helium or liquid hydrogen is essential to obtain a low-temperature environment. In addition, it is well known that the decompression of the liquid helium creates superfluid helium. This phenomenon improves the performance of the superconducting devices. For that reason, a vacuum pump, which can be used at a cryostat, is required. In this paper, we propose a motor that has a small size and simple structure for use in the cryostat. The proposed motor consists of an axial self-bearing motor, superconducting magnetic bearings, and permanent-magnet repulsive-type passive magnetic bearings. The design of the motor and control method is introduced. The experimental results show that the proposed motor has a high possibility for high-speed rotation at extremely low temperatures.
