Tunable superconducting magnetic levitation with self-stability

Abstract Magnetic levitation based on the flux pinning nature of type II superconductors has the unique merit of self-stability, making it appealing for applications such as high speed bearings, maglev trains, space generators, etc. However, such levitation systems physically rely on the irreversible magnetization of the superconductor, which makes the levitation status nonadjustable after establishment. Moreover, practical type II superconductors in levitation systems inevitably suffer from various sources of energy losses, leading to continuous levitation force decay. These intrinsic drawbacks make superconducting maglevs inflexible and difficult for long term operation. Here, we propose and demonstrate a new form of superconducting maglev which is reversibly tunable and with self-stability. The maglev system uses a closed-loop type II superconducting coil to lock the flux of a magnet, establishing self-stable levitation between these two objects. A flux pump is used to modulate the total magnetic flux of the coil without breaking its superconductivity, thus flexibly tuning the levitation force and height while maintaining self-stability. For the first time, we experimentally demonstrate a self-stable type II superconducting maglev system which is able to counteract long term levitation force decay, adjust levitation force and equilibrium position without ancillary electromagnet, and establish levitation under zero field cooling condition without the need of counteracting repulsive electromagnetic forces. These breakthroughs may facilitate practical applications of type II superconducting maglevs.