Levitation Characteristics of a Fully Superconducting Magnetic Bearing

In this study we tested a fully superconducting magnetic bearing. According to a previously published design, the bearing was completely made from high-temperature superconducting (HTS) coated conductors comprising a stack of active stator coils and passive rotor coils. The stator is powered by a superconducting dynamo. In a 77 K bath, this setup was able to create a levitation force of 32 N in zero-field cooling mode. During the dynamo standstill that followed the charging, the excitation of the active coils and the levitation force decayed because of normal conducting joints between the in series connected active stator coils. The bearing was discharged via the dynamo after the standstill phase. After a full discharge the bearing still exhibits levitation as well as radial forces, indicating that the passive rotor was magnetized by the active coil during the charging loop. This is also supported by a clear hysteresis occurring in the levitation force during charge and discharge. Interestingly, the remanent levitation force requires that both components change their function: the formerly passive coil now acts as a superconducting permanent magnet, whereas the previously active coil is discharged, free of transport current, and creates induced currents that generate levitation force in interaction with the rotor's magnetic field.