Fully superconducting magnetic bearing made of seamless superconducting coils

• Applicant: Dr.-Ing. Tilo Espenhahn
• Subject Area: Mechanics ; Engineering Design, Machine Elements, Product Development
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 452135712

Superconducting magnetic bearings are characterized by contactless and therefore wear-free operation, which is a decisive advantage over conventional mechanical bearings. It enables more efficient and therefore more economic operation, which is suitable for applications such as flywheels, superconducting wind generators or high-speed motors. Usually, superconducting magnetic bearings combine permanent magnets with superconducting bulks. A stable levitation is achieved by fixing an inhomogeneous magnetic field inside the superconductor, which is usually cooled with liquid nitrogen. A characteristic feature of such superconducting bearings is the ability to create restoring forces in all spatial directions. Therefore, a rotating superconducting bearing is stable in axial and radial direction under tensile or compressive load. In the first phase of the project, a completely superconducting bearing was realized from superconducting coated conductor material only. However, the coils used in this bearing contain normal conducting soldered joints generating ohmic losses, which need to be compensated by additional cooling. In addition, the coils need to be recharged periodically to maintain a stable magnetic field. The aim of the new proposal is to implement seamless coils in the fully superconducting bearing of the first project phase replacing the lossy soldered coils. The required new coils need to be manufactured by a special cutting and winding technique, which was tested in small scale in the first project period. This technology makes special demands on the commercial coated conductors and required an additional coating. Therefore, atomic layer deposition will be tested to deposit a stable protecting layers on the complex geometry of the coil, which will secure a long-term stability of the fully superconducting coils. The bearing properties of the fully superconducting bearing with coated seamless coils will be studied afterwards. This includes static and dynamic measurement of the bearing stiffness and damping. The low-temperature cryostat developed in the first phase of the project enables such investigations down to a temperatures of 20 K. At the end, the bearings from both project phases will be compared regarding their functional properties, required cooling power, and operation time of the coil charging system. The results will enable an evaluation of the efficiency increase by using seamless coils in fully superconducting bearings. Additionally, a small demonstrator will be realized to show the principle of operation for such a bearing to the broader public.

• DFG Programme: Research Grants