A Spoke-Supported Superconducting Rotor With Rotating Cryocooler

This article presents the design of a superconducting (SC) rotor with a spoke supported structure that minimizes the heat loss and enables the motor to be cooled by one cryocooler. The main challenge with the SC machines is the need to maintain the SC coils at cryogenic temperatures. Though usually placed in the vacuum, the cryogenic coils still receive a large amount of heat through the conduction of the torque tube which connects to the ambient temperature. The heat flown into the system exceeds the cooling capacity of a cryocooler and requires the boiling of cryogen, which comes with a more complicated and bulky hardware system. The SC rotor proposed in this article uses a spoke system to support the cryogenic windings. Connecting the windings to the shaft, the flexible spokes with low thermal conductivities transfer the torque from the windings to the shaft. The spoke system has much lower thermal conductivity than a traditional torque tube. Preliminary results show that with the ambient temperature 298 K and the cryogenic temperature at 40 K, the total heat transfer rate from the ambient environment to the cryogenic environment is less than 0.1 W, within the capability of a cryocooler that can be mounted on the rotor. The cryocooler is arranged concentrically with the shaft of the rotor. Thermal straps connecting the cold end of the cryocooler to the windings to conduct the heat. An analytical model is built for the rotor. The rotor's mechanical property and its thermal behavior are analyzed jointly so that the spoke system is optimized for high stress and lightweight. A physical model is also built to test the cryocooler performance in the rotational environment. A previous study shows that the sterling-cycle cryocooler performance has not deteriorated at 1800 rpm at the temperature of 100 K. The proposed design involves a lower operating temperature at 40 K and a high vacuum environment surrounding the cold head.