Homopolar motor with high temperature superconductor field windings

A superconducting field winding, assembled with discrete coils wound with bismuth 2223 high temperature superconducting (HTS) wire, has been successfully operated in an electric homopolar motor designed and built by the Naval Surface Warfare Center. The motor's field winding is composed of two HTS coils fabricated by American Superconductor Corporation and two HTS coils fabricated by Intermagnetics General Corporation. These field winding coils were produced for the Navy under contracts with the Naval Research Center. At a HTS field winding operating temperature of 4.2 K, the motor produced 125 kW (167 hp) of output power. At a temperature of 28 K the motor power developed was 91 kW (122 hp). In comparison to other motor types, a homopolar motor provides an ideal operating environment for a superconducting magnet. The design, construction, and operating characteristics of this machine are described. Information describing the HTS field winding and its superconducting capabilities is presented along with that for the laboratory test facility used to measure the performance of the machine. Motor measured performance results and those predicted by computer simulation are compared and presented. An assessment of the state of the engineering development of HTS superconductors for magnet applications and recommendations for future development are made.