Air force applications of lightweight superconducting machinery

The U.S. Air Force has actively developed superconductor technology since 1961. Early Air Force involvement was disappointing due to the primitive technological state of superconductivity in the mid- 1960´s. Following the successful application of stability theories, programs in the areas of superconducting alternators, magnetohydrodynamic (MHD) generator coils and inductive energy storage coils have been productive. The universal Air Force requirement for lightweight machinery eliminates cryostatic stability from consideration for lightweight designs of superconducting coils. Maximum overall current density is necessary. Serious transient field losses are induced by armature currents in synchronous alternators, conductive gas currents in MHD generators and discharge currents in energy storage coils. Shock and vibration structural support of the superconductor to prevent motion induced quenches remains a challenge to the machine designer. Exotic superalloy or advanced composite structures are required to achieve high stiffness and lightweight. Development of flexible multifilament Nb3Sn is underway to create thermal margin for superconducting machinery. The problems of achieving ultra-lightweight performance are reviewed with special emphasis on the interrelated problems of potting, structural support and cooling at high current density in an environment of transient magnetic field. Second generation machinery development programs are beginning. With acceptance of superconducting systems and attendant cryogenic support problems, wider application of superconducting machinery may result.