Actively shielded high-field air-core superconducting machines

This paper describes an approach for obtaining very high power density in an electrical machine by significantly increasing the air-gap magnetic flux density and eliminating the ferromagnetic steel traditionally employed to carry and shield magnetic flux. A novel concept is used to address a key challenge with this topology, that of containing the magnetic fields within the machine. An arrangement of main coils and a set of compensating coils, inspired by actively shielded magnetic resonance imaging magnet designs, are employed to cancel out the field outside the machine without the use of iron while maintaining air-gap field levels that are three to five times greater than conventional machines. For an example 10-MW motor study, the outer diameter is reduced by 35%, with corresponding weight reduction, using only 17% more superconductors.