Development of superconducting DC machines using bulk YBCO

An investigation is being made into building superconducting machines using YBCO bulks as quasi-permanent magnets. To investigate the performance of the superconductors in motor applications a test rig has been built in which a moving or vibrating magnetic field can be applied to the superconductor. The test rig allows two-dimensional motion of a magnet relative to a superconductor, in order that two-dimensional vibration modes can be investigated. This allows more accurate simulation of the conditions in a motor, and allows values of the absolute forces between magnet and superconductor during the motion to be inferred. The vibration methods used in the paper are suitable for measuring long-term behaviour of the superconductor-magnet interaction, including long-term decay of the trapped field when exposed to oscillations. The shorter tests reported here measure force/torque characteristics, and the stable limits of operation. Beyond these limits, a superconductor will be de-magnetised, resulting in a sudden loss of torque and machine damage.