HTS Bulk Pole-Field Magnets Motor With a Multiple Rotor Cooled by Liquid Nitrogen

High-T_c superconductor (HTS) rotating machine with melt-textured Gd-123 bulk pole-field magnets was assembled and tested. The axial gap type motor with neither brush/slip ring nor iron core was composed of a kind of multiple rotor, i.e., a twinned rotor. On each rotor disk, there are eight Gd-123 HTS bulk magnets. The bulk magnets were cooled down with circulating liquid nitrogen supplied inside the rotors. Separately, triple-layered armature copper coils cooled with liquid nitrogen were fixed for pulsed current magnetization for the bulks. Rotation of the twinned rotor provide a better single-phase waveform in 200 rpm compared to in single rotor operation. Magnetic flux density and its distribution on each bulk are stable with averaged decay of 4% for seven hours continuous synchronous operation. The results give a poof on the realization of strong flux collection motor.