We are developing a 7.5 kW-360 rpm synchronous motor with a superconducting rotor. The rotor is 6-pole type and has no iron core. The armature winding is wound with copper. The designed operating temperature is 40 K. It will be cooled by forced-flowed helium gas. We have finished the winding of the first superconducting field coil with YBCO superconducting tapes fabricated by IBAD-PLD method. It is a 62-layer solenoidal coil. The total length of YBCO tape is 400 m. The magnetic field in the field winding is about 0.4 T at maximum and that in the gap is 0.2 T. We cooled it down to 20 K by G-M type cryocooler and investigate the transport properties in advance of the winding of the other field coils. We verified the stable operation up to 100 A at 40 K against the rated current of 50 A. In addition we prepared the cryogenic rotor system and installed 6 pieces of dummy copper coils instead of superconducting coils. We cooled it down to 30 K by forced-flowing helium gas and tested it by rotating up to 360 rpm. We verified the satisfactory good mechanical and thermal operation.
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