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To investigate the electrical properties of the joint between superconducting multifilamentary wires, we applied a radio frequency superconducting quantum interference device (r.f.-SQUID) voltmeter to measure the extremely small voltage induced across the joint. We measured the time variation of both the current induced in a loop of superconducting wire and the voltage induced across the joint. A voltage sensitivity in the pico-volt range was obtained with this apparatus. Comparisons of currentdecay between superconducting loops with soldered, spot-welded and cold-welded joints were made. A flux creep-like phenomena was seen in the current-decay for the coldwelded and spot-welded joints.

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We are currently under development of a 1 MW-class HTS ship propulsion motor, for which rotating HTS coil made of Bi-2223 tape wire has already been successfully cooled down to 30 K and attained the target performance. There, the electric loss estimation in the HTS tape wire is required under practical operation conditions. The magnetic field angle dependency on I C -B characteristics of Bi-2223 used for the field winding was measured at 40 K. Furthermore, the interlinkage flux density on HTS coils in the horizontal and vertical directions were calculated using threedimensional magnetic field simulations. It was found that the estimated electric loss of the entire HTS coil using these measured and simulated results was about 9 W at the operating field current of 200 A, which was considerably small compared with 30 W at 215 A, and that the operating field current of 200 A was appropriate and desirable considering the required refrigerator capacity.