A. c. losses of superconducting solenoidal coils are measured by calorimetric method under applying uniform a. c. magnetic field or flowing through a. c. current to them. The circular cross-sectional wires, which have five sorts of copper ratio over a range from 2.1 to 8.3, are composed of twisted 271 filaments of Nb-Ti-Zr 50μ in diameter embedded in a matrix of low resistivity copper. The range of applied a. c. currents is 0-15 rmsA and magnetic field 0-200 Oe, at 50Hz.
In these conditions, the observed a. c. losses result from eddy current losses due to “proximity effect” and are proportional to the square of magnetic field or current. The a. c. losses in the fine multifilamentary superconducting wires decrease in about 1/4 of those in the pure copper wires with the same diameter as them. The losses of solenoidal coils can be calculated by introducing a mean magnetic field in the winding and a numerical constant to the eddy current loss formula, whether both ends of coils are open or close and the magnetic field is an applied field or self field.