Influence of bending strain on transverse-field losses in NbTi multifilamentary superconducting wires with Cu matrix

To clarify the influence of the bending strain on transverse-field losses in NbTi multifilamentary superconducting wires with Cu matrix, we experimentally investigated AC loss characteristics of solenoidal sample coils with various curvatures. The total AC loss including the hysteresis loss and the coupling loss of sample coils was measured by the pickup coil method in an alternating transverse magnetic field with an amplitude of 1 T at 4.2 K in the frequency range between 0.01 Hz and 1 Hz. After the measured total loss was separated into the hysteresis loss and the coupling loss, each loss characteristics was studied. Measured data showed that the hysteresis loss was almost unchanged when the bending strain of the sample wire was within about 5%. On the other hand, the coupling loss decreased with an increase of the bending strain and the percentage of the decrease was about 15% when the bending strain was 5%. From the results of the conductivity measurement of Cu matrix, the decrease of coupling current loss due to the bending strain was quantitatively explained by the degradation of the conductivity of Cu matrix. In addition, the comparison between the experimental and theoretical results of the coupling time constant was discussed.