Losses in superconducting multifilamentary Roebel bars

The power losses of NbTi multifilamentary Roebel bars have been measured at T = 4.2 K for magnetic field conditions as expected in large turbogenerators. The measurements were carried out in the low frequency region both between 5.10^-3- 8.10^-2Hz using field amplitudes of 3 T or 6 T with triangular variation and up to 1.5 Hz for sinusoidal varying amplitudes ranging from 0.03 - 1 T. In each case, different bias fields were applied to the test coils wound from the cable conductor. The experimental results are compared with the common AC-loss theory which agrees generally very well to about 20%. The time constants and coefficients obtained from both calorimetric and electrical measurements are consistent within the two field variation modes.