A.C. losses in some commercial superconductors

The a.c. losses in a variety of commercial superconductors at 4.2K have been measured in the frequency range 50¿400Hz. Transport current and transverse magnetic field were applied separately or in phase. The loss mechanism is shown to be hysteretic. Equations are derived for each test condition, and these correlate well with the tests over the entire range of measurements, provided that a critical current is chosen to fit the curves. This current is sometimes several times the measured critical current, suggesting that the latter is limited by instabilities. An analysis of the loss in the matrix of a filamentary round wire is included, and this is shown to correlate well with measurements.