Electrical AC loss measurements in superconducting coils

Electromagnetic losses occur in superconducting wires when they are exposed to time-varying fields or currents. The total losses are the sum of the hysteresis component, the coupling currents in the resistive matrix, the self field effect... In order to separate these different contributions, an electrical measurement method has been developed. The self field effect signal is analysed in LTc multifilamentary superconducting wires. The influence of the current wave shape (sinusoidal, triangular) is shown, To compare the loss mechanisms in HTS, a high temperature superconducting Bi coil has been studied. As for LTc material, they seem to be governed by the self field effect, but the eddy currents are no longer negligible and may be predominant at high frequencies.