Theoretical analysis of time constant measurements of technical superconductors

Time constant measurements were performed with superconducting NbTi/Cu strands, as well as with copper samples in slab geometry. Decaying eddy currents in the samples were induced both by half-cycle sinusoidal magnetic field pulses and by exponentially decreasing external fields. The signal of a pick-up coil surrounding the sample was used for the determination of time constant. A theoretical analysis was performed using a slab model approach. The main result is that the pick-up voltage signal is a sum of an infinite number of exponentials, whose contribution to the total signal depends on the mode, in which eddy currents are induced. This is in agreement with the experimental results