A detailed experimental investigation on the E-J characteristics of NbTi filaments and comparison with theoretical models

The transition from a completely lossless regime to the normal state of a high current density superconductor is not sharp and it can be well described by a power law. On the other hand the behaviour of a weakly pinned, highly homogeneous material is rather different, the voltage being a linear function of the current above a threshold value, and zero below. Several authors have attempted to explain this difference; this problem is quite involved since the full multifilamentary structure and the presence of the matrix must be taken into account. We shall briefly outline a few of the models proposed, which we later investigate experimentally, trying to disentangle the effect of the structure from the intrinsic superconductor behaviour. This has been accomplished by comparing the E(J) curves of both full wires and their extracted superconductor filaments