Effects of a Diffusion barrier on the AC Losses of a Bronze-Processed Nb₃Sn Multifilamentary Superconducting Wire

3. Shape of the Saturated Region and Coupling Losses

Abstract

Effects of a tin-diffusion barrier on the coupling current loss was investigated for a bronze-processed Nb₃Sn multifilamentary composite, and a general expression for the coupling current loss was derived for the composite with several normal-conductor jackets subjected to a transverse magnetic field with a trapezoidal wave form of a practical sweep rate.
In a low frequency range, the present expression is reduced to the one presented previously by authors et al., where the ratio of the coupling current loss between the cases of a Nb and a Ta barrier is equal to the ratio between the effective coupling time constants τ_eff's for the corresponding cases. It was shown that the saturation tendency of the increment of the coupling current loss with the increase of the sweep rate begins at remarkably small value of the sweep rate within the practically used range, especially for the case of composite with the tin-diffusion barrier made of Nb. The present theoretical results were compared with our observed data for both cases of Nb and Ta barriers, and the agreement between them seems to be fairly satisfactory.