Measurements of current distribution in a 12-strand Nb3Sn cable-in-conduit conductor

Abstract

Experiments were performed to measure directly the current in each strand of a 12-strand Nb3Sn cable-in-conduit superconductor during current and/or external magnetic field ramps. The goal of the experiment was to get straightforward evidence of current maldistribution in a cable-in-conduit conductor (CICC). A heavily instrumented sample coil from Nb3Sn TPX-TF strands was specially prepared. Severe non-uniformity of the strand currents were found during field ramp. Immediately before a quench the individual strand currents within a triplet differed by as much as an order of magnitude. During field ramps with constant transport current, the currents in some strands were observed to drop rapidly and then recover. The data show that quench development in the CICC is a complicated phenomenon involving dynamic redistribution of current among the strands. Non-uniformity of current along the strands du ring quench was also observed. (C) 1997 Elsevier Science Ltd.