Enhanced proximity effect coupling due to the presence of a Nb barrier in fine NbTi multifilamentary composites

Recent measurements have shown that hydro-extruded fine-filament multifilamentary NbTi/Cu composite (MF) strands in which the NbTi filaments were not protected by Nb barriers exhibited extremely low proximity effect (PE) coupling. To examine this anomaly two series of MF strands were fabricated, one with and the other without the Nb barrier. Magnetization measurements performed on these strands confirmed that the presence of the Nb barrier was associated with an enhancement of the PE coupling. It is concluded that any additions to the matrix of a MF strand that would provide the needed protection against Cu/NbTi interface compound formation, without requiring the use of Nb as a barrier, can be expected to lower the tendency for PE coupling