Magnetization Studies of High Jc Nb3Sn Strands

Magnetization measurements have been made on several high Jc Nb3Sn strands fabricated by different internal-Sn designs. In general these conductors have high magnetization at low fields, often exhibiting flux-jumps that are characteristic of large superconductor diameter. The effective filament size deff is approximately the size of the sub-element because the filament pack within each sub-element is fully coupled. Dividing the filament pack of the sub-element by adding Ta is effective for reducing deff and magnetization instability. But, some residual coupling across the dividers seems to remain below 6 K, perhaps due to Ta3Sn. Implications for accelerator magnets are discussed.