Effects of Tantalum Addition on Hysteresis Losses and Critical Current Densities of Powder-Metallurgy Processed Nb3Sn Superconducting Wires

Powder-metallurgy processed (PMP) multifilamentary Nb3Sn superconducting wires have been fabricated. The critical current densities and hysteresis losses of the wires are measured and the effects of tantalum addition to niobium on them are investigated. Although tantalum addition decreases both the critical current densities and the hysteresis losses, the reduction of the hysteresis loss is more pronounced. As a result, the effective filament diameter is diminished. The critical current density of the PMP Nb3Sn wire may depend on the combination of the bridging among Nb3Sn filaments and the super-normal interface pinning centers. This wire includes 3721 composite cores which consist of copper and Nb3Sn. The non-homogeneous deformation of filaments is reduced by tantalum additions. Both the bridging among Nb3Sn filaments and the super-normal interface pinning center energies may be reduced by tantalum additions, and therefore depressing the critical current density. Tantalum additions also depress the sausage-like deformation of composite cores, suggesting that both bridging and coupling among the composite cores is suppressed. Consequently both the hysteresis loss and the effective filament diameter are decreased.