Effects of additives on the superconducting properties of powder‐metallurgically produced Cu‐Nb3Sn composite wires

Cu‐Nb3Sn microcomposite wires with additions of In, Ga, and Ge to the bronze and of Ta to the niobium have been produced by the hot‐powder‐metallurgical preparation method. The characteristic influences of the additives on the superconducting properties are discussed on the basis of measurements of critical current densities (up to fields of 19–22 T), critical temperatures as well as x‐ray microprobe analyses. Although all alloying additions are incorporated into the Nb3Sn filaments, significant enhancements of the upper critical field by 2 and 4 T, respectively, can only be achieved for Ta and Ga. With an appropriate choice of the preparation parameters the current‐carrying capability is considerably improved in the field range above 12 T. The optimized current densities reach values of 108 and 2×107 A/m2 at 16 and 19 T, respectively.