Developments of multifilamentary (MF) superconducting compound wires have gained much interest for their high transition temperature Tc, upper critical field Hc2, critical current density Jc and good stability. In these few years, A-15 crystal-type compounds Nb3Sn and V3Ga have been fabricated into MF wires for practical use by the so-called composite process. In this process, a composite of the Cu-Sn alloy matrix and Nb cores or that of the Cu-Ga alloy matrix and V cores is fabricated into a thin wire and then heat treated. The MF Nb3Sn and V3Ga wires show the highest over-all Jc, in the present available superconductors, for the field range from 50 to 120kOe and from 120 to 170kOe, respectively. In the pulsed current excitation, critical current of the MF V3Ga coil does not decrease up to exciting speeds of over 200kOe/sec while that of the MF Nb-Ti wire coil decreases rapidly at an exciting speed of about 20kOe/sec. The MF Nb3Sn conductors with large current-carrying capacities for nuclear fusion magnet are being developed. Besides A-15 crystal type compound, C-15 type Laves phase compound V2(Hf, Zr) have been also fabricated into a MF wire by the composite process in which a composite of the V sheath and Hf-66%Zr alloy cores is fabricated and then heat treated. This material shows nearly the same H-Jc characteristics as Nb3Sn and has much better mechanical properties than A-15 crystal-type compounds. The MF compound wires shall be widely used for winding homogeneous and stable high-field magnets which are useful for NMR research and, in larger scale, for synchrotron accelerator, fusion reactor, energy storage and electrical rotating machines.
