The superconducting material of niobium-titanium alloy whose core wire diameter is below 0.5μm. With the successful development of low-temperature superconducting materials, superconducting materials have begun large-scale application in industrial production, scientific research, medical and health aspects. Especially in recent years, the application of superconducting technology has not been limited to DC, such as synchrotrons, AC superconductors, superconducting colliders, transformers on controlled devices, superconducting cables and inductive energy storage, etc. all require AC superconducting materials . When the superconducting material is applied under AC, its AC loss is relatively large, and it must be reduced to an allowable level. With the continuous development of superconducting technology, the problem of AC loss is getting more and more attention. It has become another important feature of superconducting materials, like critical temperature, critical current, and critical magnetic field.
According to theoretical analysis, it is considered to increase the matrix resistance of the conductor, manufacture ultra-fine superconducting core wire (below 0.5 μm) and ultra-fine superconducting wire diameter (below 0.1 mm), and reduce the twisting pitch of the superconducting wire, etc. Method can reduce AC loss.
NbTi and Nb3Sn ultrafine core superconductors are good AC superconducting materials. In order to increase the strength of the conductor and transmit larger currents, this material should be twisted into a cable and a cooling channel of liquid helium should be provided on the cable. NbTi ultrafine core superconducting wire is a composite superconducting wire with CuNi as the matrix or Cu and CuNi as the mixed matrix, and NbTi as the superconducting core wire. The preparation process of the superconductor generally adopts the method of multiple combined extrusion and stretching, and can also adopt the method of multiple hydrostatic extrusion. The critical current density of the material under direct current is (0.95 ~ 3) × 105A / cm2 (5T, 4.2K). The AC loss value of the material is currently the main research indicator. Nb3Sn ultrafine core superconducting wires are mostly made by the bronze method or the inner tin method. They are first formed during application and then subjected to diffusion treatment.