Almost all superconducting alloy materials with practical value are niob-based alloys, mainly including niob-zirconium (Nb -- zr), niob-titanium (Nb -- Ti) and niob-zirconium -- Ti (Nb -- Z -- Ti). The composition range (%) is Nb -- (25 -- 35) zr, Nb -- (45 -- 55)Ti and Nb -- 42Zr -- 10Ti, Tc is 11 -- 11.5k, 9 -- 9.5k and 10.3k, respectively. Hc2 at 4.2k temperature is 8 -- 9.5t, 11.5 -- 12.5t and 10.5t, respectively. Jc under 4.2k5t was 1000A/mm2, 3800A/mm2 and 2800A/mm2, among which nb-ti still had Jc value of 1600A/mm2 under the high magnetic field of 8T.
Niobium titanium single core wire production process is mature, and began to develop multi-core wire. Some progress has also been made in multielement alloys based on nb-ti and nb-zr. The Hc2 of nb-ti-ta, nb-ti-ta-zr and nb-ti-ta -- Hf are all higher than that of the best nb-ti binary alloy, but the Hc2 is not improved much at 4.2k, only 0.3t, and only at a lower temperature can Hc2 be significantly improved. For example, the Hc2 of nb-43ti-25ta at 2K is 15.5t, 1.3t higher than that of the best nb-ti alloy. This superconducting material will be used in the experimental model of 12T nuclear fusion. Nb -- 42Zr -- 6Ti's Jc is not low, but it cannot be made into multi-core wire. Jc of Nb -- 40Zr -- 10Ta under 4.2k and 5T is 2000A/mm2.
Strong magnetic field superconducting material is the first class Ⅱ superconductors, between Hc1 and Hc2 containing magnetic flux line, when a current flows through a conductor lorentz force who can lead to magnetic flux line movement and resistance. In order to improve current carrying capacity, magnetic flux lines are usually anchored by increasing dislocation density, grain boundary and second phase particles. The friction heat generated by mechanical disturbance, the sudden change of magnetic field or current, will cause the flux jump and cause local heat, which is the instability of superconducting materials. In order to prevent the loss of overshoot due to the flux jump, stabilization measures should be taken for the conductor, such as freezing stability, adiabatic stability and dynamic stability. Superconductors are usually made by burying them in oxygen-free copper (200-300) with a high residual resistance ratio. Copper quickly transfers the heat generated by the flux jump to liquid helium, returning the conductor to zero resistance. In order to prevent the adjacent coupling effect between cores, some high-purity copper is replaced by copper-nickel alloy or copper-manganese alloy. Copper-nickel alloy has the effect of resistance scattering, while manganese has the effect of spin reversal scattering.
