New method of improving the stability of superconductors against flux jumping

Abstract

The threshold magnetic field for flux jumping in a bulk irreversible type‐II superconductor is known to be independent of its bulk critical current density. The present analysis shows that the flux jump field should be enhanced in a laminated superconductor in which the surface layer has a lower critical current density than the underlayer. For very large critical current density ratios, the limiting enhancement is 41%; for a 1:4 ratio the improvement is 32%. Experiments on laminated samples of Nb–48 wt% Ti alloys demonstrate an improvement in stability which is in good agreement with the theory. The technique may be useful in increasing the overload current rating of an ac superconducting power cable.