Magnetic instability of superconducting wire in the changing magnetic field

Abstract

Existing theories are not suited for explaining the stability of superconductors in a rapidly fluctuating magnetic field. Therefore, an attempt was made to study the stability of superconductors in such a magnetic field. Special attention is given to magnetic diffusion in the flux creep condition and dependence of the flux jumping on the fluctuation of magnetic field is explained. It has been proposed in the past that the maximum magnetic field first flux jump which a superconductor can shield without flux jumping is proportional to 1/3 to 1/2 power of the speed of magnetic field increase. The relation between the rate of field increase and the flux jump formation field was determined. Using a single strand Nb-48% Ti wire, the effect of copper ratio, the presence or absence of insulating varnish, copper foil, and the magnetic field sweep rate on the initiation of flux jumps was studied.