Fast time-varying current triggering flux jumps of multi-filamentary Nb3Sn wire exposed to oblique magnetic field

Abstract

Due to the oblique magnetic field and rapid time-varying current, the electromagnetic response and thermomagnetic instabilities of high-field superconducting dipole magnets are quite different from the solenoid coils. In this work, we theoretically investigate the flux jump of composite multi-filamentary Nb3Sn wire with high critical current density exposed to an oblique magnetic field and fast transport current. The thermomagnetic stability/instability regions are obtained with respect to flux creep factor and oblique ratios of magnetic field. It is found that the parallel component of the oblique magnetic field can suppress the flux jump. Unlike slow current, it is interesting to find that the fast variations of self-field by high ramp current can trigger flux jumps in Nb3Sn wire. The fast current triggering flux jumps can be tuned by the static oblique magnetic field. Furthermore, we demonstrate that current-like distribution is more likely to trigger quenches, while the magnetic field-like distribution is more likely to trigger flux jumps. The findings of this work are helpful for the optimization of the superconducting coils exposed to oblique magnetic field and fast time-varying current.