Suppression of Flux Jumps in High-$J_{c}$ Nb$_{3}$Sn Conductors by Ferromagnetic Layer

Flux jumps observed in high-$J_{c}$ Nb$_{3}$Sn conductors are urgent problems to construct high field superconducting magnets. The low-field instabilities usually reduce the current-carrying capability and thus cause the premature quench of Nb$_{3}$Sn coils at low magnetic field. In this article, we explore suppressing the flux jumps by ferromagnetic (FM) layer. First, we experimentally and theoretically investigate the flux jumps of Nb$_{3}$Sn/FM hybrid wires exposed to a magnetic field loop with constant sweeping rate. Comparing with bare Nb$_{3}$Sn and Nb$_{3}$Sn/Cu (Nb$_{3}$Sn wire wound by copper layer) wires, we reveal two underlying mechanisms. For lower field-ramping rate, the thermal effect of the FM layer primarily suppresses flux jumps. However, for higher field-ramping rate, both thermal and electromagnetic effects play a crucial role to suppress the flux jumps. Furthermore, we explore the flux jumps of Nb$_{3}$Sn/FM hybrid wires exposed to ac magnetic fields with amplitude $B_{a0}$ and frequency $\omega$. We build up the phase diagrams of flux jumps in the plane $\omega$-$B_{a0}$ for bare Nb$_{3}$Sn wire, Nb$_{3}$Sn/Cu wire, and Nb$_{3}$Sn/FM wire, respectively. We find that the region of flux jumps of Nb$_{3}$Sn/FM wire is much smaller than the other two wires, which indicates that the Nb$_{3}$Sn/FM wire has significant advantage over merely increasing the heat capacity. The findings shed light on suppression of the flux jumps by utilizing FM materials, which is useful for developing new type of high-$J_{c}$ Nb$_{3}$Sn conductors.