Impact of strain and field ramp functional form on thermomagnetic instabilities in composite Nb3Sn wires with multi-filaments inside the superconducting coil

We theoretically analyze the effects of Cu/SC (superconductor) ratio, strain, and the ramp path on thermomagnetic instabilities of the superconducting coil. By considering the multi-filamentary structures, we find that a lower Cu/SC ratio leads to higher temperature peaks. The strain causes a higher frequency of flux jumps and higher voltage peaks. The temperatures recover to working temperature more difficultly and SC wires quench earlier in the presence of strain. For the jagged ramp cases, few flux jumps occur at the decreasing branch, whereas frequent flux jumps can be observed promptly when the applied current exceeds the pre-existing peak. Our simulated results agree well with experimental observations in Nb3Sn coils. Additionally, unlike the pulsed flux jumps observed in linear ramp cases, giant and prolonged flux jumps are observed at the increasing branch with a sinusoidal ramp path when the applied current is sufficiently large.
Comment: 17 pages, 9 figures