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

TL;DR

This study models how strain, ramp path, and material ratios affect thermomagnetic instabilities in Nb3Sn superconducting wires, revealing critical factors influencing flux jumps and quenching behavior.

Contribution

It provides a theoretical analysis of the impact of ramp form, strain, and material composition on flux jumps in multi-filament Nb3Sn wires, aligning with experimental data.

Findings

Lower Cu/SC ratio increases temperature peaks.

Strain leads to more frequent flux jumps and earlier quenching.

Sinusoidal ramp causes prolonged flux jumps at increasing current.

Abstract

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.