Detecting quench in HTS magnets with LTS wires -- a theoretical and numerical analysis

TL;DR

This paper presents a theoretical and numerical study on using LTS wires, like NbTi and Nb3Sn, as effective quench detectors in HTS magnets, emphasizing the importance of critical current temperature dependence over NZPV.

Contribution

It demonstrates that the temperature dependence of critical current, not NZPV, makes LTS wires suitable for quench detection in HTS magnets, supported by simulations.

Findings

LTS wires detect quenches effectively due to critical current temperature dependence.

Low matrix fraction or high matrix resistivity improves LTS detector performance.

Nb3Sn is a promising quench detector up to 20 T fields.

Abstract

Protecting a high temperature superconducting (HTS) magnet from a quench event is a challenging task. Because of the slow normal zone propagation velocity, the long reliable quench detection method by directly monitoring coil voltage may not be timely for HTS anymore, leaving HTS magnets under danger of overheating. Using a NbTi low temperature superconducting (LTS) wire to detect quench in coils wound with ReBCO HTS tapes have recently been experimentally proved, yet a theoretical study is still needed to further develop this technique and make it prepared to be applied more generally in high field magnets. In this manuscript, we have demonstrated that it is the significant difference in the temperature dependence of critical current between LTS and HTS but not the normal zone propagation velocity (NZPV), that makes LTSs good quench detectors. Simulations show that LTS quench detectors should have low matrix fraction or high matrix resistivity. At last, at field up to 15 T or 20 T, Nb3Sn is proven to be a good quench detector.