Detecting Quench in HTS Magnets With LTS Wires—A Theoretical and Numerical Analysis

Using a co-wound and insulated NbTi low temperature superconducting (LTS) wire to detect quench in coils wound with high temperature superconducting (HTS) tapes has 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 accelerator magnets. In this manuscript, we present some theoretical and numerical analyses, which confirm a few important facts: 1) 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; 2) LTS quench detectors should have low matrix fraction or high matrix resistivity to increase its normal resistivity and therefore enhance its ability as a quench detector; 3) Heat transfer between cable and detector is important, but a poor heat transfer condition is tolerable; 4) At field beyond 15 T, Nb
₃
Sn, Nb
₃
Al and MgB
₂
all show good potential as quench detectors, and some degradation in wire performance is also acceptable.