Hot Spot Temperature in an HTS Coil: Simulations With MIITs and Finite Element Method

E. Haro, A. Stenvall, J. van Nugteren, G. Kirby
2015 IEEE transactions on applied superconductivity  
MIITs, a zero-dimensional concept to study hot spot temperature, has been previously used to estimate hot spot temperatures and quench heater delays in NbTi and Nb3Sn magnets. However, quench behaviour is completely different in high temperature superconducting (HTS) magnets due to the slow normal zone propagation velocity and high temperature margin. Because MIITs concept does not take into account thermal diffusion in the magnet, opposite to the finite element method (FEM) analysis, the
more » ... ence of these concepts is studied in this paper. Here we have taken the approach to compute the hot spot temperatures for a future HTS magnet, designed to be built from REBCO Roebel cable, with MIITs and FEM simulations. The magnet protection is accomplished with a dump resistor, and the effect of quench detection threshold voltage on the hot spot temperature has been studied. Furthermore, the inductance of the magnet increases with the magnet length. Thus, there exists a maximum inductance of the magnet which should not be exceeded to be able to protect the magnet only with a dump resistor. The hot spot temperatures with different values of inductance are also studied in this paper. Our simulations show, that the hot spot temperatures computed with MIITs are from 60 K to 150 K higher than those of FEM analysis. Thus, MIITs concept seems unreliable when considering hot spot temperatures in HTS magnets protected with only dump resistors. However, MIITs concept might be a usable tool when comparing different magnet designs. If 400 K is the upper limit for the hot spot temperature and the protection scheme includes only a dump resistor, the length of the investigated magnet can be increased to only such value that the magnet inductance is at most 50 mH.
doi:10.1109/tasc.2015.2396945 fatcat:jo6uojjcpjf5hjsj7v2gjvdkum