Fundamental Evaluations of Applicability of LTS Quench Detectors to REBCO Pancake Coil

Quench detection in a rare-earth barium copper oxide (REBCO) coil is difficult due to the slow normal zone propagation in it. To address this issue, we have proposed a quench detection method using a low temperature superconducting (LTS) wire as a quench detector. A demonstration experiment in our previous research using a REBCO tape showed that the quench detector was able to detect quench in the tape before it burned out. Therefore, to verify the applicability of this method to a real magnet system, we first numerically evaluated the quench detectability of Nb-Ti and Nb₃Al detectors attached on stacked REBCO tapes at 4.2 K under magnetic fields up to 20 T assuming the coil excitation process. The results indicated that the detectors were not needed to be placed in each layer of the REBCO coil. Furthermore, we have conducted an experiment using a REBCO single pancake coil with the Nb-Ti quench detector at 4.2 K and self-field. As the results of the experiment, we demonstrated that one Nb-Ti detector was able to detect the quench in the REBCO coil even if there were at least three REBCO tapes and the polyimide tapes between the detector and the hot-spot in the REBCO coil.