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Description
We have developed a new fast quench detection method for superconducting devices utilizing the REBCO superconductor tape itself as a microwave transmission line. Unlike voltage detection where the signal is proportional to the length of the normal zone, a 100-m-long transmission line will effectively become two 50-m transmission lines if quench occurs midway along the tape, joined by a resistive transmission segment. The standing waves formed in the transmission line are immediately disturbed, which can be readily sensed by a frequency analyzer in sweep mode that acts as a source of excitation and a sensing circuit. We have experimentally verified that the resonance peaks in both reflection (s11) and transmission modes (s12) change immediately and drastically on quench, and the resonance peaks are sensitive to size of quenched region. Quench detection has been demonstrated with simultaneous transport current through bare tape (13% critical current (Ic)), tape with silver overlayer (39% Ic), and with copper stabilizer (58% Ic). Quench triggered by a heat pulse was quickly detected in all cases by a shift in the amplitude and frequency of s11 reflection. The efficacy of the quench detection method in the presence of transport current has been confirmed in multi-turn coils constructed with epoxy and paper insulation. This quench detection method is a potent approach for HTS magnets, without a need to co-wind extrinsic sensors.
This work was supported by Office of Naval Research award N00014-21-1-2429.
