Quench Detection Utilizing Stray Capacitances

Fast detection of the occurrence of a quench in a high-field superconducting magnet is required in order to avoid damage due to overheating of the coil's spot when the quench initiated. This problem is particularly challenging for high temperature superconductor (HTS) magnets due to the low normal zone propagation velocity. As a result, quench detection is one of the factors presently limiting the application of HTS coils. Here, a method based on the measurement of the variation of the stray capacitances between the magnet's elements is proposed. Upon quench initiation, the capacitances between the elements and the coil vary due to multiple effects, including cryogenic fluid boil-off, variation of the dielectric properties of the insulation material, and thermal expansion, which locally changes the distance between coil and metal parts. Results from the first application of this method on a small-scale HTS coil are reported and discussed. Advantages and limitations of this technique with respect to state of the art quench detection methods are discussed.