Abstract
Fast quench detection is a key requirement for the successful implementation of superconducting magnet technology. In high temperature superconductor magnets, this issue is especially challenging due to the low quench propagation velocity, and presently represents one of the main factors limiting their application. A new detection technique based on stray-capacitance monitoring is proposed. The capacitance between electrically-insulated magnet elements, such as magnet structure and end parts, is utilized as an indication of local heat deposition in the conductor. In fact, the relative permittivity of helium drops when it changes from the liquid to the gaseous phase. Thus, when heating occurs, part of the helium impregnating the insulation layers boils off, and the monitored stray-capacitance decreases. The proposed technique is successfully demonstrated on three small-scale Bi-2212 magnets manufactured at the Lawrence Berkeley National Laboratory. Results from the detection of thermal runaways and spot-heater induced quenches are reported and discussed. Advantages and limitations of the stray-capacitance method with respect to conventional quench detection methods are assessed.
Highlights
Detection of the quench development is critical for the protection of superconducting magnets
The highest electrical permittivity change occurs when the fluid is transferred from the liquid to the gaseous phase
The main mechanism causing the capacitance variation is the change of electrical permittivity of the cryogenic fluid impregnating the insulation layers
Summary
Detection of the quench development is critical for the protection of superconducting magnets. Fast quench detection in high-temperature superconductor (HTS) magnets is more challenging due to the very low normal zone propagation velocity [3,4,5] This feature is one of the factors currently limiting wider application of HTS magnets. Various alternative quench detection methods have been explored in the past These attempts include systems monitoring the voltage across coils magnetically coupled to the protected coil [6, 7], mechanical vibrations [8,9,10,11,12,13], local variations of magnetization and current distribution [14,15,16,17,18,19,20], variation of fiber refraction index with temperature [21,22,23,24,25,26,27], or voltage across non-contact capacitive sensors [28, 29]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
