Speaker
Description
The results of numerical and experimental studies of fundamentals of the quench monitoring technique based on frequency and time domain reflectometry (FTDR) are discussed. To carry out fast (real time) monitoring of the coolant gas temperature and thus to observe evolution and prevent the quenching in superconducting (SC) magnets the techniques of detection and analysis of microwave electromagnetic signals propagating in coolant gas channels have been recently proposed. The techniques should also allow monitoring other anomalies including the gas pressure and flow variations. Through the studies, we show that variations of external conditions (affecting gas temperature and pressure) induce change in the gas permittivity, which can be measured fast and accurately. We demonstrate that: (a) monitoring and analysing the spectral lines shifts (in a range of a frequencies) allow the average changes of the gas properties observation within the whole system; (b) measuring variations of a single frequency signal amplitude and phase, propagating in the cooling pipes, allowing evaluation of the gas local temperature fluctuations i.e. hotspots appearance.
The methodology presented is based on the established correlations between thermodynamic gas variables such as temperature and pressure with its electromagnetic properties i.e. refractive index. Through the numerical studies it was found that a localised hotspot can be detected with minimal time delay, which is crucial consideration for the systems necessitating rapid response for quench prevention and magnet “health” monitoring i.e. cooling pipe integrity, fast temperature fluctuations of the gas and etc. The experimental data observed agree well with the theoretical understandings, and the findings demonstrate the validity of the proposed technique. While the technique holds significant potential for monitoring HTS magnets it also offers a possibility to develop new monitors in the areas encompassing many devices using SC magnets including fusion reactors, MRI systems and others.
