Gas properties studies using reflectometry : first steps towards real time cooling gas temperature monitoring in superconducting magnets

To carry out fast (real time) temperature monitoring of the coolant gas and thus to observe evolution and enable the prevention of the quenching in superconducting (SC) magnets the frequency and time domain reflectometry (FTDR) i.e., analysis of microwave electromagnetic signals propagating in coolant gas channels, have been recently proposed. Here the results of numerical and experimental studies of fundamentals of the application of the microwave (RF) FTDR for quench monitoring are discussed. Through the studies, we show that variations of external conditions induce change in the gas permittivity, which can be measured fast and accurately. The methodology presented is based on correlations between thermodynamic gas variables (temperature and pressure) with its electromagnetic properties (refractive index). The sensitivity to both temperature and pressure suggests that the technique allow monitoring other anomalies i.e., not only temperature, including the gas pressure, the flow rate variations and turbulence. Through the numerical studies it was found that a localised hotspot can be detected with minimal time delay, which is crucial consideration for quench prevention and magnet “health” monitoring. The experimental data observed agree well with the theoretical understandings, and the preliminary findings promote further investigations in cryogenic environment of the proposed technique.