Research And Related Experiments Of Quench Detection Technology For High-Temperature Superconducting Magnet

High-temperature superconducting(HTS)materials have the advantage of high critical characteristics,which is the best choice for high-field magnets,therefore HTS materials are used in CFETR CS coils.The research on quench detection technology is the key issue in the development of new magnets and is the premise of the safe operation of magnet systems.On the basis of the research on the HTS quench propagation mechanism,this study explores new a quench detection technology because the traditional technology cannot meet the safety detection of an HTS magnet.At the same time,the multi-scale structure quench propagation models from tape and cable to magnet were established during the early stage of HTS magnet development.The relevant quench detection platforms for superconducting tape were designed,and many experiments were carried out to confirm and analyse new technologies and models.Combined with the new quench detection technology,a quench detection system for the HTS magnet was proposed to provide scientific evidence for the safe operation of large HTS magnets in the future.The main contents and innovations of this thesis are summarised as follows.On the basis of the research on quench mechanism,the analysis of quench propagation characteristic parameters for HTS magnets was conducted.Compared with the traditional quench characteristics of low-temperature superconducting(LTS)materials,the difficulties and importance of the quench detection technology of HTS magnets were highlighted.The first domestic distributed optical fibre sensing technology(DOFS),which is based on optical frequency domain reflectance(OFDR),is developed to detect the quench of the HTS magnet using the coherent characteristics of Rayleigh scattering signals.The real-time adjustable spatial resolution on the mm level is realised.Using low-temperature experiments,the first Chinese calibration curve of distributed fibre at ultra-low temperature(4.2 K)was obtained.This thesis proposes a new algorithm,which is based on the length of minimal normal zone(Lmpz).The feasibility of this technology for HTS quench detection was analysed in detail.On the basis of the OFDR technology,the technology verification experiments on the current HTS lead sample,HTS tape double-pancake coil,and the quench propagation experiment on the CORC structure cable were systematically performed.Compared with the traditional quench detection method(VTs),the new approach has clear advantages.Specifically,the development boundary and hot spot location of the normal zone can be accurately captured;a change in the hot spot characteristics can be detected in advance,and the distributed measurement of quench space continuity can be realised.In addition,electromagnetic noise can be completely avoided.DOFS realised an embedded optical fibre wiring,which can deal with the complex magnet structure.The optical fibre structure can be directly implanted into the magnet insulation material,which confirms that the new detection technology can be used for quench detection,which is essential for HTS magnets.For the first time in China,the three-dimensional multi-physical field-coupled dynamic quench model of the ReBCO CORC structure cable has been developed.The influence of joint resistance on the shunting characteristics between tapes and the quench characteristics under different thermal pulses were analysed in detail.After performing a sample experiment to verify the reliability of the model,a theoretical analysis model to investigate the quench detection technology of the CORC structure for HTS magnet was developed.A lot of work was performed on the application of HTS cable to fusion magnets in the future,and an effective method was developed for the subsequent performance evaluation and safe operation of HTS cable.At the same time,the temperature-controlled superconducting coil quenching experiment platform was independently designed and built to carry out a thermal analysis model.On the basis of the experimental platform,a three-dimensional quenching model of the ReBCO double-pancake coil was established,and the internal sample coils of the platform were simulated and analysed.The steady-state coupled field analysis and quenching characteristics of the non-insulated ReBCO double-pancake coil under heat pulse were realised.Finally,on the basis of the mature experience of LTS quench detection combined with the new quench detection technology and analysis of the quench model,the main quench detection and auxiliary detection parallel method were used to propose the design of the quench detection system for HTS magnet.