| Within the support of Key Project of the National Thirteenth-Five Year Research Program of China,a prototype of China Fusion Engineering Test Reactor(CFETR)Toroidal Field(TF)coil has been designed and will be constructed before 2025.During the operation of the superconducting coil in the fusion device,the temperature evolution inside the magnet can’t be obtained,and only the inlet and outlet helium temperature can be monitored.In order to ensure the safe operation of magnets,thermal hydraulic analysis is an important part for the design and safe operation of magnets.This dissertation firstly analyzes and simulates the thermal behavior of CFETR TF coil during normal and off-normal operating conditions.Firstly,based on the nuclear heat load of the TF coil,the cooling design of TF coil is completed,and the position of inlet and outlet of helium,the number of cooling channels and the length of cooling channels are given.After that.the one-dimensional(1D)thermal analysis code,named GANDALF,was expanded by combining the SATIOKPF code.At the same time,the heat load of the coil case simulated by Fluent software and the three-dimensional(3D)magnetic field distribution of the TF coil calculated by Maxwell software were coupled,so that the expanded GANDALF program can complete the quasi-3D thermal-hydraulic analysis of the TF coil.Based on the extended GANDALF code,the influence of nuclear heat load on the temperature rise and temperature margin of TF winding is evaluated.In order to evaluate the reliability of the extended GANDALF code,the relevant simulation results is compared with the Italian 4C code,which has been verified by a series of experiments.the minimum temperature margin(ΔTmar min)calculated by the two code is only 0.07 K with the same input parameters and nuclear heat load,which verifies the reliability of the extended GANDALF code and provides the accuracy of thermal-hydraulic analysis of TF coils.During the normal operation of TF coil,its current remains constant,but the ramp rate of CS and PF coils will produce lots of AC losses in the TF coil.Therefore,the influence of AC loss on the winding temperature rise is simulated on the basis of the nuclear heatload,the two-scale distribution of AC loss of superconducting magnet in time and space during plasma discharge is given by using the extended GANDALF code,and the temperature distribution.hot spot temperature and temperature margin of superconducting coil during plasma discharge are given.The results show that the AC loss during normal operation will further reduce ΔTmar min of winding by 0.15 K.In the dissertation,the thermal-hydraulic analysis of TF coil under off-normal operation is also carried out,including quench,fast discharge and plasma disruption.In order to study the quench behavior of CFETR TF coils,the assumed quench initiation zones at the highest and lowest magnetic field positions of TF coils were analyzed,and the effect of quench detection threshold on hot spot temperature was investigated.It is found that 0.5 V quench detection voltage leads to hotspot temperature above 250 K in the low-field region.In order to meet the design criteria of the hot spot temperature,the quench detection voltage should be less than 0.2 V.For the fast discharge analysis,the eddy current loss of the coil case during the fast discharge is given.The analysis results show that the heat load of the coil case increases the winding temperature by 87.0 K.Because the current in the TF winding will decay to zero in a short time during the discharge,the coil is safe even if the winding temperature is very high.Based on the model established in the fast discharge analysis,the influence of the eddy current loss of the coil case on the temperature rise of winding during the plasma disruption is further analyzed.The results show that the temperature margin of the initial stage of plasma operation is smaller due to the rapid change of the current of CS and PF coils during the plasma ramp up stage,so the thermal load during the plasma disruption does not further reduce the ΔTmar min of the winding.In order to give the cool-down strategy of TF coil.the TF coil is also modelled by the 4C code,and the model of winding,casing,and the coupling model between the winding and the coil are carefully verified,and the influence of the cool-down rate,the pressure difference of winding and casing cooling channel,and the stop time during the cool-down on the maximum temperature difference of winding and casing are analyzed,and the cool-down strategy of TF coil is given.The relevant research results of this dissertation provide a certain basis for the design and safe operation of the TF coil cooling system,have important guiding value for the design and construction of superconducting magnets,and promote the development of magnetic confinement fusion in China. |
