Study Of Heat Treatment Process Of CFETR CSMC Nb₃Sn Coil

Chinese fusion engineering testing reactor(CFETR),is tokamak magnetic confinement fusion device.The CFETR is for solving the energy crisis by controllable nuclear fusion,a new energy sources.The central solenoid(CS)coil is the key coil in the superconducting magnet of CFETR.The highest field of the CS coil is required to reach 12t,thus the two coils are winding by Nb3Sn superconductor.It because of the Nb3Sn coil can form a higher critical magnetic field than NbTi.The Nb3Sn produced superconductivity by heat treatment and the heat treatment can eliminate the residual stress in the process of winding.Therefore the study of heat treatment process of Nb3Sn superconducting coil is of great significance.Based on the general heat treatment scheme of Nb3Sn wire and the difference between CICC coil and wire,a new method of atmosphere protection for large CICC coil is proposed.The heat treatment process of CFETR CSMC Nb3Sn coil is completed,and the technical requirements of each process step are perfected.Based on the process and technical requirements of the heat treatment process,a set of heat treatment system and equipment is designed to verify the feasibility and scientificity of the process.According to the coil size and heat treatment requirements,the parameters of the heat treatment system and equipment are calculated,the design model of the equipment is determined.Finally the heat treatment system is built.Completed the system debugging of CFETR CSMC Nb3Sn coil heat treatment,and its main purpose is to verify whether the heat treatment system can meet the requirements.The purpose of debugging include:verifying the power and accuracy of the heating system meet the requirements;verifying the temperature uniformity on the same size sample coil meets the requirements;verifying the argon protection can protects the super conductor,it is not oxidized;verifying the short sample coil can meet the final assembly requirements when it used the coil fixture.After the debugging of heat treatment system and the experimental results of heat treatment process meet the requirements,the heat treatment of model coil is started.Analyzed the input parameters of power and researched the precise control of furnace temperature.In the two model coil experiments,heating was carried out under the two states of fan on and off,and the temperature curve and temperature uniformity of each area on the coil were analyzed during heat treatment process.The results show that the temperature in the furnace can be precisely controlled by adjusting the input parameters of the heating power and the fan is on or off.Analyzed the composition of the superconducting sample surface and the impurities in the Argon gas,the scientific and reliability of argon protection is evaluated.Measured the critical current and n value of superconducting strand samples,the reliability of the heating system is verified.Measured the coil contour,the feasibility of coil fixed scheme is evaluated,and heat treatment process is the great role in the manufacturing process of Nb3Sn coil.According to the evaluation results of the model coil test,adjusted the heat treatment process,perfected the input parameters of the heat treatment system,and achieve the conditions of the real coil heat treatment process.Completed the preliminary experimental verification process,formulate detailed Nb3Sn coil heat treatment process specification,carry out real coil heat treatment.Heat treatment is carried out in strict accordance with the process specification.In the process of heat treatment,parameters are input according to the technical requirements in the specification.After the completion of heat treatment,the feedback parameters are compared with the requirements to evaluate whether the results of real Nb3Sn coil heat treatment process meet the expectations.