Low Temperature Fatigue Performance Analysis And Experimental Study Of Large Superconducting Magnet Helium Cooling Tube

As an indispensable component in the polar field system of large superconducting magnet,helium cooling tube mainly plays the role of inputting supercritical helium into the conductor coil and maintaining its operating temperature of 4.2K.During the operation of the magnet device,the helium cooling tube will undergo 30,000 cycles of electromagnetic loading.Whether the helium cooling pipe with irregular welds can operate smoothly under this working condition will determine the reliability of the entire polar field magnet system,and the fatigue failure caused by it will lead to the magnet system no longer maintain the low working temperature,and then causing the "quench" accident.Therefore,a series of theoretical analyses and experimental studies are carried out on the fatigue life of the designed helium cooling tube at low temperature.Firstly,according to the design requirements of CFETR helium cooling tube,the main material of helium cooling tube is selected and its preliminary structure model is designed.On this basis,four optimization schemes are proposed by slightly modifying the size of the connection between the helium cooling tube and the conductor.Secondly,a simplified finite element analysis model of the helium cooling tube was established,and the method combining theoretical calculation and simulation analysis was used to analyze whether the structural strength of the helium cooling pipe under the four schemes met the requirements,and the optimal design scheme was selected,which provided theoretical support for the fatigue life prediction of helium cooling pipe.Thirdly,the finite element analysis results were imported into the fatigue analysis module as a pre-processing file,and then the appropriate solution engine was selected,the material attribute parameters of 316 LN were input and the fatigue analysis software was used to fit the rough S-N curve,the load parameters of the magnet system were input and the corresponding constant amplitude load spectrum was generated,and finally the fatigue simulation analysis was completed.The analysis results show that the helium cooling tube broke after 34,270 load cycles,which is well within the design requirement of 30,000 cycles for the CFETR helium cooling tube.Finally,a racewayshaped hole groove is designed on the surface of the PF5 conductor and connected to the helium cooling tube through full penetration argon arc welding to complete the production of a full-scale test sample of the helium cooling tube.The test platform was built,the temperature compensated strain gauges were installed and the test load measured by the tensile machine was preloaded to complete the low temperature fatigue test of the helium cooling tube.The test results still show that the designed helium cooling tube meets the design requirements.In this paper,the fatigue analysis module of n Code is applied to the fatigue life prediction of helium cooling pipe for the first time,and the fatigue life of the designed helium cooling pipe can meet the design requirements effectively by combining the software simulation with the experimental study.This paper provides some reference value for evaluating the fatigue performance of similar components in fusion devices at low temperature in the future.