Performance Study Of High Temperature Superconducting Coil Based On Ice Impregnation

The second generation high temperature superconducting(HTS)materials have the advantages of high current-carrying capacity,high critical magnetic field and high mechanical strength.In recent years,with the rapid development of HTS material production process and HTS magnet technology,HTS materials have been more and more widely used in high field magnets.Due to operating in a strong magnetic field environment,high field superconducting magnets will be subjected to huge Lorentz force during operation.Epoxy resin impregnation is usually required to improve its mechanical strength.However,a large number of studies have found that epoxy impregnation will cause the degradation of the critical current of HTS magnets,which seriously affects the life of the magnet and the engineering application of the HTS tape.Scholars have proposed methods such as paraffin impregnation,heat shrink tubing,and no-insulation coils to solve the problem of critical current degradation.However,these methods also have problems such as complex processes,high costs,and charging delays.Therefore,to find a suitable impregnation process is one of the key technologies of HTS magnets.This paper applied the ice impregnation technique of pulsed magnets to HTS coils for the first time.The research on critical current,thermal stability,mechanical strength and electrical insulation strength provided a reference and technical support for the future application of ice impregnation technology in superconducting magnets.This paper has carried out in-depth research work around exploring the new impregnation process of HTS magnets.The main innovations of this paper are as follows:(1)In this paper,the concept of ice-impregnation HTS coil is put forward for the first time and verified by experiments.The experimental results showed that ice impregnation technology would not cause the degradation of the critical current of superconducting coils after multiple thermal cycles;and then according to the simulation of the thermal stress during the cooling process and the experimental study on the adhesion of ice to the surface of the HTS tape,the degradation mechanism of the critical current of the superconducting tape was explored.(2)Based on the ice impregnation process of HTS coils,this paper also conducted an experimental study on the thermal stability of ice impregnation superconducting coils.The experimental results of the hot spot thermal disturbance showed that the minimum quench energy(MQE)of ice impregnation superconducting coils was about 3 times that of epoxy impregnation coils.The experimental results of pulse overcurrent showed that the pulse overcurrent time of the ice impregnation superconducting coil was about 10 times that of the epoxy impregnation coil.According to the experimental results,the ice impregnation coil has better thermal stability than the epoxy impregnation coil,which is of great significance to reduce the hot spot temperature of quench zone.(3)In the research process of ice impregnation superconducting coils,it was found that ice was prone to crack at 77 K and the mechanical strength of ice was low.In order to optimize the ice impregnation process,this paper proposed ice mixture process and freezing under pre-pressure process.These two methods could solve the cracking problem and also effectively improve the mechanical strength of ice,increasing the compressive strength of ice by 16 times and the tensile strength by 3 times.(4)In order to verify the application of ice impregnation process in superconducting magnets,combined with a 12 T background magnet,this paper designed an 8 T HTS insert coil by using genetic optimization algorithm.Considering the influence of screen current and interlayer separation,the electromagnetic analysis and stress analysis of HTS coil were carried out.Based on the research results,the outermost reinforcement of glass fiber cloth and ice was proposed.The structure design of HTS coil and sample rod was preliminarily determined.