The Study On The Fabrication And Property Of Superconducting Joint For The Second Generation High Temperature Superconducting REBCO Tapes

Based on the high temperature superconductor REBa₂Cu₃O_7-x(referred to,RE=Y,Sm,Gd and other rare earth elements),the second generation high temperature superconducting possess both the excellent basic physical properties of REBCO superconductors and the biaxial texture advantages of coated conductors.Due to this fact,the outstanding superconducting properties of REBCO tapes are exhibited in the liquid nitrogen temperature,which including high critical current density and irreversible field,excellent mechanical strength etc.Therefore,the REBCO tapes are more promising than the first generation high temperature superconducting tapes in the field of superconducting high current applications.In order to solve the problem of length limitation for the preparation of superconducting tapes in practical applications and realize the persistent current operation mode of the REBCO superconducting magnet especially,the superconducting joint of REBCO tapes is paid extensive attention and research.The specific content of this thesis focuses on the physical and chemical process exploration of the realization of the second-generation high temperature superconducting coated conductor superconducting joint.The systematic research has been carried out from the aspects of process exploration,preparation and physical properties of superconducting joint.The main work of the paper is as follows:Aiming at the requirements for the preparation of superconducting joints of the second-generation high temperature superconducting REBa₂Cu₃O_7-x(REBCO)tapes,the eliminating process of the metal stabilizer of REBCO tapes was systematically studied.Developed a cheap and fast chemical method to etch the metal Cu/Ag stabilizer of Y_0.5Gd_0.5Ba₂Cu₃O_7-x tapes,and deeply studied the chemical reaction mechanism of the etching process and the specific reason of the Ic attenuation of the YGd BCO tapes.The structure of the superconducting layer and the superconducting properties of the YGd BCO tapes etched by this method are hardly affected,which lays a solid foundation for the subsequent preparation of superconducting joints.Laser drilling technology is an effective method to provide oxygen diffusion channels for the superconducting joint of tapes.In this paper,the effect of microholes processed on the surface of YGd BCO tapes on its own superconducting performance was systematically studied.The systemic electromagnetic performance measurement and the finite element simulation methods were used to study the influence of the microholes array structure(the diameter of microholes,distribution distance and density)on the superconducting performance(I_c,T_c,maximum diamagnetic signal,I_c anisotropy under low field)and AC loss of the YGd BCO tapes.It was found that the optimized microholes structure can improve the magnetic flux pinning characteristics of the YGd BCO tapes under low field and have a significant impact on the AC loss of the YGd BCO tapes.In the research of preparing the superconducting joint of YGd BCO tapes by the fusion atom diffusion technology,the superconducting performance of the joints was optimized by using pure oxygen atmosphere,and the superconducting joint of YGd BCO tapes were successfully prepared.It was found that the surface roughness of the superconducting layer was one of the key factors affecting the surface microstructure and supercurrent transport characteristics of the superconducting joint.The dominant theoretical explanations and related models was proposed that the supercurrent transport characteristics at the superconducting joint are mainly caused by the superconducting weak connection characteristics.The molecular dynamics simulation was used to simulate the atomic diffusion behavior at joint region,and the results were consistent with experimental results.A novel method for preparing the superconducting joints of YGd BCO tapes was explored which called“liquid-phase-assisted sintering and texture fusion”technology.Unlike the fusion atom diffusion technology,this new technology uses the liquid phase generated by the melted YGd BCO to improve the bonding strength at the joint interface,and then form a textured interface by recrystallizing and growing these liquid phases.Therefore,this technology has the characteristics of insensitivity to the surface roughness of YGd BCO layer.Preliminary research shows that the new technology can be used to prepare the superconducting joints of YGd BCO tapes with superconducting properties,and has demonstrated great optimization potential.