Stability Analysis Of High-Current High-temperature Superconducting Composite Conductor In Fusion Device

High-current superconducting composite conductor have been widely used in many fields such as energy,power,transportation,and medical treatment.Stability against a series of interference factors is closely related to the safety and reliable operation for superconducting cables.Thus qualitative analysis and quantitative calculation for the stability of superconducting composite conductor are of great significance.The thesis focuses on research and application of stability analysis methods for high-current superconducting composite conductors.First of all,using the stability analysis methods for Low-Temperature Superconductor(LTS)Cable-In-Conduit-Conductor(CICC),one-dimensional finite element model of the high field region winding of the longitudinal field magnet of the China Fusion Engineering Experimental Reactor(CFETR)is built.The operating characteristics of high-performance Nb3Sn CICC conductors is analyzed,and the stability margin and parameter variation of the conductor under typical electromagnetic and mechanical perturbations are calculated.The temperature margin is higher than 2.0K under estimated operating conditions,and the energy margin under the most unfavorable condition is 11.41mJ/cc.Meanwhile,the parameters of high-performance Nb3Sn CICC conductors after recovery and quench are calculated under the two typical thermal perturbation conditions.Summary and application of LTS stability analysis method lays a good foundation for the stability analysis of High-Temperature Superconducting(HTS)composite conductors.An improved high-stability ReBCO HTS composite conductor is presented,based on the 2-generation HTS coated conductor as well as recent design of HTS composite conductor.The improvements and sub-cable structure are the focus of the presentation.Aiming at the structure of improved conductor,the key mathematical models related to the stability are discussed,including the normalized critical current density model of ReBCO conductor with flux pinning force correction,the simplified equivalent electrical circuit model and the heat transfer model.The stability of the improved ReBCO composite conductor is calculated and analyzed from three aspects:AC loss,stability margin and quench behavior,using 1-demension finite element method as well as stability analysis method mentioned above.By building a simplified 2D electromagnetic model,the magnetic field permeability and normalized current distribution of the composite conductor under alternating current are analyzed.Outer tapes away from the axis bear most of the operating current,and has the largest AC losses.The influence of perturbation,thermal contact resistance,operating current and background magnetic field on stability margin of the ReBCO composite conductor were discussed separately.Quench behavior under typical electromagnetic perturbation as well as mechanical perturbation are simulated,and a number of suggestions are given to improve the stability and safety of high-current ReBCO composite conductor,from the perspectives of temperature distribution,hot spot temperature,helium parameters,and quench detect&protect.