Study On Electromagnetic And Mechanical Behaviors Of Superconducting Coil Based On The Self-consistent Model And The T-A Method

High temperature superconducting materials(HTS)have an excellent current-carrying capacity in high background magnetic field,which have been widely used in different fields such as medical,transportation,and energy.In engineering applications,the high temperature superconducting magnets are subjected to high electromagnetic force in extremely low temperature,high current,and strong magnetic field.The high electromagnetic forces can cause critical current degradation and even lead to damage of superconducting materials.To ensure the safety of superconducting devices in extremely complex environments,the mechanical behavior analysis of superconductor is of great significance.In this dissertation,the electromagnetic and mechanical characteristics of Bi-2212 and REBCO superconducting coils are calculated by the self-consistent model and the T-A method,respectively.The critical current degradation and the stress distribution characteristics of Bi-2212 and REBCO superconducting coils under high background magnetic field are analyzed.The main contents are as follows:Firstly,the numerical methods for simulating the electromagnetic field of superconductors are introduced in detail,mainly including the self-consistent model and the T-A method.The characteristics of the above two numerical models are compared with simple examples.The selfconsistent model has significant advantages in quickly estimating the critical current of superconductors,and the T-A method is more suitable for solving the transient problems.Secondly,a two-dimensional(2D)model of Bi-2212 strand wire structure based on the selfconsistent model is established.The magnetic field and critical current density distribution of a single wire are calculated.Through reasonable simplification,an equivalent model is established with high accuracy to reduce the computational cost.Then,two dimensional axisymmetric model is given to calculate the changes of critical current density and magnetic field distribution in the coil with electromechanical coupling.The effects of different parameters such as background magnetic field and the coil inner diameter on the critical current and circumferential stress of coil are compared.The results show that the strain has a significant effect on the critical current when the inner diameter of the coil is larger,the number of winding layers is larger or the background magnetic field is higher.Then,the critical current and magnetic field distribution of coils with two different winding modes are discussed.The optimization schemes to improve the electromagnetic and mechanical properties of the coils are given.Finally,the electromagnetic models of the REBCO coil are established based on the T-A method and the self-consistent model.The differences of critical current density,magnetic field distribution and Lorentz force distribution calculated by the two methods are compared.The results show that the self-consistent model can't take into account the shielding current effect because of the steady-state calculations.The T-A method is based on Maxwell's equation for transient calculation,the shielding current effect is considered and the results are more accurate.Then,a electromechanical coupling model is established to analyze the radial and circumferential stress distributions of the HTS magnet.Additionally,the difference of stress distribution of each component of REBCO superconducting tapes is discussed.