Multi-physics Coupling Mechanism In High Field Magnets

In this dissertation, a detailed study of multi-physics coupling mechanism in high-field magnets is carried out. The dissertation is divided into two parts:Part1presents the multi-physics coupling mechanism in pulse magnet. The main conclusions are:In chapter2, we present a complete coupling model of the electromagnetic and heat diffusion of two-dimensional axisymmetric multi-stage pulse magnet of the discharge process, fully taking into account the thermal effect, the magneto-resistance effect and the eddy current effect. On this basis, the change rules of the resistance, the inductance, the magnetic field, the current density and the temperature of the single-stage, two-stage and three-stage pulse magnets are given. Influence of the closed conductive ring on the magnetic field is studied. Effect of the axial cooling gap to improve the cooling efficiency of the pulse magnet is studied.In chapter3, we present a complete2D axisymmetric static elastic-plastic mechanical analysis model of multi-stage pulse magnet based on small strain condition, fully taking into account the initial stress and initial strain, the axial loading by the end plates, the Lorentz force, the thermal stress and the Bauschinger effect of the elastic-plastic materials such as conductors. This model can calculate the entire loading history from fabrication to discharge process, as well as cyclic loading, and can predict the fatigue life of pulse magnet. A new failure criteria of pulse magnet is presented:the maximum equivalent plastic strain exceeding the limit plastic strain is used to estimate the failure of elastic-plastic materials such as conductors; the maximum von Mises stress exceeding the ultimate tensile strength is used to estimate the failure of the orthotropic elastic materials such as fiber reinforcement materials. Based on the model and the new failure criteria, the elastic-plastic mechanical behavior of single-stage, two-stage and three-stage coils is carried out by finite element method. The impact of the different stress-strain curve models, the dynamic response and the bauschinger effect on the failure of the single-stage coil is studied. The impact of the mutual inductance on the elastic plastic mechanical behavior of the multi-stage coils is also studied. In chapter4, the mechanism of the fabrication process and discharge process of the limit indicators of pulse magnet is studied, including the impact of the prestress applied during coil winding, the axial loading by the end plates, and the discharge process of training on the failure and the plastic deformation of the irreversible inductance of the pulse magnet.Part2presents the multi-physics coupling mechanism in superconducting magnet. The main conclusions are:In chapter5, we present an electromagnetic design optimization model of the high temperature superconducting magnet based on different optimization algorithms. The optimization performance between SQP and GA is compared based on a high temperature superconducting magnet made by Bi-2223/Ag.In chapter6, we present a numerical analytical model of quench propagation of superconducting magnet, fully taking into account AC loss, Joule heat loss, convective heat transfer and external disturbances. On this basis, the quench analysis of a low temperature superconducting magnet is performed by finite element method.