Quantitative Study On Several Electric-magnetic-mechanical Basic Characteristics In Superconducting Materials And Their Electromagnetic Structures

The studies of the electromagnetic and mechanical characteristics on superconductors are the critical topics to develop the superconducting applications. Figuring out the electromagnetic field distributions and their evolutions, AC losses and mechanical behaviors in superconducting structures makes us understand deeply their properties and guarantees the safety and stability for the apparatuses. Based on the facts that strains and defects generally exist in superconductors and the urgent desire on theoretical predictions during the developments of large-scale superconducting structures, this doctoral dissertation develops a series of numerical models to study the complex electromagnetic and mechanical characteristics in several typical superconducting materials and structures.Firstly, combining the Maxwell equations and highly nonlinear superconducting E -J electromagnetic constitutive relationship, the general numerical methods for solving the onedimension, two-dimension and two-dimension axisymmetric time-dependent electromagnetic fields in high-temperature superconductors（HTSs） under the temperature zone of liquid nitrogen are built on the basis of the finite difference theory and finite element theory, which are validated by the experimental results. Particularly, the heat conduction equation is added into the governing equations of the one-dimension problem in order to clarify the influence of the magnetothermal coupling. Based on the numerical methods, I investigate the strains and defects influences on the electromagnetic behaviors and AC losses in typical HTSs such as the slab, round wire and rectangular bulk in AC external field or AC transport current conditions. The dynamic evolutions of the electromagnetic field distributions are given. The simulation results indicate that: whether the magnetic field can fully penetrate the superconductor is the key factor to determine the AC loss dependence on the strain; the effect of the defect position on the AC loss is different in externalfield condition and self-field condition; it is necessary to use the modified E -J power-law relationship for the accuracy of simulating the strong local enhancement of the current density in the vicinity of flaws.Secondly, an anisotropic bulk model is proposed and solved with the established twodimension axisymmetric numerical approach to study the electromagnetic characteristics and AC losses in REBCO high field coils. By the quantitative analysis one verifies that the magnetic shielding effect is a non-ignorable key factor in the electromagnetic simulations of REBCO high field coils. The AC loss characteristics of the coil are investigated in detail, including the spatial distribution of the AC loss in the coil structure and the AC loss dependences on some key parameters（the critical current, n-value and ramp rate of the applied current）. The simulation results are also compared with the experimental data. The validation of several existing analytical methods for the AC loss estimation of the coil is discussed according to the quantitative calculation. In addition, I investigate the property of the coil central field by the established electromagnetic model, in which an optimal approach is proposed to suppress the drift and deviation of the central field.Finally, for the problem of the International Thermonuclear Experimental Reactor（ITER） Cable-in-Conduit Conductor（CICC） subjected transverse loads, an equivalent structural mechanics model is proposed to quantitatively study the two-dimension mechanical characteristics in the cable cross section. The model is validated by comparing the cable transverse mechanical-compression displacement–force curve between the simulation and experimental results. The contact mechanical characteristics among Nb₃Sn strands in the cable cross section are analyzed in detail by the statistical approach, including the average contact forces in subareas and the magnitude distribution of contact force. The results show that the distribution characteristics of contact force depend on the load type. Both the spacial distribution of the average contact force in subareas and the magnitude distribution of contact force in the cable are obviously different for the cases of the electromagnetic load and mechanical load. In addition, the normal force components play the main role in the contact forces distributed in the cable for both cases of loads.