Investigations On Mechanical Characteristics And Flux Dynamical Behaviors Of Superconducting Materials And Structures

Due to the high current-carrying capacity in the high magnetic field,the high-temperature superconductors(HTS)are widely used in the scientific equipment,medicine,energy,transportation and other fields.However,the superconductors are subjected to the complex mechanical loads and deformations during operation because of the extreme working environment.This directly affects the electromagnetic property of the superconducting materials and the reliability of the superconducting structures.On the other hand,the slow quench propagation velocity of the HTS leads to that it is difficult for the timely quench detection,and the local temperature rise could cause the quench in the superconducting structures.Therefore,the mechanical response and thermal stability become the core problems which constrain the application and development of the HTS magnets.In this paper,the mechanical behaviors and the quench characteristics of the HTS coils are studied on the macro scale.Meanwhile,the main factors which can affect the flux dynamics of the type-? superconductor are investigated on the mesoscopic scale.Firstly,we build the homogenization model of the REBCO superconducting strip based on the representative volume element(RVE)in micromechanics of composites and obtain the equivalent mechanical and thermal parameters.The size parameters of REBCO coil are selected with the central magnetic field as the target.Then,the mechanical analysis of multi-physics field is performed for the REBCO racetrack coil using the equivalent parameters.The results show that the compression among the strips leads to an obvious hoop and axial stress in the semi-circular part during winding.However,the winding will not cause the obvious radial compression in the linear part.During the cooling process,there is an obvious increasing of the stress and strain in the coil due to the different thermal expansion coefficients of the strip and mandrel.In the process of operation,the stress and strain caused by electromagnetic force is small under the self-field.In addition,it can be seen from the result of the thermal stability analysis that the thermal expansion at the local hot spot is obviously greater than the surrounding area due to the slow quench propagation velocity in the coil.Then,the flux dynamical behaviors and the electromagnetic properties of the type-? superconductors are analyzed based on the time-dependent Ginzburg-Landau(TDGL)equations under the mesoscopic scale.We discuss the effect of the different artificial pinning centers on the electromagnetic properties in the thin current-carrying superconducting strip.The effects of internal holes on the penetration magnetic field of superconducting materials and the motion of flux vortex are discussed based on the TDGL equations and heat diffusion equations.The effect of the thermal effect on the flux dynamics is also discussed.The energy dissipation caused by the vortex motion can lead to a local temperature rise in the superconductors.This can cause that the subsequent vortices tend to move along the trajectories of the previous vortices.Then,we propose a numerical model for the manipulation of the vortex motion using the dynamics heat sources.The relationship between the driving force and the vortex motion is discussed.It is found from the results that the main factor affecting the vortex dynamics and the corresponding electromagnetic behaviors is the synchronous relationship between the driving force and the vortex motion.In addition,the effects of the different distributions of the thickness and metal cover plates with different heat dissipation capacities on the flux dynamical behavior of the 3-D multilayer superconducting films are discussed based on Maxwell equations and TDGL equations.