Experiment And Simulation Of Levitation Characteristics Of REBCO Coated Conductor In Permanent Magnetic Fields

High temperature superconducting(HTS)levitation technology is one of the hot points in the investigation of magnetic levitation due to its characteristics of non-friction,little noise and self-stability.Most of traditional study of HTS levitation mainly focus on the system consisted of HTS bulk and permanent magnet(PM),since the special flux pinning of superconductor enables the bulk to levitate above PM stably.However,there exists some shortcomings of bulks,such as small size,low critical current density,poor thermal stability and mechanical strength,being easy-corroded by moisture and hard to store,brittleness.Coated superconductor is a multi-layer structure,constructed by layers of silver,copper,superconductor and stable buffer,which could overcome the drawbacks of bulks,particularly,the manufacturing technique of coated superconductor is more advanced and ensures the properties of uniform critical current density,reproducible and stability of coated superconductor.Nowadays,the application investigation of coated superconductor is becoming a popular topic.For HTS levitation field,the feasibility of coated superconductor has been verified,however,its levitation performance in external field produced by PM should be further revealed,especially for its vibration response to external stimulation.In this paper,we studied the quasi-static levitation properties of coated superconductor in PM fields by means of simulation and experiment,revealed the relationship between levitation performance and the relative position of magnetic field components and stack coated superconductor.In order to change the combinations of stacks and the relative position of external field and the conduction plane of coated superconductor,three identical stacks were manufactured based on modularization design method.A numerical model to calculate the levitation performance of coated superconductor was established based on H-formulation,combining with the non-linear E-J property of superconductor and the homogenization technique to deal with the high aspect ratio of coated superconductor which will lead to a huge computation time and poor convergence.The levitation,guidance forces and force relaxation of different combinations of coated superconductor levitated over two kinds of PM guideways were measured by a self-developed three dimensional multiphysics test rig,and the good agreement of simulation and measured results verified the effectiveness of the numerical model.It was observed from the experiment and simulation results that the perpendicular field contributes to the levitation force whereas the parallel field is responsible for the guidance force,however,the proportion of levitation and guidance forces could be adjusted when the assembly of stack modules was designed properly according to external field,which will realize the coated superconductor levitating over PM guideway stability.Additionally,a vibration test rig which can simultaneously measure the acceleration and levitation force was designed,and three typical excitations,viz.,unloading,free fall and pulsed excitation were applied to reveal the response characteristics of coated superconductor.The damping performance of coated superconductor was analyzed by free vibration attenuation method,and the results demonstrated that the metal components of coated superconductor could act as damping element.When a strong external stimulation was imposed on the levitation system,coated superconductor seems be in alternate magnetic field with a high frequency,and the large resistivity of metal layers contribute to dissipate the energy which helps a faster convergence of the magnetic levitation system.