Research On Magnetostriction Of High Temperature Superconductor Under Non-uniform Magnetic Field

Since the Netherlands physicist Onnes found superconductivity in 1911,people have deeper understanding of the characteristic of zero resistance effect,meissner effect and Joseph effect,and the superconducting material has been widely applied in various fields.High temperature superconductor(HTS)is a brittle material with many defects.In application it often suffer complex external environment,such as the changeful external magnetic field,transport current and environment temperature.The magnetostriction will appear during the magnetization process because of the magnetic flux pinning force.The micro cracks in superconductors can be expanded by the stronger magnetostrictive effect.When the micro cracks expand to a certain extent,the superconducting materials with low tensile strength will be destroyed.With the increasing of the critical current density and the frequency and amplitude of the magnetic field generated by the electromagnet,the electromagnetic force in superconductors will increase during the magnetization process.This will lead to the result that magnetostrictive effect in the superconductors become more obvious.In this paper,the magnetostrictive problem of rectangular cross section of HTS have been studied based on the finite element method(FEM)and the critical state Kim model.We have numerically simulated the magnetostrictive of the HTS and the homogeneous superconducting material in non-uniform external magnetic field.We obtain the changing trend of magnetostriction during the magnetization process under the electromagnetic force.Firstly,analysed several factors influencing magnetostriction of the HTS,such as the deviation distance between electromagnet and HTS,the critical current density,the amplitude as well as frequency of the applied field magnetic generated by the electromagnet,The variation of the magnetic force between the HTS and the electromagnet was also calculated.The results show that the inhomogeneity of the applied magnetic field affected the magnetostriction of the superconductor.Secondly,the non-uniform coefficient of elastic modulus was introduced to solve the problem of non-uniform superconducting magnetic field in inhomogeneous magnetic field.Meanwhile,several influencing magnetostriction of non-uniform superconducting material have been analyzed,such as the heterogeneity of elastic modulus in HTS,the deviation distance between the superconductor and the electromagnet,the critical current density,as well as the applied magnetic field generated by the electromagnet.Finally,the current distribution and the magnetic flux lines distribution under three different situations have been studied,which is HTS in non-uniform field,non-uniform superconducting material in non-uniform field and high temperature superconductor in uniform field.We found that the distribution of magnetic flux lines with unique features under three different situations.