Flux Concentration Effect And Electromagnetic Simulation Of High Temperature Superconducting Magnetic Lens

High magnetic field is an important environment condition for frontier scientific research,power and energy engineering,medical and water treatment and other fields.The strength of magnetic field of existing high-field magnets has approached the limit of normal conductor and low temperature superconducting(LTS)materials.The development of high temperature superconducting insert magnet has become the trend and key to further increase the magnetic field.However,the preparation process of the insert magnet is complicated and expensive.Therefore,the development of a small,low-cost magnetic field converging device has important scientific value.Among them,the high temperature superconducting(HTS)magnetic flux lens is a new type of passive insert magnet which exploits the induced shielding current to restrict the spatial magnetic field distribution,and hence increasing the local flux density.The device has the advantages of low cost,no loss,safe operation,flexible use,etc.,which is of great significance for local high magnetic field applications where space scale requirements are not high.In this thesis,based on Finite Element Method and combined with the characteristics of superconductors,numerical simulation and magnetic flux concentration effect of the high-temperature superconducting magnetic flux lens are studied.The working environment,magnetization method and geometric structure of the magnetic flux lens are optimized.The main research contents and results are as follows:(1)The numerical model of superconducting magnetic flux lens is established by combining Maxwell's equation and the nonlinear E-J characteristics of superconducting.Based on this model,the paper studies the concentration effect and optimal working conditions of the Gd Ba₂Cu₃O_7-?(Gd BCO)rectangular superconducting magnetic flux lens.The results indicate that the rectangular magnetic flux lens has an optimal geometric aspect ratio and maximum magnetic field increment.At a temperature of 30K and background magnetic field of 11.0 T,a central magnetic field of 17.2 T is obtained in the magnetic flux lens with a gap width of 2 mm.The magnetic field is increased by 56%.(2)A three-dimensional hollow cylindrical Gd BCO superconducting magnetic flux lens model was constructed,and the magnetic flux concentration effects under different excitation methods were calculated.The reported experimental results are well reproduced through numerical simulation calculations.Due to the poor mechanical properties and unstable magnetic flux of high-temperature superconducting bulk materials,fragmentation and magnetic flux jumps are prone to occur during the experiment.The paper also calculated the multi-lobed fragmented magnetic flux lens and found that the fragmentation model still has an outstanding magnetic flux concentration effect.At a temperature of 4.2 K and a background magnetic field of 5.0T,a central magnetic field of 9.9 T is obtained,which is only 1.1 T lower than the central magnetic field of 11.0 T in the original one.(3)A feasible scheme for using stacked YBa₂Cu₃O_7-X(YBCO)superconducting tapes(2G-HTS)with higher critical current density to replace high-temperature superconducting bulk materials to make magnetic flux lenses is proposed.The rectangular and X-shaped stacked superconducting tape magnetic flux lenses are constructed and studied.The results show that the concentration effect of the X-shaped magnetic flux lens is significantly better than the rectangular.Under the conditions of B_a=5 T and T=4.2 K,the rectangular and X-shaped magnetic flux lens B_c reach 6.7 T and 11 T,respectively.When B_a=20 T,the central total magnetic field of the rectangular and X-shaped lenses are 21.2 T and 24.1 T respectively.