Study On The Influence Of Magnetic Field Characteristics On The Suspension Properties Of High Temperature Superconducting Bulks

The levitation force of high-temperature superconducting(HTS)bulks has been an important research object in HTS magnetic levitation systems.Researchers in various countries have done a lot of experiments in order to explore the levitation force characteristics of HTS bulks.The experimental results show that the levitation force of HTS bulks will increase with the increase of the external magnetic field.In these experiments,researchers usually place HTS bulks above a permanent magnet guideway(PMG).However,the external magnetic field at the position 15 mm above the PMG(the experimental location of HTS bulks)is only about 0.4 T.In this thesis,we use a superconducting magnet device to generate a high magnetic field of 1 T,2 T and 3 T to carry out the levitation force experiment of HTS bulks.During the pre experiment,it is found that the special magnetic field characteristics inside the superconducting magnet device have a direct impact on the levitation force of HTS bulks.Based on this finding,this thesis conducts a more systematic experimental and simulation study.In terms of experiments,based on the existing 5-T Cryogen-Free Magnet(CRY-CFM-5T-300-H3,Cryogenic Limited),the levitation force test platform was built.The influence of magnetization angle,external magnetic field and external magnetic field gradient on the levitation force of YBa Cu O HTS bulks which were manufactured with a top-seeded multiseeded melt-textured process was studied on the experimental platform,where the magnetization angle θ is specified as the angle between the vertical direction and the normal of the upper surface of the bulks.The results show that the levitation force decreases with the increase of θ from 0 ° to 90 °.Simultaneously,both the increase in external magnetic field and external magnetic field gradient will lead to an increase in the levitation force,but their influence on the levitation force is different.In terms of simulation,this thesis uses the COMSOL Multiphysics to establish a twodimensional axisymmetric geometric model of the 5-T Cryogen-Free Magnet and the HTS bulk.The reciprocating motion of the HTS bulk in the 5-T Cryogen-Free Magnet is simulated,and the curve of the levitation force is given.The simulation results also verify the correctness of the experimental results.Finally,in view of the problem that the radial magnetic field and the magnetic field gradient in the 5-T Cryogen-Free Magnet are too small,which limits the levitation force of the HTS bulk,this thesis proposes a scheme of adding iron core in the 5-T Cryogen-Free Magnet to increase radial magnetic field of the existing high field,and uses the electromagnetic field simulation software Ansoft Maxwell to analyze the radial magnetic field,the magnetic field gradient and the force on the iron core after adding the iron core.According to the analysis results,the specific size and position of the iron core are given,which provides a feasible scheme to increase the levitation force of HTS bulks by optimizing the magnetic field distribution inside the superconducting magnet.