Research On Bitter-like High Temperature Superconducting Magnet Energized By Flux Pump With Multi-plused Magnetic Field

Due to the immature jointing technology of high temperature superconducting(HTS)tape,it is impossible to achieve the persistent current mode(PCM)same as the traditional low temperature superconducting(LTS)magnets.At present,the non-resistive jointing technology of MTS tape is one of the technical bottlenecks.In order to avoid this problem,a new structure of HTS magnet excited by flux pump method is proposed.The new structure of HTS magnet is Bitter-like HTS magnet,which is formed by stacking RcBCO(Re-Ba-Cu-O,Re refers to a rare earth element)annular plates.The Bitter-like HTS magnet has the advantages of small volume,light weight and no current lead.The research is of great significance for HTS magnet to achieve persistent current mode and to generate strong magnetic fields.This thesis proposes a flux pump excitation method that uses electromagnetic induction to provide energy to the magnet.Its principle is similar with that of an air core transformer.The flux pump coil couples the magnetic flux into the Bitter-like HTS magnet without current leads.This excitation technique can be used to achieve HTS magnet operating with PCM.This thesis introduces the fabrication process of ReBCO annular plates,the structure of the Bitter-like HTS magnet,the structure and principle of the flux pump.The excitation process of the Bitter-like HTS magnet was simulated by COMSOL 5.3a software.The simulation results are combined with the experimental results to verify that the flux pump excitation method can realize PCM operation of the Bitter-like HTS magnet.Then,the magnetic field distribution and current density distribution of the ReBCO annular plate are simulated.The exciting effects of the outer excitation mode and the inner excitation mode are experimentally performed.and the optimal length parameter of the coil in flux pump is analyzed and measured.The Bitter-like HTS magnet structure is a potential breakthrough for achieving persistent current mode.The magnetic field distribution and critical current density distribution on the ReBCO annular plates are calculated by MATLAB programming,which lays a foundation for the study of actual current distribution.In the inner excitation mode,the flux pump coil is placed at the center of the Bitter-like HTS magnet.And in the outer excitation mode,it locates at the center of the exciting coil in a pulse magnet.The comparison of both of inner and outer excitation methods results shows that the former excitation method has obvious advantages over the latter one at 77 K liquid nitrogen temperature.The excitation curve of’ the Bitter-like HTS magnet is simulated and tested.The research results indicate that there is an optimal length for flux pump coil.If the coil length is less than the optimum value,the final trapped magnetic field of the Bitter-like HTS magnet increases as the length of the exciting coil increases.If the coil length is further increased beyond the optimum value,the final trapped magnetic field of the superconducting magnet reaches a constant no longer increases.In this thesis,the optimal length choice of the flux pump coil for assembled Bitter-like HTS magnet is obtained and then confirmed.