Research On In-situ Pulsed Field Magnetization For High-Temperature Bulk Superconducting Machine Applications

REBCO(RE=Y,Gd,Sm,Nd,etc.)quasi-single-domain high-temperature bulk superconductors have unique self-stabilizing levitation characteristics and strong magnetic flux trapping ability,which are used in superconducting flywheel energy storage,superconducting maglev trains and superconducting Motors and other fields have huge application potential.The main magnetization methods of bulk superconductors are field cold magnetization and pulse magnetization: field cold magnetization usually uses a superconducting magnet to generate a constant magnetic field to magnetize the sample,and the magnetization effect is good,but the cost is high,and in-situ magnetization cannot be achieved;pulse field magnetization passes a pulse current to the copper solenoid coil through a capacitor generating a pulsed magnetic field to magnetize a sample has the advantages of simple equipment,low cost,fast magnetization,and in-situ magnetization,and is a more practical way of magnetization.At present,the interaction mechanism between the magnetic field and the superconductor and the magnetic flux dynamics process in the pulsed field magnetization process are still unclear,and there are many difficulties in the physical realization of cooling and magnetization in the system.These are the bottlenecks in the realization of the application of bulk superconductor.In view of the above key issues,the main research contents and results of this paper are as follows:(1)Independently designed and built a set of experimental devices including pulsed magnetic field generation,fixed cooling of samples and dynamic measurement of magnetic flux density to systematically study the magnetization characteristics of bulk superconductors and the dynamic changes of magnetic flux density under pulsed magnetic field.The pulsed magnetic field can reach up to 9.3 T,and has a good linear relationship with the charging voltage,which can realize the fine control of the magnetic field amplitude.(2)The magnetization process of yttrium barium copper oxide bulk magnets was systematically studied,and the magnetization effects of superconducting bulk magnets under field cold magnetization and pulse field magnetization were compared.Studies have shown that the trapped magnetic field of the pulsed field magnetization at 77 K can reach 95% of the field-cooled magnetization.(3)According to the actual application scenario,the pulsed field magnetization study of the combination of two samples was carried out,and the influence of the adjacent samples on the magnetic flux penetration process and the trapped magnetic field during the pulsed field magnetization process was revealed.The research results show that the magnetic shielding effect of the adjacent samples increases the magnetic flux density at the connection position and changes the process of the magnetic flux penetrating the sample.The uneven magnetic flux penetration and heat generation affect the local critical current density of the sample.The trapped magnetic field of the combined sample is slightly smaller than that of the monolithic sample.(4)In-situ magnetization tests and running tests were carried out for a quasi-permanent magnet motor based on high-temperature bulk superconductors.The rotor of the motor contains 4 magnetic poles,each of which is composed of 12 yttrium barium copper oxide bulks.In the experiment,liquid nitrogen was used to cool the superconducting rotor cyclically,and a pulsed magnetic field was generated through the stator winding to realize the overall in-situ magnetization of the superconducting rotor.