The Force-magnetic Characteristics Of Stacked-Tape Magnets Subjected To Travelling Magnetic Field

The linear motor has been developed more than 170 years since it was first proposed and produced by Wheatsone in 1845.Linear synchronous motors(LSM)have been widely used in rail transportation,industry,construction and other industries in recent years due to their large thrust,high reliability and efficiency.Limited by the development of magnetic materials,it is difficult to improve the characteristics of LSM on the original basis.In order to increase the efficiency of LSM through enhancing the magnetic field intensity in air gap,an urgent need is to look for a novel permanent magnetic material with smaller volume and higher remanence to replace the traditional secondary-magnet.Superconductor can trapped high magnetic field generated by the high induced current after field magnetization,and it will be an ideal substitute for traditional secondary-magnet.Given the great potential of the stack of coated conductors which can tapped high magnetic field,the plan of using it as the secondarymagnet for LSM is introduced,thereby to improve the characteristics of linear motor.However,magnetization methods and the total losses have direct influence on the property of stacked magnet(the stack of superconducting tapes which has been magnetized)in practical applications.Therefore,it is necessary to carry out experimental and simulation studies on the electromagnetic properties and force characteristics of coated superconducting stacked magnets subjected to travelling wave magnetic field,to explore the feasibility of its application in ac field applications.Based on the practical problems of stacked-tape magnets in linear motors,the effects of electromagnetic parameters of traveling wave magnetic field and the structure parameters of stacked-tape magnets on trapped flux,attenuation characteristics,force characteristics and the total losses are studied.In the thesis,the magnetization characteristics of stacks of coated superconductors were first studied,and the stacked coating superconductors were magnetized by field cooling.The effect of number of layers on the trapped magnetic flux in stacked-tape magnet was investigated.It was found that trapped filed in stacked-tape magnets increased with the number of layers,then saturated when the stacked number reached a certain value.Meanwhile,the trapped magnetic field becomes saturated with the increase of the external magnetization field.When magnetization current completely penetrates the stacked coated superconductor,the trapped filed inside tape stacks does not increase anymore.And the influence of frequency and amplitude of external magnetic field on trapped field attenuation and force characteristics of stacked tape magnet subjected to travelling-wave magnetic field are experimentally discussed,it is shown that with the amplitude of external magnetic field increasing,the thrust increased but the trapped filed decreased rapidly.However it is worth to note that the field anti-interference ability of stacked tape magnet has been enhanced compared with the superconducting bulk magnet.We present three effective methods to reduce trapped field decay which including: placing superconducting shielding layers at the sides;inserting Permalloy pieces in between;and increasing the number of stacked layers.Finally,in order to further study the loss mechanism of stacked tape magnets subjected to travelling-wave field,the magnetic-thermal coupling model of tape stacks based on the H-formulation is established.The model fully considers the nonlinear E-J characteristics of superconductor and the unique B-J relationship.Based on this model,the influence of the gradient of the travelling magnetic field on the AC losses of the stacked magnet was investigated.The loss distribution was compared in both homogeneous(standing wave field)and inhomogeneous(travelling wave field)magnetic field;and the influence of field gradient(the main parameter is wave length)on the loss was also explored at different external field amplitudes.The feasibility of applying the stacked tape magnet to LSM was demonstrated preliminarily from the experimental and simulation results.The correlational researches provide the fundamental data and design basis for the further development of high-temperature superconducting linear propulsion system prototypes.