Research On Analytical Theory Of Magnetic Reconnection

Magnetic reconnection,as a fundamental physical process that converts electromagnetic energy into plasma energy,occurs widely in laboratory and various space plasma enviroment,and it plays a critical role in many important kinetic processes.It not only involves the magnetospheric dynamics that contains the coupling mechanism between the solar wind and magnetosphere,but plays an important part in the realization of the energy of magnetically confined plasma fusion.Therefore,investigating the reconnection process is quite helpful to understand the explosive phenomena,as well as the complex dynamic process.Such as solar flares and turbulence.Since the complex and diverse interaction between magnetic field and plasma in three-dimensional space,the analysis and dynamic process of three-dimensional magnetic reconnection has been the frontier topic in physics.The traditional analytical theories of three-dimensional magnetic reconnection don't consider the change of time,while the analytical theories considering the change of time don't discuss the interactions between magnetic field and plasma.Besides,current analytical theories rely too much on the configurations of magnetic field or flow field,and don't discuss the general situation.Due to the limitations of the existing analytical methods,this thesis systematically analyses the characteristics of plasma flow in time-dependent systems by considering the time factor in the theoretical equations,and then the magnetic field configurations are generalized and extended to discuss the existence of steady plasma flow in time-dependent systems.The main research results are as follows:In the time-dependent magnetic diffusion coefficient model,the plasma flow is concentrated in a small area near the center point prsenting a distribution of counterrotating flows above and below the reconnected region,and the overall configuration of the flow field does not change.Due to the coupling of theoretical equations,the invovled of time factor only changes the velocity but not the distribution of flow field.In the time-dependent magnetic field model,the plasma flow in the small scale presents a "four-asymmetry" distribution or a "helical radial" distribution,both of which gradually disperse at any time in space scale.It is found that the magnetic vector potential is the main physical factor that affects the velocity distribution of plasma flow in the time-dependent model.The implicit function forms of plasma flow velocity respecting to time and space variables in general time-dependent systems are derived for the first time.The existence of steady plasma flow in time-dependent systems is preliminarily analyzed.The above analysis reveals that the steady flow is difficult to exist in time-dependent systems.It shows that only 29 kinds of steady flow existence conditions exist in the time-dependent system.Further more,all 29 conditions were analyzed,and only 5 of them have special physical significance.One of the conditions is only constrained by spatial variables,while the other four conditions correspond to specific solutions of some time factors.Finally,those conditions are applied to the problem of traditional magnetic reconnection.These studies are helpful to enhance our understanding of the temporal and spatial variation of magnetic field,the interactions between magnetic field reconnection and plasma flow,and the energy conversion process in magnetic field reconnection.