IPIC3D Simulation Of The Dynamic Processes In Asymmetric Magnetic Reconnection

Magnetic reconnection can change the topology of magnetic field lines and converts energy stored in the magnetic field to particle energy rapidly.Thus,there are many explosively energetic phenomena associated to magnetic reconnection in space and laboratory plasmas.In the magnetosphere of the Earth,magnetic reconnection occurring on the magnetopause can further trigger that on the magnetotail,which is thought to be the main reason for magnetic storm,magnetic substorm and other space weather phenomena.In addition,in the magnetically controlled fusion plasmas,several instabilities caused by magnetic reconnection can lead to confinement degradation.Therefore,research on magnetic reconnection will improve our understanding of it and guide human being’s activities in space exploration and development of clear energy source in the meantime.Magnetic reconnection is asymmetric at the magnetopause,due to the completely different properties of the plasmas on both sides of the reconnection current sheet.In addition,the reconnection process will be more complicated when the guide field gets involved,which is caused by east-west component of solar wind.PIC method can be used to simulate the behaviors of electrons and ions separately and the implicit algorithm will remove the limit of numerical stability.Hence,particle dynamics in the processes of symmetric and asymmetric magnetic reconnections have been investigated with implicit PIC method in this work.Magnetic reconnection in a symmetric current sheet configuration has been simulated at first.The evolution of reconnection rate over time and the peak value of reconnection rate are abtained,and a quadrupolar Hall magnetic field structure perpendicular to the reconnection plane is found to near the separatrix.These results manifest the correctness of the program used.Besides,in the inflow and outflow regions,both distributions of ions and electrons deviate from Maxwellian type in their phase spaces.Next,by setting different configurations of initial current sheets,the magnetic reconnections under the current sheet with different asymmetry degrees have been investigated.It is found that magnetic reconnection rate will decrease as the increase of the degree of asymmetry of current sheet.In the reconnection plane,The curvature of the magnetic field lines on the high-density side of the weak magnetic field is greater than that on the low-density side of the strong magnetic field.At the same time,the electric field,magnetic field,and current all exhibit varying degrees of asymmetry.Furthermore,as the degree of asymmetry increases,the ion inflow becomes smaller and smaller,while the inflow of inos on the low-density side becomes weaker than the other side.Simultaneously the electron flow field is no longer symmetric,which terns the quadrupolar Hall magnetic field structure into a bipolar one.Furthermore,electrons in the outflow region at low-density side have a wider distribution in their phase space because of the acceleration in the out flow region at highdensity side.Finally,the guiding field is introduced into the symmetric and one of asymmetric system.It is found that guiding field will derease magnetic reconnection rate,but it has a relatively small influence on the reconnection rate of asymmetric situation.When the guiding field is added in the symmetry system,the structrue of the electromagnetic field and flow field undergo significant changes,but they all keep symmetric around the origin.While adding guiding field in an asymmetric system the overall structures no longer have any obvious symmetry and will cause the drift of the magnetic separatrix takes place.At this time,the Hall magnetic field structure outside the reconnection plane changes,but it is still determined by the electron flow field.The analysis of velocity distributions of elctrons and ions reveals that both distributions of electrons and ions are strongly anisotropic when the guiding field is added.