Distribution Of Chaos-induced Resistivity In Collisionless Magnetic Reconnection Current Sheet

As an effective mechanism of magnetic energy release,magnetic reconnection has been widely used to explain various plasma eruptive phenomena such as solar flares and geomagnetic storms.However,some key dynamic processes of the reconnection current sheet,especially the microphysical mechanism of anomalous resistivity in the collisionless magnetic reconnection,are still unsolved.Among many physical mechanisms related to anomalous resistivity formation,chaos-induced resistivity based on the chaos of the charged particle orbits near the magnetic neutral point in the reconnection region is not the most popular formation mechanism,but it is the most clear microscopic physical image generation mechanism.From 1998 to 2003,Japanese scholars Yoshida and Numata et al.first proposed and studied the“resistivity”effect of the randomization of the directional motion of current-carrying particles caused by the chaos of the charged particle orbits near the X-type magnetic neutral point,and called "chaos-induced resistivity".In 2014,Andriyas and Spencer conducted a simulation study on the observed characteristics of the magnetotail reconnection region and found that this chaos-induced resistivity mechanism may make an important contribution to the generation of anomalous resistivity in the magnetotail reconnection current sheet.In 2017,Shang(Meng Shang)et al.further extended the work of Yoshida and Numata et al.to cases with non-zero guide field in the X-type magnetic neutral point.Considering the complex topological structure of magnetic field and current distribution in the actual reconnection region,this thesis systematically studies the distribution characteristics of chaos-induced resistivity in collisionless magnetic reconnection region with different current sheet configurations,and discusses their contribution to the generation of anomalous resistivity in different magnetized plasma environments such as corona and solar wind.In the first chapter of the thesis,the relevant scientific background and research status of collisionless magnetic reconnection,anomalous resistivity and chaos-induced resistivity are briefly introduced.In the second chapter of the thesis,the X-type magnetic neutral point case studied by Shang et al is extended to finite width uniform reconnection current sheet with double Y-type magnetic configuration.The results show that the distribution of chaos-induced resistivity in the reconnection current sheet is inhomogeneous,mainly distributed in the Ytype dissipation region near the two sides of the reconnection current sheet,which is one order of magnitude higher than the core region in the middle of the reconnection current sheet.Meanwhile,the analysis of the environmental parameters of coronal plasma shows that the chaos-induced resistivity in Y-type dissipation region can be increased by 5-6 orders of magnitude compared with the classical collision resistivity,which can meet the requirements of anomalous resistivity for the rapid release rate of flare energy.Many theoretical analysis and numerical simulation studies have shown that the reconnection current sheet with finite width is often unstable,especially the tearing mode instability will lead to the evolution of the uniform current sheet into an island-chain current sheet with alternating distribution of X-type and Otype magnetic neutral points.Therefore,in the third chapter of the thesis,the distribution of chaos-induced resistivity in inhomogeneous reconnection current sheet with island-chain structure is further studied.The results show that the chaos-induced resistivity in the island-chain current sheet is mainly distributed near the X-type magnetic neutral point,which is 1-2 orders of magnitude higher than near the O-type magnetic neutral point.This is consistent with the previous MHD simulation results showing that the dissipative region and flow region of the island-chain current sheet are mainly concentrated near the X-type and O-type magnetic neutral points,respectively.In addition,some observations show that there are often bifurcation structures of double current sheets in the magnetotail and interplanetary plasma environments.For example,Chian et al.found a double current sheet structure formed by the interaction of triple coronal mass ejections in the interplanetary solar wind,and their analysis results show that there are strong intermittent turbulence in the central region of the double current sheet structure.In the fourth chapter of the thesis,the distribution characteristics of chaos-induced resistivity in double current sheet structure are also analyzed and studied.Based on the corresponding measurement parameters,the results show that the chaos-induced resistivity in the region of intermittent turbulence is 2 orders of magnitude higher than that outside,which means that the chaos-induced resistivity may be an important reason for the formation of intermittent turbulence.Finally,the fifth chapter of the thesis gives a brief summary and prospect of the research work.The results of this thesis show that chaos-induced resistivity is a direction worthy of further research for the generation mechanism of anomalous resistivity in the collisionless magnetic reconnection.