电子重联中电磁场结构的粒子模拟  

Particle-in-cell Simulation of Electromagnetic Field Structure in the Electron-only Reconnection

作　　者：胡市航 陆全明[1] 关云丹 卢三[1] HU Shihang;LU Quanming;GUAN Yundan;LU San(School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026)

机构地区：[1]中国科学技术大学地球和空间科学学院,合肥230026

出　　处：《空间科学学报》2024年第6期970-978,共9页Chinese Journal of Space Science

基　　金：国家重点研发计划项目资助(2022YFA1604600)。

摘　　要：采用2.5D全粒子模拟程序研究了强引导场情况下的电子重联,分析了重联率最大时刻霍尔磁场、霍尔电场及电子流速的空间分布特征.重联率最大时刻,观察到分离线两侧的电子入流及出流,并且有四极霍尔磁场生成.与早期标准重联的研究结果不同,霍尔磁场并未在引导场的作用下发生明显扭曲.同时分离线区域发生电荷分离,并生成近似对称分布的霍尔电场.此外,研究了电子流速空间分布的时间演化.在重联前期,电子主要沿磁力线流动,即ve≈v_(ey)B/B_(y);在重联后期,电子运动由电场漂移所主导,即ve≈E×(B_(y)e_(y))/B_(y)^(2).模拟结果表明,电子重联中可以发生极强的电荷分离,生成近似对称分布的霍尔电场.在引导场下,这种霍尔电场将导致电子的电场漂移,并主导电子流速的面内空间分布,进而生成近似对称分布的霍尔电流和四极霍尔磁场.Standard collisionless magnetic reconnection couples with both electron and ion dynamics.Recently,a new type of magnetic reconnection,electron-only magnetic reconnection without ion outflow,2.5has been observed.Using D particle-in-cell simulation,the electromagnetic field structure in the elec-tron-only reconnection with a strong guide field was studied.At the moment of the maximum reconnec-tion rate,the electron inflow and outflow are observed on either side of the separatrix.The spatial distri-bution of the electron bulk velocity is approximately symmetric,which generates the nearly symmetrical-ly distributed Hall current,resulting in the quadrupole Hall magnetic field.The Hall magnetic field is not obviously distorted despite the presence of the strong guide field.Meanwhile,the charge separation is caused in the separatrix region,which generates the nearly symmetrically distributed Hall electric field.Besides,the evolution of the spatial distribution of the electron bulk velocity was studied.The equation ve=veyB/By+E×(Byey)/B2yof motion for the frozen electrons was analytically obtained:.According to the equation of motion for the electrons,we divide the electron-only reconnection with a strong guide E×Bfield into two stages.In the first stage,the drift is negligible because of the weaker Hall electric field,and then the electrons flow mainly along the magnetic field line following the equation ve≈veyB/By E×B ve≈E×(Byey)/B2yinated by the.In the second stage,the Hall electric field is so strong that the motion of electrons is dom-drift following the equation.The simulation shows that ex-tremely strong charge separation can be caused in electron-only reconnection,which generates the near-ly symmetrically distributed Hall electric field.With a guide field,this Hall electric field leads to the E×B drift,which dominates the spatial distribution of the electron bulk velocity.Therefore nearly symmetrically distributed Hall current is formed,which generates the nearly symmetrically distributed quadrupole Hall

关 键 词：电子重联 霍尔磁场 霍尔电场 电子流速 

分 类 号：P354[天文地球—空间物理学]