Roles of initial current carrier in the distribution of field-aligned current in 3-D Hall MHD simulations  

作　　者：ZHANG XianGuo PU ZuYin MA ZhiWei ZHOU XuZhi 

机构地区：[1]Institute of Space Physics and Applied Technology,School of Earth and Space Science,Peking University,Beijing 100871,China [2]Institute of Plasma Physics,Chinese Academy of Sciences,Hefei 230031,China [3]Institute of Fusion Theory and Simulation,School of Science,Zhejiang University,Hangzhou 310027,China

出　　处：《Science China(Technological Sciences)》2008年第3期323-336,共14页中国科学（技术科学英文版）

基　　金：Supported by the National Natural Science Foundation of China (Grant Nos. 40474058 and 40536030);the Key Project of the National Natural Science Foundation of China (Grant No. 40390152);Chinese Fundamental Research Project (Grant No. G200000784);Chinese Key Research Project (Grant No. 2006CB805305);the Key Displine Project of Beijing

摘　　要：A three-dimensional (3-D) Hall MHD simulation is carried out to study the roles of initial current carrier in the topology of magnetic field, the generation and distribu- tion of field aligned currents (FACs), and the appearance of Alfvén waves. Consid- ering the contribution of ions to the initial current, the topology of the obtained magnetic field turns to be more complex. In some cases, it is found that not only the traditional By quadrupole structure but also a reversal By quadrupole structure appears in the simulation box. This can explain the observational features near the diffusion region, which are inconsistent with the Hall MHD theory with the total ini- tial current carried by electrons. Several other interesting features are also emerged. First, motions of electrons and ions are decoupled from each other in the small plasma region (Hall effect region) with a scale less than or comparable with the ion inertial length or ion skin depth di=c/ωp. In the non-Hall effect region, the global magnetic structure is shifted in +y direction under the influence of ions with initial y directional motion. However, in the Hall effect region, magnetic field lines are bent in ?y direction, mainly controlled by the motion of electrons, then By is generated. Second, FACs emerge as a result of the appearance of By. Compared with the prior Hall MHD simulation results, the generated FACs shift in +y direction, and hence the dawn-dusk symmetry is broken. Third, the Walén relation in our simulations is consistent with the Walén relation in Hall plasma, thus the presence of Alfvén wave is confirmed.A three-dimensional (3-D) Hall MHD simulation is carried out to study the roles of initial current carrier in the topology of magnetic field, the generation and distribution of field aligned currents (FACs), and the appearance of Alfvén waves. Considering the contribution of ions to the initial current, the topology of the obtained magnetic field turns to be more complex. In some cases, it is found that not only the traditional B y quadrupole structure but also a reversal B y quadrupole structure appears in the simulation box. This can explain the observational features near the diffusion region, which are inconsistent with the Hall MHD theory with the total initial current carried by electrons. Several other interesting features are also emerged. First, motions of electrons and ions are decoupled from each other in the small plasma region (Hall effect region) with a scale less than or comparable with the ion inertial length or ion skin depth d i =c/ω p . In the non-Hall effect region, the global magnetic structure is shifted in +y direction under the influence of ions with initial y directional motion. However, in the Hall effect region, magnetic field lines are bent in ?y direction, mainly controlled by the motion of electrons, then B y is generated. Second, FACs emerge as a result of the appearance of B y . Compared with the prior Hall MHD simulation results, the generated FACs shift in +y direction, and hence the dawn-dusk symmetry is broken. Third, the Walén relation in our simulations is consistent with the Walén relation in Hall plasma, thus the presence of Alfvén wave is confirmed.

关 键 词：COLLISIONLESS magnetic RECONNECTION HALL MHD simulation field ALIGNED current (FAC) Alfvén wave HALL effects 

分 类 号：TP391.9[自动化与计算机技术—计算机应用技术]