Scientists Uncover Electron-Scale Quadrants of the Hall Field in Magnetic Reconnection

  • [2017-05-04]
    Magnetic reconnection has been believed to be responsible for a large number of explosive phenomena in space, astrophysics, and laboratory plasmas. Because it is an effective mechanism for converting magnetic energy into plasma kinetic and thermal energy. Because of the Hall effect, ions are unmagnetized and electrons are magnetized in reconnection ion diffusion region. The relative motion between ions and electrons results in a quadrupole pattern of the out-of-plane magnetic field and a bipolar pattern of the Hall electric field pointing to the center at both sides of the reconnecting current sheet. However, this quadrupole pattern will be replaced by a bipolar pattern in asymmetric reconnection as suggested in simulations. On the other hand, it is a long outstanding issue that what is happening inside electron diffusion region.

    Now, Prof. LU Quanming’s group find unexpected Hall electric and magnetic field patterns surrounding the electron diffusion region in asymmetric reconnection. They find that the quadrupole pattern of the Hall magnetic field, which is commonly observed in a symmetric reconnection, is still evident in an asymmetric component reconnection, but the two quadrants adjacent to the magnetosphere are strongly compressed into the electron scale and the widths of the remaining two quadrants are still ion scale. The bipolar Hall electric field pattern generally created in a symmetric reconnection is replaced by a unipolar electric field within the electron-scale quadrants.

    Furthermore, they directly identified the inner electron diffusion region based on the violation of the electron frozen-in condition, the energy dissipation, and the slippage between the electron flow and the magnetic field. Within the inner electron diffusion region, magnetic energy was released and accumulated simultaneously, and it was accumulated in the perpendicular directions while dissipated in the parallel direction. It means that the reconnection is not only an energy release process but also a magnetic energy accumulation process.

     

    Figure. Schematic illustration of the reconnection diffusion region(Image by WANG Rongsheng)

    The work was published on Physical Review Letters, entitled as “Electron-Scale Quadrants of the Hall Magnetic Field Observed by the Magnetospheric Multiscale spacecraft during Asymmetric Reconnection” on 28 April. The first author is Dr. WANG Rongsheng. The work was supported by National Natural Science Foundation of China and by the National Basic Research Program of China

    The link of the paper: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.175101

    Contact

    Dr. WANG Rongsheng

    rswan@ustc.edu.cn

     

     

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