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    The generalized Ohm's law in collisionless magnetic reconnection

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    Author
    Cai, Heng-Jin
    Chair
    Lee, L. C.
    Committee
    Jiang, T. M.
    Morack, J. L.
    Sentman, D. D.
    Swift, D. W.
    Keyword
    Plasma physics
    Geophysics
    Metadata
    Show full item record
    URI
    http://hdl.handle.net/11122/9418
    Abstract
    Magnetic reconnection is an important process in space environments. As a result of magnetic reconnection, the magnetic field topology changes, which requires the breakdown of the frozen-in condition in ideal magnetofluids. In a collisional plasma, the resistivity associated with Coulomb collisions of charged particles is responsible for the breakdown of frozen-in condition. In a collisionless plasma, however, the cause of the breakdown of frozen-in condition remains unanswered. We address this problem by investigating the generalized Ohm's law and the force balance near magnetic neutral lines based on two-dimensional particle simulations. In a particle simulation with one active species, it is found that a weakly anisotropic and skewed velocity distribution is formed near the magnetic X line, leading to the presence of off-diagonal elements of plasma pressure tensor. The gradients of the off-diagonal pressure terms transport plasma momentum away from the X line to balance the reconnection electric field. The presence of the reconnection electric field results in the breakdown of frozen-in condition. The importance of both electron and ion off-diagonal pressure tensor terms in the generalized Ohm's law near neutral lines is further confirmed in full particle simulations. The generation of the off-diagonal pressure terms can be explained in terms of the thermal dispersion of particle motions and the response of particle distribution function in the electric and magnetic fields near the neutral lines. In the particle simulations, we also find the presence of a new dynamo process, in which a large amount of new magnetic flux near the magnetic O line is generated. This dynamo process is not allowed in resistive magnetofluids. However, in a collisionless plasma, the plasma inertia and momentum transport due to the off-diagonal plasma pressure terms can lead to E $\cdot$ J < 0 near the magnetic O line and make the dynamo process possible.
    Description
    Dissertation (Ph.D.) University of Alaska Fairbanks, 1995
    Date
    1995
    Type
    Dissertation
    Collections
    Physics

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