Fast Reconnection in Low-density Hydrogen and Pair Plasmas

概要

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Magnetic reconnection without a guide field in low-background-density plasmas has been studied by means of two-dimensional particle-in-cell simulations, and results in hydrogen and electron-positron (pair) plasmas have been compared. Reconnection is impulsive, and maximum reconnection rates of the order of one (measured in units of the Alfvén speed) have been observed in both types of plasmas when the background density in the Harris sheets is 1% of the current sheet density. This impulsive, strong reconnection electric field is important for particle acceleration. As the system evolves in time, the electron diffusion region extends in both inflow and outflow directions. Because of the broadening of the diffusion region, the aspect ratio of the diffusion region remains small, so that fast reconnection is sustained. In pair plasmas, the inertial term in the generalized Ohms law becomes the most dominant term to balance the reconnection electric field before the maximum reconnection rate is attained, which contrasts with hydrogen plasmas where the most dominant term is the pressure tensor term.