Rapid dissipation of magnetic field energy driven by plasma flows in force-free collisionless pair plasmas

Abstract

It is shown by using a two-dimensional fully electromagnetic and relativistic particle-in-cell code that magnetic field energy can be strongly dissipated when external plasma flow interacts with the force-free magnetic field configuration in pair plasmas. During the early stage of the interaction, the streaming instability occurs, which induces the electromagnetic perturbations associated with the generation of a quasistatic magnetic field. In the nonlinear stage, the force-free magnetic field becomes unstable against the firehose instability, and then magnetic islands are formed through magnetic reconnection. The dissipated magnetic field energy is converted to plasma heating, as well as high-energy particle production. The energy spectrum in the high-energy region shows a law of the exponential type. When the plasma flow velocity becomes relativistic (0.9c), the effective energy conversion from the initial magnetic field energy is observed, with a conversion rate of about 90%. The interaction process between the force-free collisionless plasmas and the relativistic plasma flows may play an important role for effective magnetic field energy conversion, formation of filament structures, and high-energy particle production in astrophysical plasmas.