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

It is shown by using a two-dimensional fully electromagnetic and relativist ic particle-in-cell code that magnetic field energy can be strongly dissipa ted when external plasma flow interacts with the force-free magnetic field configuration in pair plasmas. During the early stage of the interaction, t he streaming instability occurs, which induces the electromagnetic perturba tions associated with the generation of a quasistatic magnetic field. In th e nonlinear stage, the force-free magnetic field becomes unstable against t he firehose instability, and then magnetic islands are formed through magne tic reconnection. The dissipated magnetic field energy is converted to plas ma 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 pl asma flow velocity becomes relativistic (0.9c), the effective energy conver sion from the initial magnetic field energy is observed, with a conversion rate of about 90%. The interaction process between the force-free collision less plasmas and the relativistic plasma flows may play an important role f or effective magnetic field energy conversion, formation of filament struct ures, and high-energy particle production in astrophysical plasmas. (C) 200 1 American Institute of Physics.