Particle acceleration during the counterstreaming instability in magnetized pair plasmas

Abstract

The electromagnetic counterstreaming instability in unmagnetized pair (electron-positron) plasmas, which is influenced by the external magnetic field parallel to the streaming direction, is investigated both analytically and numerically. It is shown from the linear theory of relativistic cold four fluids model that the generation of a quasi-static magnetic field whose wave vector is perpendicular to the streaming direction is restrained by the increasing external magnetic field. The linear theory is also confirmed by particle-in-cell simulation. The theory and simulation show that the counterstreaming instability changes its character from magnetic to electrostatic nature when the external magnetic field increases as ωce>1.5ωpe. The electrostatic waves growing due to the electrostatic counterstreaming instability play an important role for producing fast electrons and positrons with energy of MeV. The process of high-energy particle production in relativistic shocks in magnetized pair plasmas may be applied to gamma-ray burst events.