Generation of magnetic field and electrostatic shock wave driven by counterstreaming pair plasmas

Abstract

By using a two-dimensional (2D) relativistic fully electromagnetic particle-in-cell code, the interaction process of counterstreaming pair (electron–positron) plasmas is investigated. The counterstreaming plasmas become unstable against the collisionless electromagnetic counterstreaming instability, similar to the Weibel instability. In the linear phase, magnetic and electric fields with the scale of skin depth size are generated through the electromagnetic counterstreaming instability. The behavior of plasma in the nonlinear phase is also made clear. The small-scale magnetic fields coalesce with each other, merging through the inverse cascade process which occurs characteristically in 2D dynamics, and change into larger unit. The large-scale magnetic fields propagate more slowly than the initial plasma flow as a low-frequency wave. Behind the magnetic fields, plasmas are isotropically heated by the mixing of counterstreaming plasmas. On the other hand, the electric fields propagate the same as the initial plasma flow. Ahead of the generated magnetic fields, the electric field component along the stream is amplified through the electrostatic counterstreaming instability and the electrostatic shock waves are formed. High-energy particles are also produced from the electrostatic shocks. These simulation results may be applied to the synchrotron gamma-ray burst model.