Electromagnetic waves emitted from an electron-positron plasma cloud moving across a magnetic field

We have investigated the dynamics of an electron-positron plasma cloud moving perpendicular to an ambient magnetic field in a vacuum and also with background plasmas using a three-dimensional electromagnetic particle code. Simulation results show that charge sheaths are formed at both sides of the cloud and a polarized electric field is created inside the cloud by the coherent motion of cloud particles. This polarized electric field leads to the E×B drift motion of the cloud, and some of the cloud particles expand along the magnetic field from the charge sheaths. Consequently, linearly polarized electromagnetic waves are excited from the cloud. It should be noted that the kinetic energy of clouds is transformed very efficiently into the emitted wave energy during about one cyclotron period. This mechanism may be responsible to the emission of strong electromagnetic waves observed in electron-positron plasmas. © 1996 The American Physical Society.