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 als o with background plasmas using a three-dimensional electromagnetic pa rticle code. Simulation results show that charge sheaths are formed at both sides of the cloud and a polarized electric field is created ins ide the cloud by the coherent motion of cloud particles. This polarize d electric field leads to the E x B drift motion of the cloud, and som e of the cloud particles expand along the magnetic field from the char ge 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 d uring about one cyclotron period. This mechanism may be responsible to the emission of strong electromagnetic waves observed in electron-pos itron plasmas.