MAGNETIC-FIELD GENERATION AND WAVE-BREAKING IN COLLISIONLESS PLASMAS

We discuss the nonlinear evolution of the Weibel instability of two co unter-streaming electron beams in the relativistic and non-relativisti c regimes in the framework of a two-fluid description. We show the pre sence of two singularities per wavelength, responsible for the formati on of very large density spikes. In the case of non-symmetric beams, w e observe the compressive wave-break of the fast electron population, and the generation of a dipolar magnetic field associated with a centr al fast thin current and two larger slow return currents. This structu re is very similar to those observed in PIC simulations of laser-plasm a interactions.