SPATIAL STRUCTURE AND TIME EVOLUTION OF THE WEIBEL INSTABILITY IN COLLISIONLESS INHOMOGENEOUS PLASMAS

The magnetic field generated in an initially unmagnetized and anisotro pic inhomogeneous plasma by the development of the Weibel instability is strongly nonuniform. For the case of a plasma where the anisotropy arises from two (relativistic) counterstreaming electron beams it is s hown, both analytically and numerically, that this instability develop s a spatial ''resonant''-type singularity. The largest magnetic held i s generated around this singularity and has opposite polarities. In th e case of one-dimensional (1D) perturbations, a current layer is forme d very rapidly at the resonance position, almost independently of the characteristic scale of the initial perturbation. In 2D, numerical sim ulations show that a chain of current vortices is formed.