Electron Weibel instability and quasi-magnetostatic structures in an expanding collisionless plasma

We outline transient quasi-magnetostatic phenomena associated with Weibel-type instabilities, mainly the formation and decay of the current filaments and sheets. We consider a collisionless expansion of an anisotropic plasma cloud with hot electrons into a background plasma and take into account an external magnetic field in different geometries entailing (i) a hot-electron spot of a circular or cylindrical form within an initial-value problem or a finite-time injection of electrons from a target surface, (ii) an external magnetic field with three orthogonal orientations: perpendicular to the target or along it, directed either across or parallel to a long axis of the hot-electron spot, and (iii) inhomogeneous layers of cold background plasma of different spatial scales and densities. We heed typical laser-plasma experiments. We outline development of the principal structures of current linked with distinct forms of the anisotropic electron velocity distribution using particle-in-cell modeling of the instability process for diverse sets of the attributes (i)–(iii). Applications to the analysis of laboratory and space plasma problems involving an explosive development of the small-scale self-consistent magnetic turbulence due to filamentation of the electric current are discussed.