Nonlinear filamentation instability driven by an inhomogeneous current in a collisionless plasma

Beams of fast electrons in a cold electron background play a key role in the generation of a magnetic field in the wake of an ultrashort ultraintense laser pulse propagating in an underdense plasma. Here we study the linear and nonlinear evolution of the electromagnetic beam-plasma instability in a collisionless inhomogeneous plasma by using a set of two-fluid electron equations in the nonrelativistic and relativistic regimes. We show the characteristic spatial structures in the current and magnetic field distributions that are generated by this instability. These structures can be used as a signature of the physical mechanism at play in the analysis of the numerical and experimental results of the laser-plasma interaction. [S1063-651X(98)05412-9]