Amplification of Magnetic Modes in Laser-Created Plasmas

The amplification of magnetic (Weibel) modes in laser-plasma interaction is investigated by use of unperturbed distribution functions given by Fokker-Planck simulations and a dispersion relation valid for all collisionality regimes. In the five cases studied, a strongly growing mode is found in the underdense plasma, where ${\overline{v}}_x^2<\frac{1}{2}{\overline{v}}_{\perp }^2$, and the usual slowly growing one in the overdense plasma. The first mode grows convectively outwards by more than ${10}^4$. The convection velocities are found to be very different from Nernst values.