Signal propagation in collisional plasma with negative ions

The transport of charged species in collisional currentless plasmas is trad itionally thought of as a diffusion-like process. In this paper, it is demo nstrated that, in contrast to two-component plasma, containing electrons an d positive ions, the transport of additional ions in multispecies plasmas i s not governed by diffusion, rather described by nonlinear convection. As a particular example, plasmas with the presence of negative ions have been s tudied. The velocity of a small perturbation of negative ions was found ana lytically and validated by numerical simulation. As a result of nonlinear c onvection, initially smooth ion density profiles break and form strongly in homogeneous shock-like fronts. These fronts are different from collisionles s shocks and shocks in fully ionized plasma. The structure of the fronts ha s been found analytically and numerically. (C) 2001 American Institute of P hysics.