Dynamics of plasma bunches in slowly varying external fields

We use the quasineutrality approximation and the method of moments to analyze a system of kinetic equations that describes the expansion into vacuum of a plasma bunch generally containing several species of charged particles. For a two-component collisionless plasma in slowly varying external potential fields, we obtain a complete description of the dynamics of the matrices of centered second moments of the particle velocity distribution functions. We construct a new class of self-similar solutions of the kinetic equations in which the moments of the distribution functions act as parameters. These solutions are found to be valid for any mass and energy ratios of the constituent particles and generally describe the dynamics of a plasma bunch that is asymmetric in space. For a symmetric bunch we also find an analytical solution corresponding to the presence of eddy electric currents in the plasma, while for an asymmetric bunch we find that interparticle collisions, which give rise to anisotropy in the process of expansion of plasma into vacuum, play an important role. The method developed in the paper is used to study the acceleration and compression of a plasma bunch in time-dependent magnetic fields with a mirror configuration. © 1999 American Institute of Physics.