Nonlinear Modulational Stability and Propagation of an Electromagnetic Pulse in a Two-Component, Neutral Plasma.

摘要

Nonlinear effects are studied including possible modulational instability of an intense electromagnetic pulse propagating through a fully-ionized, unmagnetized plasma. The envelope is shown to evolve over long time scales in general according to a vector form of the well-known cubic nonlinear Schroedinger (NLS) equation. Three distinct nonlinear effects contribute terms cubic in the amplitude and thus can be of comparable magnitude: ponderomotive forces, relativistic corrections, and harmonic generation. Influence of an ambient magnetic field on the nonlinear modulational stability of circularly polarized electromagnetic pulses in a two-component, neutral plasma; the nonlinear modulational stability properties of plasma electromagnetic pulses are extended to include the presence of an ambient magnetic field Bo parallel to the direction of propagation. The positive component may consist of either positrons or singularly charged ions, and specific assumptions or approximations are made concerning the mass ratio of the components. Approximate solutions are derived which describe the evolution of a circularly polarized pulse. The envelope is shown to evolve over long time scales according to the cubic nonlinear Schroedinger (NLS) equation. (JHD)