Nonlinear models for Langmuir waves in a collisionless plasma

Abstract

In this study we have performed analytical and numerical analysis of electron density oscillations, known as Langmuir waves, in collisonless plasmas. Such oscillations are important in both experimental and astrophysical plasmas. We have generalized the standard fluid description to include basic features of thermal- and nonlinear- effects. Through the so-called multiple water-bag model we also attempt to include Landau damping in the fluid model. This is advantageous as Landau damping is a kinetic phenomenon, and generalized fluid models are computationally more efficient than the kinetic alternative. For linear Langmuir waves we obtain a good reproduction of Landau damping by the multiple water-bag version of the fluid model. The damping is, however, strongly dependent on the chosen initial conditions for the electron density oscillations. Nonlinear analysis through the inclusion of ponderomotive forces and a special version of the Zakharov model are not as easily solved in the context of multiple water-bags. We also find that Landau damping will be more difficult to extract from this generalized nonlinear model than for the linear waves.