ABSTRACT
Historically, electron plasma waves, or Langmuir waves, were those studied first by the kinetic plasma model. It might not be these waves which are the most interesting, or the most relevant, for plasmas in nature, but taking these as a reference model for discussing some of the basic problems distinguishing a fluid and a kinetic description. In this chapter, the authors have demonstrated that in spite of its time reversibility, the Vlasov equation contains solutions which are damped in time. This is in a “certain sense” only; after all, the Vlasov equation is for the distribution function, and they observe the damped solutions by studying the fluctuations in plasma density or electrostatic potential, which contain reduced information. The linear theory applies for times until the acceleration or deceleration due to the wave-particle interaction changes the particle orbits significantly from the unperturbed orbits.
