The ponderomotive force is an important concept in plasma physics and, in particular, plays an important role in many aspects of the theory of laser plasma interactions including current concerns like wakefield acceleration and Raman amplification. The most familiar form of this gives a force on a charged particle that is proportional to the slowly varying gradient of the intensity of a high frequency electromagnetic field and directed down the intensity gradiant. For a field amplitude simply oscillating in time there is a simple derivation of this formula, but in the more general case of a travelling wave the problem is more difficult. Over the years there has been much work on this using Hamiltonian or Lagrangian averaging techniques, but little or no investigation of how well these theories work. Here we look at the very basic problem of a particle entering a region with a monotonically increasing electrostatic field amplitude and being reflected. We show that the equation of motion derived from a widely quoted ponderomotive potential only agrees with the numerically computed orbit within a restricted parameter range and that outside this range it shows features which are inconsistent with any ponderomotive potential quadratic in the field amplitude. Since the ponderomotive force plays a fundamental role in a variety of problems in plasma physics we think that it is important to point out that even in the simplest of configurations standard theories may not be accurate.
We develop a new fluid model of a warm plasma that includes the radiative self-force on each plasma electron. Our approach is a natural generalization of established methods for generating fluid models without radiation reaction. The equilibrium of a magnetized plasma is analysed, and it is shown that the thermal motion is confined to the magnetic field lines. A dispersion relation is deduced for electric waves in a magnetized plasma, and it is shown to agree with our recently established relativistic kinetic theory derived from the Lorentz-Abraham-Dirac equation.
Modern accelerators and light sources subject bunches of charged particles to quasiperiodic motion in extremely
high electric fields, under which they may emit a substantial fraction of their energy. To properly describe the
motion of these particle bunches, we require a kinetic theory of radiation reaction. We develop such a theory
based on the notorious Lorentz-Dirac equation, and explore how it reduces to the usual Vlasov theory in the
appropriate limit. As a simple illustration of the theory, we explore the radiative damping of Langmuir waves.
The notion of a cold Born-Infeld plasma is reviewed and the dispersion relation for a right-handed circularly
polarized electromagnetic plane wave is given. The maximum amplitude (wave-breaking limit) of large amplitude
longitudinal plane waves is summarized.