REDUCED DESCRIPTION OF STRONG LANGMUIR TURBULENCE FROM KINETIC-THEORY

A reduced description of strong Langmuir turbulence is derived from the Vlasov-Poisson equations by using an oscillation center transformation that decomposes the distribution function into envelope components which vary slowly on the plasma frequency time scale. The familiar high-frequency response is identified in the context of a basic ordering of small quantities. A generalization of the ion acoustic wave equation to the regime of equal electron and ion temperatures which is valid in this ordering is derived using a three-pole approximant for the collisionless ion susceptibility. The resulting extended Zakharov model is solved numerically in two dimensions for parameters relevant to radio-frequency heating of the ionosphere, producing energy and power spectra of fluctuations that are qualitatively similar to experimental observations, A new local quasilinear equation for the spatial and temporal evolution of the slowly varying part of the oscillation center distribution function is proposed. © 1995 American Institute of Physics.