Parametric plasma turbulence

Abstract

We present the results of the main papers published during the last few years on the theory of parametric absorption of electromagnetic radiation energy in plasmas. We use the approach of weak Langmuir turbulence theory, since it can be asserted on the basis of the contents of the present paper that this approach is consistent with a wide range of contemporary experiments. The results of the theory of the parametric turbulence of Langmuir and ion-acoustic waves in homogenous plasmas are presented. The shape of the turbulence spectra for different conditions of wave excitation and the properties of the time relaxation of the spectra are discussed. Special attention is paid to the theory of weak Langmuir turbulence in plasmas with inhomogeneous density. The spectra of one-dimensional parametric turbulence in planar plasmas are considered. It is shown that the inhomogeneity of the density extends the domain of the applicability of weak turbulence theory due to the transfer of the Langmuir wave energy from the region of the excitation of waves to the more rarefield plasma layers. The accelaration of electrons in parametrically turbulent inhomogenous plasmas is discussed. It is shown, that the estimates of the efficiency of parametric energy absorption in plasmas can be obtained not only in the framework of the kinetic theory of waves but also on the basis of the simpler considerationsof the balance of the wave energy fluxes. Estimates of the efficiency of parametric absorption in laser-produced plasmas are given. It is shown that it is possible to have a considerable parametric absorption rate even in the case of steep density gradients. Parametric instabilities can also produce effective absorption in the case of lower-hybrid and electron-cyclotron heating of a plasma in a strong magnetic field.