Theory of weakly turbulent plasma

Plasma as a many-body system has a large number of degrees of freedom and thus has a wide variety of possible collective motions. When the amplitudes of these collective motions become finite as a result of the appropriate instability development, then nonlinear effects result in the interaction of these motions with each other. The plasma could be considered turbulent in this case. The wide class of kinetic plasma instabilities results in the excitation of the plasma eigenmodes with small amplitudes. The nonlinear interaction of such modes is weak, and this permits them to be considered independent in a first approximation. As a result, an arbitrary disturbance can be represented in the form of an eigenmode expansion. The equations of this theory can be derived from first principles. It is convenient to lay down the theory of weakly turbulent plasma in terms of the three basic types of interaction: quasilinear wave-particle interaction; nonlinear wave-wave interaction; and wave-particle-wave interaction (known as nonlinear wave-particle interaction). (Auth.)