Relaxation of a parametric turbulence in a plasma

A theoretical (analytic and numerical) study is made of a nonstationary (transient) plasma turbulence initiated by a parametric instability involving decay of a pump wave into two plasmons and saturated by the stimulated scattering of plasmons on ions. The main features of the relaxation of such a parametric turbulence are governed by the characteristics of the noise saturation mechanism and are in this sense typical of many other instabilities which can be stabilized by stimulated scattering. A solution of a nonlinear integro-differential equation for the spectral density of the noise energy reveals the complete evolution pattern of the appearance and growth of a turbulent noise, which oscillates in time, has a modulated spectrum, and finally attains a smooth stationary (steady-state) distribution. A nonstationary parametric turbulence can develop fully in a dense laser plasma during a nanosecond pulse emitted by a high-power neodymium laser.