Parametric decay in an inhomogeneous plasma

It is shown, with parametric transformation of a pumping wave to a Langmuir and ion-sound waves serving as an example, that an absolute instability due to the spatial structure of the pumping wave may develop in an inhomogeneous plasma. In the case of such an instability disturbances whose amplitudes increase with time are localized near extrema of the pumping wave field. It is also shown that disturbances of two types occur in plasma, whose excitation thresholds have been determined. Under conditions of interest for achieving a controlled thermonuclear reaction by laser radiation of solid targets the instability threshold is determined substantially by a plasma inhomogeneity and surpasses by far the threshold in a homogeneous plasma. The effect of absorption of the pumping wave on parametric decay has been examined