Growth of stimulated Raman instability by a density-modulated electron beam in laser-plasma interactions

Abstract

A way to enhance the growth of stimulated Raman instability in laser-plasma interactions was investigated. This relies on the application of density modulation of a co-propagating electron beam in plasmas. In the stimulated Raman scattering process, an electromagnetic pump wave decays into a low-frequency wave and a scattered electromagnetic sideband wave. In this process, the pump wave produces an oscillatory velocity associated with the plasma electrons and the beam electrons. These oscillatory velocities combine with the existing low-frequency mode, producing ponderomotive force that drives high-frequency sideband waves. The sidebands couple to the pump wave, driving the beam-mode. A modulation of the electron beam density enhances the growth rate of the instability. The theoretical calculations show about 40% enhancements in growth of Raman instability at resonance (where the electron beam density modulation parameter approaches to unity) for the plasma density of the order of 1018 cm−3.