Simulations of Anomalous Stimulated Raman Backscattering in a Bounded Plasma

Temporal pulsations, bursting and incoherence of stimulated Raman backscatter in a bounded, underdense plasma were observed in relativistic particle-in-cell simulations. We show that backscatter complexities, modulated and broadened spectra, follow a quasi-periodic and intermittent route to turbulence. We attribute a blue shift to relativistic decrease of plasma frequency. The bursting follows wave breaking, related to hot tail acceleration and bulk heating that further suppress Raman instability. Consistency with short-pulse experiments and simulations at high intensities is outlined.