Fluid modeling of stimulated Raman scattering accounting for trapped particles benchmarked against fully kinetic simulations

Abstract

A new fluid model describing backward stimulated Raman scattering (SRS) is presented based on parametric three-wave coupling in multidimensional geometry. It takes into account kinetic effects in the description of the plasma wave via a nonlinear frequency shift due to trapped electrons. This model is valid in the regime of hot and weakly inhomogeneous plasmas under conditions relevant for inertial confinement fusion with the plasma parameter $k_L{\lambda }_{De}⩾$ 0.25 (where k_L stands for the plasma wave number and λ_De for the Debye length). Benchmarks of the model have been performed against the Maxwell-particle-in-cell (PIC) code Emi2D in order to calibrate the adjustable parameters controlling the nonlinear frequency shift. Two major configurations have been tested, one in a homogeneous plasma, with the onset of laser pump depletion, and the other in an inhomogeneous plasma, producing auto-resonant growth. Good agreement between fluid and PIC simulations has been found for both configurations, in particular, for the growth of SRS, and further on in time for the average backscatter level. This model is a promising tool to be implemented in multi-dimensional laser-plasma interaction packages coupled to hydrodynamics codes in order to compute SRS in mm-size volumes, usually inaccessible with PIC codes.