Modeling stimulated Raman scattering in multidimensional configurations for ICF

Inertial Confinement Fusion is one of the two major ways to achieve thermonuclear fusion of light nuclei in laboratory. The thermonuclear reactions are initiated with mega-joule-class lasers, using the direct or the indirect drive scheme. Our main concern is the indirect drive scheme, where laser beams propagate through a hot and under-dense plasma in which they undergo substantial losses, because of laser-plasma instabilities. These losses are highly detrimental in the sense that they reduce the laser energy deposition needed to eventually compress the fuel via inertial confinement. More precisely, the incident laser light can be reflected in scattering processes, one of which is the Stimulated Raman Scattering (SRS) off electron plasma waves, leading to substantial energy losses (up to 50%). Although this instability has been investigated for many years, its modeling remains difficult particularly for millimeter-size and inhomogeneous plasmas in long time scales (nanosecond). One major difficulty is the quick evolution toward nonlinear regimes related to the important modification of the electron distribution function. The challenging goal of this work is to develop a realistic model for SRS in ICF relevant plasmas, on long time scale, taking into consideration the different nonlinear effects associated with electron plasma waves. A new wave coupling approach, implemented in a 2D/3D code, was elaborated and successfully confronted with reference kinetic simulations from a PIC code. Ultimately, the developed model is applied to recent experimental contexts and allows a novel and relevant interpretation of some measurements. (author)