Nonlinear Models for Coupling the Effects of Stimulated Raman Scattering to Inertial Confinement Fusion Codes

Laser plasma instabilities reduce driver-target coupling and are fundamental limiters of fusion performance for inertial confinement fusion (ICF). Being able to predict and model LPI effects is important for the success of ICF. We present VPIC particle-in-cell simulations of multi-speckled laser beams undergoing stimulated Raman scattering (SRS) at various densities and intensities relevant to indirectly-driven ICF systems. Based on the wavenumber of the SRS daughter electron plasma wave, regions with underpinning SRS saturation physics are identified: Electron-trapping dominated region with intermediate kl_D values, strong damping region at larger kl_D values, and region with the presence of Langmuir decay instability at lower kl_D values. We developed a nonlinear SRS reflectivity model that reflects the base scaling (kl_D)^-4 and its modifications. Electron trapping manifests in the electron distribution functions, and we have developed a new ????-Gaussian-mixture algorithm enabling an accurate characterization of the trapped particle population. Together with this SRS hot electron description, VPIC simulations are used to develop a nonlinear energy deposition model and a hot electron source model based on the Manley-Rowe relations to couple SRS effects to a high-fidelity electromagnetic ICF design code.



* This work was supported by the Los Alamos National Laboratory Directed Research and Development (LDRD) Program. VPIC simulations were run on LANL Institutional Computing Clusters.