The competition between forward stimulated Raman side-scattering (FSRSS) and backward stimulated Raman side-scattering (BSRSS) is investigated under Ignition-scale conditions using particle-in-cell (PIC) simulations. Experimental observations at the National Ignition Facility (NIF) have demonstrated the significance of stimulated Raman side-scattering or backscattering instability compared to two-plasmon-decay (TPD) under ignition-scale conditions for various laser beam geometries. Since side scatter requires the scattered light perpendicular to the density gradient, in the cases of oblique incidence, the scattered light can project either backward or forward relative to the incident beam. Under Ignition-scale conditions, linear analysis shows that both BSRSS and FSRSS are absolute (temporally growing) at higher densities (ne ∼ 0.2nc), whereas at lower densities (ne ∼ 0.1nc), BSRSS becomes convective with a substantial gain, while FSRSS remains absolute. Two-dimensional (2D) PIC simulations demonstrate that the competition between BSRSS and FSRSS is sensitive to the density. BSRSS tends to dominate at higher densities, while FSRSS becomes more dominant at lower densities. At a moderate density (ne ∼ 0.15nc), FSRSS and BSRSS can coexist. Furthermore, an increase of laser intensity leads to enhanced electron trapping, which kinetically strengths and then saturates BSRSS in the lower density region.
 

stimulated Raman sidescattering, hot electrons, kinetic inflation