Simulations of coronal plasma hydrodynamics in the laser–plasma interaction experiments at the Laser Mégajoule*

Laser–plasma instabilities can degrade the performance of direct-drive inertial confinement fusion implosions. Stimulated Raman scattering (SRS) is one of the primary concerns because it can generate hot electrons, which prematurely preheat the fuel impeding the compression, and the laser can be scattered away, reducing the energy coupled to the target. We have developed and fielded planar laser–plasma interaction experiments at the Laser Mégajoule to study the SRS mechanisms. Simulations using the radiation-hydrodynamic code DRACO will be presented and demonstrate that direct-drive ignition-relevant plasma conditions have been achieved. The computed plasma profiles have been used for subsequent calculations of the SRS scattered light. Indications of the inner-to-outer quad cross-beam energy transfer have been obtained, which prompted SRS experiments using outer and inner beams separated in time. Time-dependent measurements of SRS over wide angles [V. Trauchessec et al., Rev. Sci. Instrum. 93, 103519 (2022)] provided indirect measurements of the hydrodynamics, which will be compared to the simulations.