Modeling of Two-Plasmon--Decay Experiments at Polar-Direct-Drive Ignition-Relevant Plasma Conditions at the National Ignition Facility

The two-plasmon--decay (TPD) instability can be detrimental for direct-drive inertial confinement fusion because of target preheat by high-energy electrons generated by TPD. The radiation--hydrodynamic code \textit{DRACO} has been used to design planar target experiments that generate plasma and interaction conditions relevant to ignition polar-direct-drive (PDD) designs. The use of planar targets allows TPD to be decoupled from cross-beam energy transfer, which reduces the laser absorption in current National Ignition Facility (NIF) PDD implosion experiments. The laser--plasma interaction code \textit{LPSE} has been used to investigate TPD using the predicted plasma profiles and laser irradiation geometry in three dimensions. The energetic electrons generated by \textit{LPSE } are propagated into the planar target using the Monte Carlo transport code \textit{EGSnrc.} This enables a direct comparison between the simulated and experimentally observed Mo K$_{\alpha }$ fluorescence and hard x-ray bremsstrahlung. The plasma profiles have been post-processed for stimulated Raman and Brillouin backscatter gains. Comparisons of these results with recent experiments at the NIF and the implications for ignition-scale PDD experiments will be presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.