Coupling of laser energy to converging shocks in direct-drive solid sphere experiments on the NIF

Laser-energy to converging shock, Polar direct drive (PDD)[1] experiments using 2.1-mm diameter solid CH sphere targets have been performed on the National Ignition Facility (NIF). Multiple intensities and pulse shapes are used to validate laser energy-to-target coupling models in 2-D radiation hydrodynamic simulations. Analysis of time resolved scattered light collected at a narrow wavelength band around 351 nm from scattered light time history diagnostics (SLTDs)[2]^,[3] and full aperture backscatter stations (FABS) and x-ray radiography images, used to track shock trajectories, collected from time-gated x-ray detectors (GXD) are used to compare to simulations from 2-D radiation hydrodynamic code DRACO. These comparisons are used to constrain physics models such as the cross-beam energy transfer (CBET), non-local transport, and equation of state (EOS) models. DRACO overpredicts late-time shock velocity and absorbed light at lower intensities but gets into better agreement as laser intensity increases. These trends will be examined to evaluate the models in DRACO.

[1] M. Hohenberger et al., Phys. Plasmas 22, 056308 (2015).

[2] M. J. Rosenberg et al., Rev. Sci. Instrum. 92, 033511 (2021).

[3] S. Kostick et al., Rev. Sci. Instrum. 95, 093524 (2024).