Experimental Investigation of a Direct-Drive Shock Wave Heated and Compressed Planar Target relevant to ICF

An experimental investigation of shock wave induced heating and compression in planar targets relevant to direct-drive inertial confinement fusion (ICF) was conducted on the OMEGA laser system. A physical understanding of shock wave heating, radiative heating, and heating by energetic electrons in direct-drive ICF is necessary because the achievement of energy gain requires accurate control of the pressure in the main fuel layer. The shock wave provides the dominant heating mechanism. Plasma conditions of a direct-drive shock wave heated and compressed planar plastic target were diagnosed using non-collective, spectrally resolved x-ray scattering and time-resolved x-ray absorption spectroscopy. In the non-collective x-ray scattering experiment, the spatially averaged electron temperature (Te) and average ionization (Z) of the shock wave heated target were inferred from the spectral line shape of the Rayleigh (elastic) and Compton (inelastic) components. Local plasma conditions during shock wave heating and compression as well as the timing of heat front penetration were diagnosed with time-resolved Al 1s-2p absorption spectroscopy of planar plastic foils with a buried layer of Al. The measured Al 1s-2p spectra were analyzed with an atomic physics code PrismSPECT to infer Te and the mass density (ρ) assuming uniform plasma conditions. The experimental results for a variety of square and shaped laser pulse drives were compared with the 1-D hydrodynamics code LILAC using a flux-limited (f = 0.06 and f = 0.1) and a nonlocal thermal transport model. The accuracy of the electron temperatures inferred from the absorption spectroscopy experiment was sufficient to validate the electron thermal transport model in LILAC. The LILAC simulation using the nonlocal model or f = 0.06 accurately