Using the Colliding Planar Shocks Platform at the National Ignition Facility for measuring the opacity of dense carbon plasmas*

Opacity measurements in dense carbon plasmas play a vital role for understanding the radiative transfer, energy transport, and equation of state (EOS) of imploding inertial confinement fusion (ICF) capsules as well as many astrophysical phenomena. Widely used ionization models appear to underpredict ionization and thus overpredict opacity at high density conditions, even for low-Z materials. Accurate understanding of both the ionization and opacity of highly compressed carbon is crucial for improving predictive capabilities in high energy density (HED) applications including ICF and stockpile stewardship. Here we present an innovative experimental approach utilizing the Colliding Planar Shocks (CPS) platform [1] at the National Ignition Facility (NIF) for measuring the opacity of carbon at conditions where the K-shell is expected to ionize. Recent experiments using the CPS platform have demonstrated large volumes of highly compressed matter with minimal spatial gradients to make high precision measurements of materials under extreme conditions. Key variables such as the electron temperatures, electron densities, and ionization states can be extracted using simultaneous X-ray Thomson scattering (XRTS) and X-ray radiography. Initial experiments using the CPS platform have recently demonstrated the ability to compress solid CH and CH foams 3–8 times solid densities, as well as reach electron temperatures between 10-50 eV, and material pressures of 30–100 Mbar.