International EMMI Workshop on Plasma Physics at FAIR, GSI Darmstadt, June 21 - 23, 2017

A precise knowledge of ionization at given temperature and density is required to accurately model compressibility and heat capacity of materials at extreme conditions. We have developed an experimental platform for x-ray Thomson scattering (XRTS) measurements at the National Ignition Facility [1-3] to characterize the plasma conditions in plastic and beryllium capsules in implosion experiments near stagnation. Recently, we have demonstrated XRTS measurements from capsules that were compressed to 30 g/cm3 and inferred electron densities approaching 1025 cm-3, corresponding to a Fermi energy of 170 eV and pressures exceeding 1 Gbar. We will discuss recent results, which show significantly higher ionization than predicted by widely-used ionization models like Stewart & Pyatt. * This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.