Iron Equation of State Measurements on the Z-Machine

We have measured the equation of state of iron along an elevated quasi-isentrope from 275 GPa to 400 GPa, reaching pressure and temperature conditions similar to the core of the Earth. This is enabled by the shock-ramp capability at Sandia National Laboratory's Z machine, a pulsed power facility which can probe off-Hugoniot P-T regions by shocking a material and subsequently driving a further shockless compression. The resulting unique parameter space is lower in temperature than a shock Hugoniot, but higher than the primary isentrope. We derive the EOS using an iterative backward integration -- forward Lagrangian technique on particle velocity traces from symmetrically-loaded sample pairs of differing thicknesses. Sandia National Labs is managed and operated by National Technology {\&} Engineering Solutions of Sandia, LLC, a subsidiary of Honeywell International, Inc., for the U.S Dept. of Energy's National Nuclear Security Administration under contract DE-NA0003525. SAND2019-1631 A