R A D I O G R A P H Y

Direct Density Measurements of Multi-Mbar Shock Waves for Absolute Equation-of-State Studies

At high-energy-density conditions, laser-driven shock-wave studies have typically determined the Hugoniot of a material by impedance-matching to a known standard; however, the need to perform experiments at high pressures (>5 Mbar), where uncertainties in the EOS of the standard material (such as Aluminum) become significant, ultimately limit the utility of such a relative EOS technique.

Previous efforts to perform absolute EOS measurements using time-resolved x-ray radiography were limited by the extreme precision required to measure shock and particle velocities at such high compressions. We are performing experiments on the OMEGA laser system that employ a new technique designed to achieve direct density measurements in a shock wave.

Side-on radiography using point-projection imaging (@~5-keV) is used to produce a snapshot of the expanding shock wave; this 2-D image is then tomographically inverted to determine the density profile behind the shock front. By simultaneously measuring the shock velocity using VISAR, absolute equation-of-state points are determined. This technique conveniently scales to measurements on higher-Z materials using harder x-rays from an intense short pulse laser.

UCRL-WEB-221357