High-Precision Hugoniot measurements for CH foams in the 2-9 Mbar range

Absolute Hugoniot measurements for plastic foams at ~10% of solid CH density and supporting simulation results are reported. Planar foam slabs, ~400 μm thick and ~500 μm wide, some of which were covered with a 10 μm solid plastic ablator, were directly driven with 4 ns long Nike KrF 248 nm wavelength laser pulses that produced strong shock waves in the foam. The shock and mass velocities in our experiments were up to 104 km/s and 84 km/s, respectively, and the shock pressures up to ~9 Mbar. The motion of the shock and ablation fronts was recorded using side-on monochromatic x-ray imaging radiography. The steadiness of the observed shock and ablation fronts within ~1% has been verified. The Hugoniot data inferred from our velocity measurements agree with the predictions of the EOS models, such as SESAME, near the highest pressure ~9 Mbar, but from 2 to 5 Mbar, a lower shock density compression is observed than that predicted by the models. Possible causes for this discrepancy are discussed.