Comparison of absolute Hugoniots in structured and unstructured CH foams*

Many advanced ICF target designs utilize low density CH to increase ablation velocity and reduce instability growth. As such, precise determination of the CH foam Hugoniots is important for target design and modeling. Shocks driven at foam densities (50 to 150 mg/cm3) and Mbar pressures require piston velocities above the limits of explosively driven experiments, necessitating laser drivers. The Nike laser has been utilized to perform absolute Hugoniot measurements using structured (2PP) and unstructured (DvB) foams with

characteristic sizes varying from 1 to 50 μm. Nike produces shock pressures up to 9 Mbar with a highly uniform, time averaged, 400 μm flat-top beam profile, providing a unique platform for low-density equation-of-state experiments. Measurements were made using a high resolution monochromatic x-ray streaked imager which allowed independent measurement of the shock and piston velocities. Our experiments covered the shocked particle velocity range from 25 to 90 km/s and included inflight control of steadiness of the measured shock and piston velocities over the shock travel distance 400 μm. Comparisons are made between the various experimental results as well as numerical simulations using CALEOS in the NRL FASTRAD3D hydrocode. Work supported by US DoE/NNSA.