Cylindrical Driven Shocks in Ceria*

Shock compression of granular ceria was studied in converging cylindrical geometry using LANL Proton Radiography driven by the PHELIX magnetic implosion system in which a 1 mm thick liner-impactor was accelerated it to ~0.8 mm/$\mu s$. The impactor launched a shock in the cylindrical Al outer wall of the target assembly containing equiaxed, 63 $\mu$m-mean diameter ceria powder initially compacted to a static density of ~4 g/cc. The cylindrically converging shock in the ceria was observed with a series of 31 proton-radiographic frames down the axis of the cylinder. Results indicate that significant shock energy was expended in compacting the porous ceria, as the wave velocity markedly decreases during convergence, and a clear shock reflected from the axis was not observed. These observations are inconsistent with pre-shot modeling, and highlight the need for an improved understanding of the physics of compaction under non-ideal loading.