Proton radiography measurements of ejecta structure in shocked Sn*

We have performed ejecta measurements at the Los Alamos proton radiography facility on 7 mm thick 50 mm diameter Sn samples driven with a PBX9501 high explosive. The surface of the Sn, in contact with He gas at an initial pressure of 7 atmospheres, was machined to have 3 concentric sinusoidal features with a wavelength of $\lambda =$2mm in the radial direction and amplitude h$_{0}=$0.159mm (kh$_{0}=$2$\pi $h$_{0}$/$\lambda =$0.5). The shock pressure was 27 GPa. 28 images were obtained between 0 and 14 $\mu $s from the time of shock breakout at 500 ns intervals. The Abel inverted density profiles evolve to a self-similar density distribution that depends on a scaling variable z/v$_{s}$t where v$_{s}$ is the spike tip velocity, z is the distance from the free surface and t is the time after shock breakout. Both the density profiles and the time dependence of the mass per unit area in the evolving spikes are in good agreement with a Richtmyer-Meshkov instability based model for ejecta production and evolution.