TRANSVERSE SHADOWGRAPHY AND NEW RECOVERY TECHNIQUE TO INVESTIGATE DYNAMIC FRAGMENTATION OF LASER SHOCK-LOADED METALS

With the development of high energy laser facilities dedicated to inertial confinement fusion, the question of debris ejection from metallic shells subjected to intense laser irradiation has become a key issue. We have used two diagnostics to investigate this phenomenon. Transverse shadowgraphy is an optical time-resolved diagnostic. It provides successive images that allow characterizing the motion of fragments generated by processes such as microjetting and spallation. Quasi-instantaneous pictures of the debris clouds are obtained and mean ejection velocities can be derived. Complementary data are provided by post-shock analysis of recovered fragments. Such recovery can be achieved in aerogels, but their brittleness and low transparency make the analysis difficult. Instead, we have used a new technique, based on a highly transparent gel of density 0.9 g/cm(3), which allows soft recovery and easy observation of the fragments sizes, shapes and penetration depths, with a spatial resolution of pm-order.