Observation of ejecta tin particles into polymer foam through high-energy X-ray radiograpy using high-intensity short-pulse laser

Abstract

Micron-scale fragment ejection of metal is a kind of surface dynamic fragmentation phenomenon upon shock loading. The study of ejecta is crucial in many fields, such as inertial confinement fusion and pyrotechnics. Due to the particular advantages of laser experiments, a lot of studies of ejecta by strong laser-induced shock loading have been conducted in recent years. The shapes, size and mass of particle can be obtained via static soft recovery technique with foam. However, the stagnation and succedent mixing of the ejecta in the foam could not be deduced by this technique. To study the mixing between the ejecta and foam, a radiography experiment is performed by using the X-ray generated through the irradiation of picosecond laser on the golden wire. This radiography technique has not only high spatial resolution but also high temporal resolution. Two kind of experiments are designed and performed. In the first one, the tin sample and the foam are close to each other while a vacuum gap is arranged between them in the other one. The mixing process is analyzed with the determined areal density and volume density, as well as the results of recovery. The areal density of the front mixing area is similar to the scenario in the case with a vacuum gap, suggesting that the ejecta have not underwent a secondary fragmentation due to the collision with foam. Furthermore, the static recovery results show a different characteristic of penetration depth for the ejecta in the foam. When the tin sample is not close to the foam, the penetration depth in the foam increases with the loading pressure increasing. However, the penetration depth begins to decrease at a critical pressure after a brief increase, which is attributed to the interaction between the shock and the foam before the ejecta coming, and also to the ejecta size and composition. The shock pressure is high enough to change the foam performance, thus enhancing the stagnation ability for ejecta penetration. Moreover, the size and composition vary with loading pressure, thereby leading to the momentum change of the ejecta related to the penetration depth. In the future work, we will improve the field of view of the X-ray radiography to achieve a direct comparison between the dynamic results and the recovery results. Moreover, we will arrange perturbations at the interface to study the mixing between the micro-jetting and the foam and the interface instability.