Probing the Evolution of Solid Microjets From Grooved Tin Sample Using X-Ray Radiography: Evidence of Coalescence Edge Effects

Abstract The reflection of a shock wave at the interface between the free surface of metallic sample presenting geometrical defects and air can lead to the ejection of a great amount of micron-scale particles, called ejecta. Indeed, the defects, such as pits, scratches, or grooves, form thin jets that expand ahead of the main surface and then break into small particles. This process, which is referred to as microjetting, is a major safety issue in shock-related work, such as pyrothechnics or inertial confinement fusion (ICF) where it can disrupt measurements, damage nearby equipment or even represents safety hazards. The comprehensive understanding of this process is thus of crucial importance. Although this phenomenon has been studied for long, several points are still not fully understood, in particular the influence of edge effects. Here, we use X-ray radiography to image the evolution of solid microjets from grooved Sn samples. Jet generation was obtained through the impact of a high-speed copper projectile launched with a gas gun on the sample. Several groove geometries (chevron, fly-cut and square profiles) have been compared. An edge effect often reported, but not understood, is the increased density of the jets at the interface of grooved and plain surfaces. Here we clearly demonstrate that this is due to a lateral deformation in the generation of the border jet, leading to its coalescence with its adjacent neighbor.