Experimental Observations of Laser-Driven Tin Ejecta Microjet Interactions

The study of high-velocity particle-laden flow interactions is broadly applicable to fields ranging from planetary formation to cloud interaction dynamics. Ejecta microjets offer a novel experimental methodology to study such interactions, as microjets consist of micron-scale particles that travel at velocities greater than several kilometers per second. At such velocities, collisions between particles can cause break-up or conglomeration and can impart enough energy to alter the material state through melting or vaporization. As such, interaction behavior of high-velocity particle flows is difficult to predict and requires experimental data to benchmark collisional models. Ejecta microjets are generated when a strong shock releases from a surface with a feature, such as a groove or a divot; the feature then inverts as a limiting case of the Richtmyer-Meshkov Instability and forms a propagating jet of material. We present on experiments performed at the OMEGA EP laser facility that observed the interaction of two counter-propagating tin ejecta microjets for the first time through x-ray radiography imaging [1]. We observe that jets emerging from a shock pressure of 11.7 GPa pass through each other unattenuated, whereas jets emerging from a shock pressure of 116.0 GPa have five times greater densities and interact strongly, forming a cloud around the center-point of interaction. Radiation hydrodynamics simulations of particle-stream collisions capture many of the observed interaction characteristics but are unable to capture the full spread of the cloud formed, suggesting that more work is needed to understand the physics dominating collisional behavior of ejecta microjets.