Simulations of laser-driven metal ejecta

When a shockwave travels through a metal sample and reaches a structural defect such as a pit or a groove at the surface, materials may be ejected as clouds of small particles or directed microjets. Understanding how such ejecta form and propagate has important implications for a wide range of applications, from the design of spacecraft shielding to the study of planetary impacts.

Mackay et al. performed high-resolution hydrodynamic simulations to study the phenomenon. The effort is part of the Metal Ejecta: Recollection, Interaction, and Transport (MERIT) project at Lawrence Livermore National Lab. The computational analysis demonstrates that the choice of material models can have a strong influence on microjet formation and evolution, depending on drive strength.

The authors used a radiation hydrodynamics code to simulate laser-driven microjets from micron-scale grooves on a tin surface. They investigated how two different equation of state models for tin affect the simulated microjet formation and propagation across a range of drive strength.

They found that, in the weakly-driven regime, material strength limits material ejection. In the moderately-driven regime, localized melting causes a jump in the mass of the microjet, and the choice of material model strongly affects the free surface velocity. In the strongly-driven regime, a larger amount of material is melted, but the mass of the microjet does not change, and results are insensitive to the material model.

In terms of future work, the authors plan to simulate how multiple microjets interact with one another and how those interactions affect free surfaces. The combination of computational models and experimental data from MERIT will provide insight into the quality of ejecta-ejecta and ejecta-surface interactions.

Source: “Hydrodynamic computations of high-power laser drives generating metal ejecta jets from surface grooves,” by K. K. Mackay, F. M. Najjar, S. J. Ali, J. H. Eggert, T. Haxhimali, B. E. Morgan, H. S. Park, Y. Ping, H. G. Rinderknecht, C. V. Stan, and A. M. Saunders, Journal of Applied Physics (2020). The article can be accessed at http://doi.org/10.1063/5.0028147 .