Atomistic Dynamics of the Richtmyer-Meshkov Instability in Cylindrical and Planar Geometries

We apply molecular dynamics (MD) simulations to study the evolution of the shock-driven Richtmyer-Meshkov instability (RMI) in the cylindrical and planar geometries. Compared to traditional hydrodynamic simulations, MD has a number of fundamental advantages: it accounts for strong gradients of the pressure and temperature, and captures accurately the heat and mass transfers at the early stage (shock passage) as well as the late stage (perturbation growth) of the instability evolution. MD has no hydrodynamic limitations for spatial resolution and thermodynamic quasi-equilibrium at atomic scale. We study the instability evolution for different perturbation modes and analyze the role of the vorticity production for RMI dynamics

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. The development of the diagnostic methods for the subpicosecond timescale was of exceptional importance. With these methods, not only the generation, but also the measurement of fast pro cesses initiated by a femtosecond laser became possi ble. The initiation and measurements are performed with a pair of ultrashort pulses using the stroboscope principle Femtosecond lasers are very efficient generators of shock waves in a condensed phase. They are used together with the pump-probe measurement method Interesting results on the superelastic behavior of a crystal under ultrashort shock compression were obtained in The results on superelasticit

Spallative ablation of dielectrics by X-ray laser

Short laser pulse in wide range of wavelengths, from infrared to X-ray, disturbs electron-ion equilibrium and rises pressure in a heated layer. The case where pulse duration $\tau_L$ is shorter than acoustic relaxation time $t_s$ is considered in the paper. It is shown that this short pulse may cause thermomechanical phenomena such as spallative ablation regardless to wavelength. While the physics of electron-ion relaxation on wavelength and various electron spectra of substances: there are spectra with an energy gap in semiconductors and dielectrics opposed to gapless continuous spectra in metals. The paper describes entire sequence of thermomechanical processes from expansion, nucleation, foaming, and nanostructuring to spallation with particular attention to spallation by X-ray pulse

Molecular Dynamics Simulations of the Richtmyer-Meshkov Instability in Shock Loaded Solids

For the first time, molecular dynamics simulations (MD) are applied to study the evolution of shock-driven Richtmyer-Meshkov instability of the perturbations at a solid surface and at the interface separating two solids of different densities. We study the dependence of the instability evolution on the strength and orientation of the shock, and analyze the structure of the material in a vicinity of the interface perturbations (i.e. the spikes and bubbles)