Hydrodynamic and atomistic studies in support of high power laser experiments for metal ejecta recollection and interactions (original) (raw)

Ballistic properties of ejecta from a laser shock-loaded groove: SPH versus experiments

The interaction of a shock wave with a rough free surface may lead to the ejection of high velocity (~ km/s) particles of small size (~ µm). This process is a safety issue for various applications such as pyrotechnics or inertial confinement fusion. To complement data obtained by other groups under explosive loading or plate impacts, we use laser driven shock loading to study microjetting from V-shaped grooves of various angles in copper and tin samples, with a combination of complementary experimental techniques. To simulate such experiments, we have chosen to use the Smoothed Particles Hydrodynamics formulation, well-suited for the very high strains involved in jet expansion and subsequent fragmentation. In this paper, we report some advances in this modelling effort, then we compare computed predictions with new experimental results including fragments size distributions inferred from post-test microtomography after soft recovery in a low density gel. Special focus is made on the dependence of the ejecta ballistic properties (velocity and mass distributions) on numerical parameters such as the initial inter-particular distance, the smoothing length and a random geometrical noise introduced to simulate inner irregularities of the material. Shock Compression of Condensed Matter -2017 AIP Conf. Proc. 1979, 080012-1-080012-5; https://doi.

Ejection of spalled layers from laser shock-loaded metals

2010

Dynamic fragmentation of shock-loaded metals is an issue of considerable importance for both basic science and a variety of technological applications, such as inertial confinement fusion, which involves high energy laser irradiation of thin metallic shells. In this context, we present an experimental and numerical study of debris ejection in laser shock-loaded metallic targets ͑aluminum, gold, and iron͒ where fragmentation is mainly governed by spall fracture occurring upon tensile loading due to wave interactions inside the sample. Experimental results consist of time-resolved velocity measurements, transverse optical shadowgraphy of ejected debris, and postshock observations of targets and fragments recovered within a transparent gel of low density. They are compared to numerical computations performed with a hydrodynamic code. A correct overall consistency is obtained.

Spallation and microjetting in laser-shock-loaded aluminium and gold

DYMAT 2009 - 9th International Conferences on the Mechanical and Physical Behaviour of Materials under Dynamic Loading, 2009

Dynamic fragmentation of shock-loaded metals is an issue of considerable importance for both basic science and a variety of technological applications, such as inertial confinement fusion, which involves high energy laser irradiation of thin metallic shells. In this context, we present an experimental and numerical study of fragmentation and debris ejection in laser shock-loaded aluminium and gold, under both nanosecond and sub-picosecond laser pulses. Such fragmentation is mainly governed by two distinct processes: microjetting, that is ejection of thin jets upon shock breakout at the (rough) free surface, and spall fracture, which occurs upon tensile loading due to wave interactions inside the sample. Experimental results consist of time-resolved velocity measurements, transverse optical shadowgraphy of ejected debris, and post-shock observations of recovered targets. They are compared to numerical computations performed with two hydrocodes, and a correct overall consistency is obtained.

Velocity and mass density of the ejecta produced from sinusoidal grooves in laser shock-loaded tin

Journal of Applied Physics, 2020

When a shock wave of several tens of GPa breaks out at a free surface, material is ejected ahead of this surface. The amount and velocity of such ejecta depend on the breakout pressure, state of the released material (solid, liquid, or mixed), whether the shockwave is supported or unsupported and the initial geometrical perturbation (or roughness) of the free surface. If surface defects consist of small grooves, pits or scratches, material ejection occurs in the form of jets breaking up into tiny particles (so-called microjetting), with jet tip velocities up to several times higher than the free surface velocity. The laser-based experiments presented in this paper focus on microjetting in shock-melted tin with periodic surface perturbations. Several complementary diagnostics are combined to measure the velocity and mass of ejecta during the early stages of the jetting process. One relevant advancement is the use of ps-laser X-ray radiography to probe the density of the ejecta in distinct jets a few tens of µm-wide. The effects of the depth and wavelength of the initial perturbation are investigated in both linear and near-linear growth regimes. The results are compared with predictions derived from the Richtmyer-Meshkov Instability (RMI) theory.

Ejection of Micron-Scale Fragments from Triangular Grooves in Laser Shock-Loaded Copper Samples

Journal of Dynamic Behavior of Materials, 2016

When a material is submitted to a dynamic compression, a shock wave propagates through the bulk and potentially interacts with a free surface. If this surface has geometrical defects such as grooves, some material ejection can occur. The energy of the high velocity ejecta is an area of concern for many applications, such as industrial safety, pyrotechnics or inertial confinement fusion. We have studied this phenomenon of microjetting from calibrated grooves in laser shock-loaded Cu samples, combining complementary experimental, numerical and analytical approaches, in order to investigate the formation and the fragmentation of the jets over ranges of small spatial (*lm) and temporal (*ns) scales and extremely high strain rates (*10 7 s-1). Various grooves were used with different depths and aperture halfangles (20°, 30°, 45°). The velocities measured by fast shadowgraphy and heterodyne velocimetry were compared to numerical predictions using the finite element or the smoothed particles hydrodynamics formulations with the Radioss code. Size distribution of the ejecta was inferred from rough measurements of the debris sizes and compared to analytical predictions from a probability law.

Material ejection from surface defects in laser shock-loaded metallic foils

SHOCK COMPRESSION OF CONDENSED MATTER - 2019: Proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter

Ejecta production upon the breakout of a shock wave at a rough surface has been the subject of extensive research work for about six decades. For a few years, we have investigated how laser-driven shocks could provide original, complementary data on this issue, over specific ranges of very high loading pressures, very short pulse durations (ns-order), small dimensions (tens of µm) and extremely high strain rates. Here, selected results are presented in two metals (Cu and Sn), with either single triangular grooves of controlled depths and sharp angles or periodic, quasi-sinusoidal perturbations of different amplitudes. Experimental data combine measurements of jet velocities, using both optical shadowgraphy and Photonic Doppler Velocimetry, with ultra-fast laser based X-ray radiography to estimate mass ejection. Results are briefly compared with the predictions of analytical models and data obtained by other teams from explosive-based experiments, at lower pressure and over much larger temporal and spatial scales. Thus, both interest and limitations of laser shocks for this particular field of shock physics are illustrated and discussed.

Shock-hydrodynamics experiments on the Nova laser

1995

Abstract: We have conducted shock-induced hydrodynamics experiments using the Nova laser at Lawrence Livermore National Laboratory. The laser provides a highenthalpy source by depositing its energy (about 22 kj) in a small gold cavity called a Hohlraum. The ...

Particle-in-cell Simulations on Laser-Plasma Interactions in Shock Ignition

Bulletin of the American Physical Society, 2012

We present a series of 1D and 2D particle-in-cell (PIC) simulations using the full PIC code\ textit {OSIRIS} for the shock ignition experiments carried out on the OMEGA facility. The laser intensity is $ I= 2\ times 10^{15} /cm/cm /cm^ 2$. The density profile used in PIC simulations is provided by the hydro simulation and has the scale length $ L= 17\ mu $ m at the quarter-critical-density surface. Physical electron-ion collisions are included in our simulations with a benchmarked collision package in\ textit {OSIRIS}. The 1D simulation covering a larger ...

The study of high-speed surface dynamics using a pulsed proton beam

2012

We present experimental results supporting physics based ejecta model development, where we assume ejecta form as a special limiting case of a Richtmyer-Meshkov (RM) instability with Atwood number A = −1. We present and use data to test established RM spike and bubble growth rate theory through application of modern laser Doppler velocimetry techniques applied in a novel manner to coincidentally measure bubble and spike velocities from shocked metals. We also explore the link of ejecta formation from a solid material to its plastic flow stress at high-strain rates (10 7 /s) and high strains (700%).