The study of high-speed surface dynamics using a pulsed proton beam (original) (raw)
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Unstable Richtmyer–Meshkov growth of solid and liquid metals in vacuum
Journal of Fluid Mechanics, 2012
We present experimental results supporting physics based ejecta model development, where our main assumption is that ejecta form as a special limiting case of a Richtmyer-Meshkov (RM) instability at a metal-vacuum interface. From this assumption, we test established theory of unstable spike and bubble growth rates, rates that link to the wavelength and amplitudes of surface perturbations. We evaluate the rate theory through novel application of modern laser Doppler velocimetry (LDV) techniques, where we coincidentally measure bubble and spike velocities from explosively shocked solid and liquid metals with a single LDV probe. We also explore the relationship of ejecta formation from a solid material to the plastic flow stress it experiences at high-strain rates (10 7 /s) and high strains (700%) as the fundamental link to the onset of ejecta formation. Our experimental observations allow us to approximate the strength of Cu at high strains and strain rates, revealing a unique diagnostic method for use at these extreme conditions. SB ( * see Appendix A for a glossary of relevant shockwave physics terms). Those measurements can then be integrated into a hydrodynamic code that adds the measured source † Email address for correspondence: buttler@lanl.gov
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.
SHOCK COMPRESSION OF CONDENSED MATTER - 2019: Proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter
Shock-driven material can emit a fine spray of ejecta from its free surface. Understanding the dynamic and interaction of the metal ejecta is important to areas of study as diverse as industrial safety, astrophysics, spacecraft shielding, additive manufacturing and inertial confinement fusion. In this work we present results from hydrodynamic simulation studies in support of designing experiments on the OMEGA and OMEGA-EP laser platforms. The initial experimental campaign was focused on developing a platform aimed at launching hypervelocity particles. We have used a finite element formulation with ALE3D (Arbitrary Lagragian Eulerian) code in support of this campaign. Fields like pressure and velocity of elements produced in the ablated part of material are computed using the FLASH radiation-hydrodynamic code. These are then used as input in a "handshaking" region ALE code to capture shock propagation and the dynamics of the particles. As the campaign has shifted towards producing the ejecta and studying its interaction we have also undertaken an atomistic study to reveal at the ab-initio level the physics of the formation of ejecta when grooves are present in the free surface. This will be included as a framework in a multiscale study relating atomistic with the hydrodynamic scale formation of the ejecta.
Tracking ultrafast dynamics of intense shock generation and breakout at target rear
Physics of Plasmas, 2018
We report upon the picosecond plasma dynamics at the rear surface of a thin aluminium foil (of either 5.5 µm or 12µm thickness) excited by high contrast (picosecond intensity contrast of 10 −10), 800 nm, femtosecond pulses at an intensity of 3 × 10 19 W/cm 2. We employ ultrafast pump-probe reflectometry using a second harmonic probe (400 nm) interacting with the rear surface of the target. A rise in the probe reflectivity 30 picoseconds after the pump pulse interaction reveals the breakout of a shock wave at the target rear surface which reflects the 400 nm probe pulse. Simulations using the ZEPHYROS hybrid particle-in-cell code were performed to understand the heating of the target under the influence of the high intensity laser pulse, and the temperature profile was then passed to the radiation-hydrodynamics simulation code HYADES in order to model the shock wave propagation in the target. A good agreement was found between the calculations and experimental results.
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.
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.
EPL (Europhysics Letters), 2017
Laser-plasma interaction (LPI) at intensities 10 15-10 16 W • cm −2 is dominated by parametric instabilities which can be responsible for a significant amount of non-collisional absorption and generate large fluxes of high-energy nonthermal electrons. Such a regime is of paramount importance for inertial confinement fusion (ICF) and in particular for the shock ignition scheme. In this paper we report on an experiment carried out at the Prague Asterix Laser System (PALS) facility to investigate the extent and time history of stimulated Raman scattering (SRS) and two-plasmon decay (TPD) instabilities, driven by the interaction of an infrared laser pulse at an intensity ∼1.2 × 10 16 W • cm −2 with a ∼100 µm scalelength plasma produced from irradiation of a flat plastic target. The laser pulse duration (300 ps) and the high value of plasma temperature (∼4 keV) expected from hydrodynamic simulations make these results interesting for a deeper understanding of LPI in shock ignition conditions. Experimental results show that absolute TPD/SRS, driven at a quarter of the critical density, and convective SRS, driven at lower plasma densities, are well separated in time, with absolute instabilities driven at early times of interaction and convective backward SRS emerging at the laser peak and persisting all over the tail of the pulse. Side-scattering SRS, driven at low plasma densities, is also clearly observed. Experimental results are compared to fully kinetic large-scale, two-dimensional simulations. Particle-in-cell results, beyond reproducing the framework delineated by the experimental measurements, reveal the importance of filamentation instability in ruling the onset of SRS and stimulated Brillouin scattering instabilities and confirm the crucial role of collisionless absorption in the LPI energy balance.
Rayleigh-Taylor Growth with Material Strength
We present experimental results supporting physics-based ejecta model development, where our main assumption is that ejecta form as a special limiting case of a Richtmyer-Meshkov (RM) instability at a metal-vacuum interface. From this assumption, we test established theory of unstable spike and bubble growth rates, rates that link to the wavelength and amplitudes of surface perturbations. We evaluate the rate theory through novel application of modern laser Doppler velocimetry (LDV) techniques, where we coincidentally measure bubble and spike velocities from explosively shocked solid and liquid metals with a single LDV probe. We also explore the relationship of ejecta formation from a solid material to the plastic flow stress it experiences at high-strain rates (10 7 s −1 ) and high strains (700 %) as the fundamental link to the onset of ejecta formation. Our experimental observations allow us to approximate the strength of Cu at high strains and strain rates, revealing a unique diagnostic method for use at these extreme conditions.
Studies on laser driven shocks in Aluminum and Gold targets at >10 Mbar pressure
Journal of Physics: Conference Series, 2010
study of Equation of State (EOS) at high pressures is of interest for several fields of Physics, in particular astrophysics, material science and inertial confinement fusion. The Laser driven shock studies on various targets have been done with the 10 J/ 500 ps laser system. The focused intensity at the target was 10 13 to 10 14 W/cm 2. The shock velocity was measured by using an optical streak camera. We have used various thicknesses of Al foil and 10 μm gold foil targets. Scaling of target velocity, with laser intensity has been done. The scaling of shock transit time with the foil thickness has been done. It is observed that at laser intensity > 1 x10 14 W/cm 2 the shock pressure measured from various target material are more than 10 Mbar. The scaling of shock transit time with target thickness has been measure. Also the scaling of shock velocity with laser intensity has been done for Aluminium and gold targets. The experimental observations are seen to match well with the simulations.