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Time-resolved x-ray absorption experiments have been performed on shocked tantalum. Using a single 100 ps synchrotron x-ray pulse, nanosecond-lived equilibrium states of shocked solid Ta have been measured by ${L}_{3}$-edge absorption spectroscopy. The energy shift and intensity change of the white line were measured up to 130 GPa and 2000 K. The experimental results are discussed in light of density functional theory calculations and FEFF simulations. The absence of occurrence of the hcp-$\ensuremath{\omega}$ phase is suggested from the analysis of the shape of the white line.

We have studied spallation in single crystal of metals under shock at very high strain rate. Our work has been devoted to understanding, and predicting the dynamic ductile damage processes of nucleation, growth and coalescence of voids in these extreme conditions of impact. Recovered sample only indicates final state of damage. Molecular Dynamics calculations are predicting the phenomenon over time. However we need experimental results to validate and improve simulations and models. X-ray tomography analyses are appropriate to extract pore volume distributions. Our study on ductile materials allowed us to conclude that experimental analyses exhibit two power laws attributed to growth and coalescence regimes. Moreover power law is scale invariance so it is possible to compare experiment (macroscopic) to calculation (microscopic). We show that there are good correlations between experimental and Molecular Dynamics pore volume distribution. Thanks X-ray microtomographies findings we progress in understanding the phenomenon of dynamic damage.

International audience; A high resolution picosecond laser imaging diagnostic has been developed for making high-resolution spatial measurements of ejecta particles moving at high velocities (a few km.s$^{-1}$). Preliminary results obtained with both visible (532 nm) and UV (355nm) lighting are presented for laser shock-driven tin ejecta experiments performed with different kind of surface defects. These results are compared with those obtained at LANL under high explosive loading using ultraviolet in-line Fraunhofer holography, and also with molecular dynamics (MD) simulations performed at lower space and time scales.

Synchrotron nanosecond time-resolved x-ray diffraction has been performed on dynamically compressed bismuth along various compression and release paths, hence exploring the Bi phase diagram up to 8 GPa and 600 K. Marked departures from the static phase diagram is observed. The sequence of structural changes is different upon compression and release. The Bi-III complex host-guest structure is never obtained. Instead the Bi-V phase is observed over a large domain. Melting of Bi-V and crystallization of the fluid into Bi-I are clearly identified on stress release. Supercooling and superheating deviations to the equilibrium melting line are observed. These observations on a prototypical system underline the possible deviations between the phase diagram obtained by dynamical compression and the one under static pressure.

Anticipating the generation of high velocity debris from shock-loaded specimens and the damage that their impacts may cause to nearby equipment is a major safety issue in applications involving shock waves, such as pyrotechnics [1] or inertial confinement fusion (ICF) experiments on large scale laser facilities [2]. Microjetting is one of the processes governing such debris generation. It is due to the interaction of a shock wave with a free surface presenting geometrical defects such as pits, cavities, scratches, or grooves, leading to material ejection from these defects, in the form of thin jets expanding ahead of the main surface and breaking up into small particles [3]. Over the last few years, we have used laser shock loading in order to expand microjetting investigations over ranges of small spatial scales (μm scale), extremely high loading rates (~ 107 s-1) and very short pressure pulses (a few ns) [4-11]. Optical shadowgraphy and Photonic Doppler Velocimetry (PDV) have been used to measure both jet tip and planar surface velocities [4-6], while attempts to infer fragments size distributions, to be compared with model predictions, have been made using either fast transverse shadowgraphy [7] or ejecta recovery [8]. More recently, picosecond x-ray radiography has been used to provide estimates of the density gradients along the jets and of the total ejected mass at different times after shock breakout [9-11]. Here, we present the development of a new picosecond laser imaging diagnostic intended to overcome the limitations of our current transverse optical shadowgraphy setup. We describe our experimental setup and show the results of our first experiments performed using both visible (532 nm) and UV (355 nm) lightning of the sample. These results are compared to those obtained at LANL under high explosive loading using ultraviolet in-line Fraunhofer holography [12], and also to molecular dynamics (MD) simulations performed by our colleagues at lower space and time scales [15-18].

We present in this paper recent advances in the high pressure domain provided by the introduction of time-resolved energy-dispersive XAS (EDXAS) techniques at synchrotrons. We highlight technical aspects and describe two modes of acquisition: the ‘movie’ mode, where the time resolution is given by the detector acquisition speed and the ‘pump-and-probe’ mode, where the time resolution is given by the delay between the pump and the probe. These two modes define a frontier in the time resolution, respectively above and below the ∼10 μs regime. In the former, examples of applications are chemical stability and reactions at high pressure and high temperature or probing the warm dense matter regime using rapid current ramps. In the latter, an example is given on studies of dynamically compressed matter, by coupling single-bunch EDXAS at high-brilliance synchrotron to a nanosecond high-power laser.

International audience; An ultrafast x-ray powder diffraction setup for laser-driven dynamic compression has been developed at the LULI2000 laser facility. X-ray diffraction is performed in reflection geometry from a quasi-monochromatic laser-generated plasma x-ray source. In comparison to a transmission geometry setup, this configuration allows us to probe only a small portion of the compressed sample, as well as to shield the detectors against the x-rays generated by the laser-plasma interaction on the front side of the target. Thus, this new platform facilitates probing of spatially and temporarily uniform thermodynamic conditions and enables us to study samples of a large range of atomic numbers, thicknesses, and compression dynamics. As a proof-of-concept, we report direct structural measurements of the bcc-hcp transition both in shock and ramp-compressed polycrystalline iron with diffraction signals recorded between 2θ ∼30° and ∼150°. In parallel, the pressure and temperature history of probed samples is measured by rear-side visible diagnostics (velocimetry and pyrometry).

International audience; Ion stopping experiments in plasma for beam energies of few hundred keV per nucleon are of great interest to benchmark the stopping-power models in the context of inertial confinement fusion and high-energy-density physics research. For this purpose, a specific ion detector on chemical-vapor-deposition diamond basis has been developed for precise time-of-flight measurements of the ion energy loss. The electrode structure is interdigitated for maximizing its sensitivity to low-energy ions, and it has a finger width of 100 μm and a spacing of 500 μm. A short single α-particle response is obtained, with signals as narrow as 700 ps at full width at half maximum. The detector has been tested with α-particle bunches at a 500 keV per nucleon energy, showing an excellent time-of-flight resolution down to 20 ps. In this way, beam energy resolutions from 0.4 keV to a few keV have been obtained in an experimental configuration using a 100 μg/cm2 thick carbon foil as an energy-loss target and a 2 m time-of-flight distance. This allows a highly precise beam energy measurement of δE/E ≈ 0.04%–0.2% and a resolution on the energy loss of 0.6%–2.5% for a fine testing of stopping-power models.

Understanding Warm Dense Matter (WDM), the state of planetary interiors, is a new frontier in scientific research. There exists very little experimental data probing WDM states at the atomic level to test current models and those performed up to now are limited in quality. Here, we report a proof-of-principle experiment that makes microscopic investigations of materials under dynamic compression easily accessible to users and with data quality close to that achievable at ambient. Using a single 100 ps synchrotron x-ray pulse, we have measured, by K-edge absorption spectroscopy, ns-lived equilibrium states of WDM Fe. Structural and electronic changes in Fe are clearly observed for the first time at such extreme conditions. The amplitude of the EXAFS oscillations persists up to 500 GPa and 17000 K, suggesting an enduring local order. Moreover, a discrepancy exists with respect to theoretical calculations in the value of the energy shift of the absorption onset and so this comparison should help to refine the approximations used in models.

International audience; This study presents the results of a large experimental campaign conducted on the Luli2000 laser facility. Thin targets of a commercial grade of porous graphite were submitted to high-power laser-driven shocks leading to their fragmentation. Many diagnostics were used such as high-speed time- and space-resolved imaging systems (shadowgraphy and photography), laser velocimetry (PDV and VISAR), debris collection and post-mortem X-ray tomography. They provided the loading levels into the targets, the spall strength of the material, the shape and size of debris and the localization of the subsurface cracks. The crossed data reduction of all the records showed their reliability and allowed to get a better insight into the damage phenomena at play in graphite. Thereby, four damage regimes, ranked according to their severity and loading level, were identified. It confirms that laser shocks are very complementary to classical impact tests (plates and spheres) since they ally two-dimensional loadings to the possibility of using both, in-situ and post-mortem diagnostics. Finally, the campaign shall be able to provide large and consistent data to develop and adjust reliable models for shock wave propagation and damage into porous graphite.

In this work, original shock experiments are presented. Laser-induced shock and shear wave propagations have been observed in an epoxy resin, in the case of femtosecond laser irradiation. A specific time-resolved shadowgraphy setup has been developed using the photoelasticimetry principle to enhance the shear wave observation. Shear waves have been observed in epoxy resin after laser irradiation. Their propagation has been quantified in comparison with the main shock propagation. A discussion, hinging on numerical results, is finally given to improve understanding of the phenomenon.; International audience; In this work, original shock experiments are presented. Laser-induced shock and shear wave propagations have been observed in an epoxy resin, in the case of femtosecond laser irradiation. A specific time-resolved shadowgraphy setup has been developed using the photoelasticimetry principle to enhance the shear wave observation. Shear waves have been observed in epoxy resin after laser irradiation. Their propagation has been quantified in comparison with the main shock propagation. A discussion, hinging on numerical results, is finally given to improve understanding of the phenomenon.

We present detonation wave profiles measured in T2 (97 wt. % TATB) and TX1 (52 wt. % TATB and 45 wt. % HMX) high explosives. The experiments consisted in initiating a detonation wave in a 15 mm diameter cylinder of explosive using an explosive wire detonator and an explosive booster. Free surface velocity wave profiles were measured at the explosive/air interface using a Photon Doppler Velocimetry system. We demonstrate that a comparison of these free surface wave profiles with those measured at explosive/window interfaces in similar conditions allows to bracket the von Neumann spike in a narrow range. For T2, our measurements show that the spike pressure lies between 35.9 and 40.1 GPa, whereas for TX1, it lies between 42.3 and 47.0 GPa. The numerical simulations performed in support to these measurements show that they can be used to calibrate reactive burn models and also to check the accuracy of the detonation products equation of state at low pressure.

We present a combined molecular dynamics and kinetic study of a carbon cluster aggregation process in thermodynamic conditions relevant for the detonation products of oxygen deficient explosives. Molecular dynamics simulations with the LCBOPII potential under gigapascal pressure and high temperatures indicate that (i) the cluster motion in the detonation gas is compatible with Brownian diffusion and (ii) the coalescence probability is 100% for two clusters entering the interaction cutoff distance. We used these results for a subsequent kinetic study with the Smoluchowski model, with realistic models applied for the physical parameters such as viscosity and cluster size. We found that purely aggregational kinetics yield too fast clustering, with moderate influence of the model parameters. In agreement with previous studies, the introduction of surface reactivity through a simple kinetic model is necessary to approach the clustering time scales suggested by experiments (1000 atoms after 100 ns, 10 000 atoms after 1 μs). However, these models fail to reach all experimental criteria simultaneously and more complex modelling of the surface process seems desirable to go beyond these current limitations.

We have performed time-resolved free surface velocity measurements of the expanding products from the detonation of a TATB based high explosive composition, using both Heterodyne Velocimetry (i.e. Photon Doppler Velocimetry) and digital high speed shadowgraphy. The free surface velocity waveforms exhibit features which can be directly related to charateristics of the reaction zone. This allows to estimate the von Neumann spike pressure to PVN ≃41 GPa and the duration of the reaction zone to 400-500 ns, in good agreement with previous studies. 2D Eulerian direct numerical simulations performed with the wide-ranging equation of state and reaction rate model developed by Wescott, Scott Stewart and Davis are found to be in very good agreement with our experimental results.

A good description of the expansion of the detonation products from a chemical explosion is of fundamental importance because it constrains the ballistic performance of the explosive.We describe in this paper an experimental study of the free expansion of detonation products of an insensitive TATB-based explosive by measuring the free surface velocity of the detonating explosive with a PDV velocimeter system. Indeed, recent experiments [1] have demonstrated the ability of such system to record the free surface velocity of a detonating explosive, and also potentially the detonation velocity inside the explosive just before the shock breakout, if the explosive is not entirely opaque in the near IR walelengths, which is the case of most TATB based explosives. PDV appears to be a very promising recording technique for such measurements, because it offers a good time resolution (close to 1 ns) and ability to record over very long durations which is required to measure the reaction product expansion over a large volume range. We also used digital high-speed shadowgraphy to characterize the shape and speed of the products as they release from the bare charge free surface. The results allow to give new insight into the reactions zone of TATB based high explosive. They are compared with numerical simulations performed with different reactive flow models.

Laser shock processing (LSP) is an emerging industrial process in the field of surface treatment with particular application to the improvement of fatigue and corrosion properties. In the standard configuration, the metal sample is coated with a sacrificial layer in order to protect it from detrimental thermal effects, and a water overlay is used to improve the mechanical coupling by a confining like effect. Whereas the induced mechanical effects are now well understood, very few studies have been realized concerning the thermal effects. For this purpose, the knowledge of the confined plasma microscopic parameters has a great importance. A complete model describing the laser-liquid-metal interaction is presented. The model predicts the time evolution of the plasma parmmeters (temperature, density, ionization) and allows us to compute the induced pressure and temperature in the metal sample. By comparing the numerical results with various experimental measurements, predictions can be made concerning the best laser irradiation conditions for LSP.

International audience; Dynamic fragmentation in the liquid state after shock-induced melting, usually referred to as micro-spallation, is an issue of great interest for both basic and applied sciences. Recent efforts have been devoted to the characterization of the resulting ejecta, which consist in a cloud of fine molten droplets. Major difficulties arise from the loss of free surface reflectivity at shock breakout and from the wide distribution of particle velocities within this cloud. We present laser shock experiments on tin and aluminium, to pressures ranging from about 70 to 160GPa, with complementary diagnostics including a photonic Doppler velocimeter set at a small tilt angle from the normal to the free surface, which enables probing the whole cloud of ejecta. The records are roughly consistent with a one-dimensional theoretical description accounting for laser shock loading, wave propagation, phase transformations, and fragmentation. The main discrepancies between measured and calculated velocity profiles are discussed in terms of edge effects evidenced by transverse shadowgraphy.

This paper presents numerical calculations of residual stresses induced by shock waves generated by laser plasma in water confinement regime. Results are in agreement with residual stresses measurements on samples irradiated with square laser pulse of 3 ns. Effects of thermo-absorbing coatings are discussed. In particularly, without coating, compressive stresses can not be generated. However, with small spots laser, the 2D propagation of the laser-plasma reduces the thermal loadings on surface and limits the depth for which tensile stresses are generated.This paper presents numerical calculations of residual stresses induced by shock waves generated by laser plasma in water confinement regime. Results are in agreement with residual stresses measurements on samples irradiated with square laser pulse of 3 ns. Effects of thermo-absorbing coatings are discussed. In particularly, without coating, compressive stresses can not be generated. However, with small spots laser, the 2D propagation of the laser-plasma reduces the thermal loadings on surface and limits the depth for which tensile stresses are generated.