Laser-driven Shock Waves Research Articles

Measurement of laser driven shock wave transit time through thin aluminium targets by optical shadowgraphy

Laser driven shock wave transit time in thin aluminium targets was experimentally estimated by determining the shock emergence time at the rear of thin aluminium foils of varying thickness from 5 to 35 μm. A 20 J, 5 ns Nd:glass laser was focused to produce laser intensity of 1012 to 5 × 1013 W/cm2 on the targets which were placed in vacuum. Target foil movement was measured to an accuracy of 10 μm using optical shadowgraphy technique. This technique was used to accurately measure the shock transit time by recording the optical shadowgrams at various instants of time and thus identify the instant at which the foil is just set into motion. Shock transit time measured in foils of different thickness can give the value of shock velocity at a given laser intensity. Target motion recorded by shadowgraphy can also give the target foil velocity from which shock pressure can be estimated. Experimental values of shock transit time, shock velocity and shock pressure were observed to agree well with the values using one-dimensional multi-group radiation hydrodynamic simulations.

Shock compression of quartz in the high-pressure fluid regime

The Hugoniot of quartz has been measured using laser-driven shock waves with pressures from 2 to 15 Mbars. Within this pressure range silica transforms from a liquid near melt into a dense plasma. Results are in good agreement with previous studies in part of this range performed using explosive- and nuclear-driven shocks indicating the absence of time-dependent effects for time scales between several hundred picoseconds and several hundred microseconds. These data combined with earlier data at lower pressures clearly show the increasing compressibility of silica as it transitions from solid to liquid to dense plasma regimes.

Novel crystalline carbon-cage structure synthesized from laser-driven shock wave loading of graphite

We report a novel crystalline carbon-cage structure synthesized from laser-driven shock wave loading of a graphite-copper mixture to about 14+/-2 GPa and 1000 +/- 200 K. Quite unexpectedly, it can be structurally related to an extremely compressed three-dimensional C60 polymer with random displacement of C atoms around average positions equivalent to those of distorted C60 cages. Thus, the present carbon-cage structure represents a structural crossing point between graphite interlayer bridging and C60 polymerization as the two ways of forming diamond from two-dimensional and molecular carbon.

Mean-field potential calculations of shock-compressed porous carbon

The mean-field potential approach with first-principles total energy data as input is used to investigate shock-compressed carbon with initial densities of 3.51, 2.2, 1.85, and $1.6\phantom{\rule{0.3em}{0ex}}\mathrm{g}∕{\mathrm{cm}}^{3}$ up to $1400\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. We have calculated the shock Hugoniot, and the temperature and electronic contribution to the heat capacity along the Hugoniot. While excellent agreement with underground nuclear explosion data is obtained, our results do not show the high compressibility of carbon at megabar pressures indicated by recent laser-driven shock wave experiments.

Properties of fluid deuterium under double-shock compression to several Mbar

The compressibility of fluid deuterium up to several Mbar has been probed using laser-driven shock waves reflected from a quartz anvil. Combining high-precision (∼1%) shock velocity measurements with the double-shock technique, where differences in equation of state (EOS) models are magnified, has allowed better discrimination between theoretical predictions in the second-shock regime. Double-shock results are in agreement with the stiffer EOS models—which exhibit roughly fourfold single-shock compression—for initial shocks up to 1 Mbar and above 2 Mbar, but diverge from these predictions in between. Softer EOS models—which exhibit sixfold single-shock compression at 1 Mbar—overestimate the reshock pressure for the entire range under study.

Hugoniot data for carbon at megabar pressures.

We present an experimental point for the carbon equation of state (EOS) at megabar pressures, obtained by laser-driven shock waves. The rear side emissivity of "two-materials two-steps" targets (Al-C) was recorded with space and time resolution and, by applying the impedance mismatch method, allowed a direct determination of relative EOS points. Experiments were performed at the PALS and LULI laboratories using carbon samples with two different values of initial density, in order to explore a wider region of the phase diagram. Previously unreached pressures were obtained. The results are compared with previous experiments and with available theoretical models and seem to show a high compressibility of carbon at megabar pressures.

レーザー誘起衝撃波圧縮を用いた状態方程式研究 3.レーザー誘起衝撃波圧縮による状態方程式計測 3.2 慣性核融合燃料ペレットに関する状態方程式計測実験

Equation-of-State (EOS) experiments, based on an impedance matching scheme, were performed on plastic materials using laser-driven shock waves. The hugoniot of polystyrene, polyimide, and deuterated-polyethylene, each of which are materials of interest in inertial fusion energy studies, were measured. The EOS points were determined with good accuracy in very wide pressure regime.

Coupling static and dynamic compressions: first measurements in dense hydrogen

We demonstrate here a laser-driven shock wave in a hydrogen sample, pre-compressed in a diamond anvil cell. The compression factors of the dynamic and static techniques are multiplied. This approach allows access to a family of Hugoniot curves which span the P–T phase diagram of fluid hydrogen to high density. In this first-of-its-kind experiment, two hydrogen Hugoniot curves have been partially followed starting from pre-compression at pressures of 0.7 GPa and 1.2 GPa. Optical reflectance probing at two wavelengths reveals the onset of the conducting fluid state. The boundary line to conducting fluid hydrogen is suggested.

Optical properties of highly compressed polystyrene using laser-driven shockwaves

Plastic is a common material used for laboratory astrophysics and inertial confinement fusion. Experimental measurements of the optical properties of shock compressed polystyrene in the strongly coupled and correlated regime (0.7 Mbar<P<1.7 Mbar; 0.5<T<1.3 eV) are reported. A VISAR (Velocity Interferometer System for Any Reflector) system was used in addition to self-emission recording on a streak camera. This allowed a simultaneous access to reflectivity, instantaneous shock velocity and temperature. Mean ionization and conductivity of the material have then been deduced through the Drude model. The values found are more than an order of magnitude greater than published ones in this temperature domain.

Equation-of-state measurements of polyimide at pressures up to 5.8 TPa using low-density foam with laser-driven shock waves

The laser-driven equation-of-state (EOS) experiments for polyimide are presented. The experiments were performed with emission measurements from the rear sides of shocked targets at up to a laser intensity of 10(14) W/cm(2) or higher with 351 nm wavelength and 2.5 ns duration. Polyimide Hugoniot data were obtained up to 0.6 TPa with good accuracy. Applying low-density foam ablator to the EOS unknown material, we also obtained the data at a highest pressure of 5.8 TPa in the nonmetal materials. Those data were in agreement with the theoretical curves.

Specific energy for pulsed laser rock drilling

Application of advanced high power laser technology to oil and gas well drilling has been attracting significant research interests recently among research institutes, petroleum industries, and universities. Potential laser or laser-aided oil and gas well drilling has many advantages over the conventional rotary drilling, such as high penetration rate, reduction or elimination of tripping, casing, and bit costs, and enhanced well control, perforating and side-tracking capabilities. The energy required to remove a unit volume of rock, namely the specific energy (SE), is a critical rock property data that can be used to determine both the technical and economic feasibility of laser oil and gas well drilling. When a high power laser beam is applied on a rock, it can remove the rock by thermal spallation, melting, or vaporization depending on the applied laser energy and the way the energy is applied. The most efficient rock removal mechanism would be the one that requires the minimum energy to remove a unit volume of rock. Samples of sandstone, shale, and limestone were prepared for laser beam interaction with a 1.6 kW pulsed Nd:yttrium–aluminum–garnet laser beam to determine how the beam size, power, repetition rate, pulse width, exposure time and energy can affect the amount of energy transferred to the rock for the purposes of spallation, melting, and vaporization. The purpose of the laser rock interaction experiment was to determine the optimal parameters required to remove a maximum rock volume from the samples while minimizing energy input. Absorption of radiant energy from the laser beam gives rise to the thermal energy transfer required for the destruction and removal of the rock matrix. Results from the tests indicate that each rock type has a set of optimal laser parameters to minimize specific energy (SE) values as observed in a set of linear track and spot tests. As absorbed energy outpaces heat diffusion by the rock matrix, local temperatures can rise to the melting points of the minerals and quickly increase observed SE values. Tests also clearly identified the spallation and melting zones for shale samples while changing the laser power. The lowest SE values are obtained in the spalling zone just prior to the onset of mineral melt. The laser thermally spalled and saw mechanically cut rocks show similarity of surface microstructure. The study also found that increasing beam repetition rate within the same material removal mechanism would increase the material removal rate, which is believed due to an increase of maximum temperature, thermal cycling frequency, and intensity of laser-driven shock wave within the rock.

Laser driven shock wave experiments for equation of state studies at megabarpressures

We present the results from laser driven shock wave experiments for equation ofstate (EOS) studies of gold metal. An Nd:YAG laser chain (2 J, 1.06 μmwavelength, 200 ps pulse FWHM) is used to generate shocks in planar Al foils andAl + Au layered targets. The EOS of gold in the pressure range of 9–13 Mbar isobtained using the impedance matching technique. The numerical simulationsperformed using the one-dimensional radiation hydrodynamic code support theexperimental results. The present experimental data show remarkableagreement with the existing standard EOS models and with other experimentaldata obtained independently using laser driven shock wave experiments.

Numerical simulation study of laser-driven shock wave propagation in planaraluminium foils

A comprehensive numerical simulation study of laser-driven shockwave propagation in planar aluminium foils, 20– 50μ m, isperformed using the one-dimensional radiation hydrodynamic code MULTI. Theeffect of the spatial mesh size on the shock velocity and peak shock pressure isfound to be significant and the optimum mesh size is obtained. Shock velocitiesand maximum pressure are calculated through simulations for two sets oflaser intensities used in an experiment (Fu S, Gu Y, Wu J and Wang S1995 Phys. Plasmas 2 3461). By using different sets of laser absorptioncoefficient values we determine the appropriate values reproducing theexperimental results. We demonstrate that the simulations can be used as aneffective tool for benchmark calculation of laser absorption coefficients.

Similarity solution for laser-driven shock waves in a dust-laden gas with internal heat transfer effects

The non-adiabatic flow behind a laser-driven strong shock wave propagating in a mixture of gas and small solid particles is the subject of this paper. A similarity solution which accounts for the influence of internal heat fluxes due to high temperatures achieved at the centre has been obtained. The heat fluxes in the blast-wave equations are considered in terms of Fourier's law for conduction and by an expression for thermal radiation of the diffusion type. As for adiabatic flow, it is assumed that the equilibrium-flow condition is maintained and that the variable laser energy is completely absorbed at the shock front according to a time-dependent power law. The formulation results in a two-point boundary-value problem. The effects of a parameter characterising the various energy input of the blast wave on the similarity solution as well as on its limits have been examined. The computations have been performed for various values of mass concentration of the solid particles and for the ratio of density of solid particles to the constant initial density of gas.

Equation of state data for iron at pressures beyond 10 Mbar.

We present equation of state points for iron, in the pressure range 10-45 Mbar, the first obtained with laser-driven shock waves. The experiment has been performed with the high energy laser Phebus, optically smoothed with Kinoform phase plates. Our results double the set of existing experimental data at very high pressures showing good agreement with the predictions of the quotidian equation of state model and with previous results.

Absolute equation of state measurements of iron using laser driven shocks

First absolute equation of state measurements obtained for iron with laser driven shock waves are presented. The shock velocity and the free surface velocity of compressed iron have been simultaneously measured by using a VISAR diagnostic, and step targets. The pressure range 1–8 Mbar has been investigated, which is directly relevant to planetary physics. The experiments have been performed at the Laboratoire pour l’Utilisation des Lasers Intenses of the Ecole Polytechnique.

Calculation of a deuterium double shock Hugoniot from ab initio simulations.

We calculate the equation of state of dense deuterium with two ab initio simulation techniques, path integral Monte Carlo and density functional theory molecular dynamics, in the density range of 0.67 < or = rho < or = 1.60 g cm(-3). We derive the double shock Hugoniot and compare with the recent laser-driven double shock wave experiments by Mostovych et al. [Phys. Rev. Lett. 85, 3870 (2000)]. We find excellent agreement between the two types of microscopic simulations, but a significant discrepancy with the laser-driven shock measurements.

Computer simulations for shock-compressed liquid deuterium: Failure of density-functional theory and molecular dynamics

We show that the disagreement of recent laser driven shock wave experiments for liquid deuterium with Hugoniots calculated with the generalized gradient approximation molecular dynamics (GGA-MD) method stems from the underestimate of the metalization density associated with density functional theory (DFT). This leads to an enhanced degree of thermally induced molecular dissociation with the result that computer simulations fail to achieve the compression observed experimentally. Scaling of the GGA-MD Hugoniot to hypothetical GW Hugoniot results, using the ratio of volumes at which the GW and DFT band gaps close, leads to a prediction in good agreement with experiment.

Similarity solution for laser-driven shock waves in a particle-laden gas

A similarity solution has been obtained for a laser-driven strong shock wave propagating in a mixture of gas and small solid particles. It is assumed that the equilibrium-flow condition is maintained and the variable laser energy is completely absorbed at the shock front according to a time-dependent power law. The similarity solution is valid for adiabatic flow as long as the effect of the counter pressure is neglected. The effects of a parameter characterising the various energy input of the blast wave on the similarity solution as well as on its limits have been examined. The computations have been performed for various values of mass concentration of the solid particles and for the ratio of density of solid particles to the constant-initial density of gas.

Use of low-density foams as pressure amplifiers in equation-of-state experiments with laser-driven shock waves

The applicability of foams to equation of state experiments with laser-produced shocks has been studied. The pressure increase due to impedance mismatch at the payload-foam interface was measured experimentally using sub-ns laser pulses smoothed with phase zone plates. Foams of density in the range 5-900 mg/cm(3) and of thicknesses of 50-150 microm were used. A model has been developed to study pressure amplification and the conditions under which the shock is stationary. Two-step two-material targets, allowing simultaneous measurements of the shock velocities in the two materials, were then used to obtain relative equation of state data. Pressures higher than 100 Mbar were achieved in gold.