A. Lazicki

Ramp compression of diamond to five terapascals

The recent discovery of more than a thousand planets outside our Solar System, together with the significant push to achieve inertially confined fusion in the laboratory, has prompted a renewed interest in how dense matter behaves at millions to billions of atmospheres of pressure. The theoretical description of such electron-degenerate matter has matured since the early quantum statistical model of Thomas and Fermi, and now suggests that new complexities can emerge at pressures where core electrons (not only valence electrons) influence the structure and bonding of matter. Recent developments in shock-free dynamic (ramp) compression now allow laboratory access to this dense matter regime. Here we describe ramp-compression measurements for diamond, achieving 3.7-fold compression at a peak pressure of 5 terapascals (equivalent to 50 million atmospheres). These equation-of-state data can now be compared to first-principles density functional calculations and theories long used to describe matter present in the interiors of giant planets, in stars, and in inertial-confinement fusion experiments. Our data also provide new constraints on mass–radius relationships for carbon-rich planets.

Powder diffraction from solids in the terapascal regime

A method of obtaining powder diffraction data on dynamically compressed solids has been implemented at the Jupiter and OMEGA laser facilities. Thin powdered samples are sandwiched between diamond plates and ramp compressed in the solid phase using a gradual increase in the drive-laser intensity. The pressure history in the sample is determined by back-propagation of the measured diamond free-surface velocity. A pulse of x rays is produced at the time of peak pressure by laser illumination of a thin Cu or Fe foil and collimated at the sample plane by a pinhole cut in a Ta substrate. The diffracted signal is recorded on x-ray sensitive material, with a typical d-spacing uncertainty of ~0.01 Å. This diagnostic has been used up to 0.9 TPa (9 Mbar) to verify the solidity, measure the density, constrain the crystal structure, and evaluate the strain-induced texturing of a variety of compressed samples spanning atomic numbers from 6 (carbon) to 82 (lead). Further refinement of the technique will soon enable diffraction measurements in solid samples at pressures exceeding 1 TPa.

Compression Freezing Kinetics of Water to Ice VII

Time-resolved x-ray diffraction (XRD) of compressed liquid water shows transformation to ice VII in 6xa0nsec, revealing crystallization rather than amorphous solidification during compression freezing. Application of classical nucleation theory indicates heterogeneous nucleation and one-dimensional (e.g., needlelike) growth. These first XRD data demonstrate rapid growth kinetics of ice VII with implications for fundamental physics of diffusion-mediated crystallization and thermodynamic modeling of collision or impact events on ice-rich planetary bodies.

In situ X-ray diffraction measurement of shock-wave-driven twinning and lattice dynamics

Pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation is challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum—an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. The techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.

X-ray area backlighter development at the National Ignition Facility (invited).

1D spectral imaging was used to characterize the K-shell emission of Z ≈ 30-35 and Z ≈ 40-42 laser-irradiated foils at the National Ignition Facility. Foils were driven with up to 60 kJ of 3ω light, reaching laser irradiances on target between 0.5 and 20 × 10(15) W/cm(2). Laser-to-X-ray conversion efficiency (CE) into the Heα line (plus satellite emission) of 1.0%-1.5% and 0.15%-0.2% was measured for Z ≈ 30-32 and Z ≈ 40-42, respectively. Measured CE into Heα (plus satellite emission) of Br (Z = 35) compound foils (either KBr or RbBr) ranged between 0.16% and 0.29%. Measured spectra are compared with 1D non-local thermodynamic equilibrium atomic kinetic and radiation transport simulations, providing a fast and accurate predictive capability.

Measurement of Body-Centered-Cubic Aluminum at 475 GPa [Observation of Body-Centered-Cubic Aluminum at 475 GPa]

Nanosecond inxa0situ x-ray diffraction and simultaneous velocimetry measurements were used to determine the crystal structure and pressure, respectively, of ramp-compressed aluminum at stress states between 111 and 475xa0GPa. The solid-solid Al phase transformations, fcc-hcp and hcp-bcc, are observed at 216±9 and 321±12u2009u2009GPa, respectively, with the bcc phase persisting to 475xa0GPa. The high-pressure crystallographic texture of the hcp and bcc phases suggests close-packed or nearly close-packed lattice planes remain parallel through both transformations.

Absolute Hugoniot measurements from a spherically convergent shock using x-ray radiography

The canonical high pressure equation of state measurement is to induce a shock wave in the sample material and measure two mechanical properties of the shocked material or shock wave. For accurate measurements, the experiment is normally designed to generate a planar shock which is as steady as possible in space and time, and a single state is measured. A converging shock strengthens as it propagates, so a range of shock pressures is induced in a single experiment. However, equation of state measurements must then account for spatial and temporal gradients. We have used x-ray radiography of spherically converging shocks to determine states along the shock Hugoniot. The radius-time history of the shock, and thus its speed, was measured by radiographing the position of the shock front as a function of time using an x-ray streak camera. The density profile of the shock was then inferred from the x-ray transmission at each instant of time. Simultaneous measurement of the density at the shock front and the shock speed determines an absolute mechanical Hugoniot state. The density profile was reconstructed using the known, unshocked density which strongly constrains the density jump at the shock front. The radiographic configuration and streak camera behavior were treated in detail to reduce systematic errors. Measurements were performed on the Omega and National Ignition Facility lasers, using a hohlraum to induce a spatially uniform drive over the outside of a solid, spherical sample and a laser-heated thermal plasma as an x-ray source for radiography. Absolute shock Hugoniot measurements were demonstrated for carbon-containing samples of different composition and initial density, up to temperatures at which K-shell ionization reduced the opacity behind the shock. Here we present the experimental method using measurements of polystyrene as an example.

Erratum: Measurement of Body-Centered-Cubic Aluminum at 475 GPa [Phys. Rev. Lett. 119 , 175702 (2017)]

This corrects the article DOI: 10.1103/PhysRevLett.119.175702.

Lithographically fabricated gratings for the interferometric measurement of material shear moduli under extreme conditions

Electron beam lithography and photolithography were used to fabricate diffraction gratings on targets for laser-driven shock-wave experiments. This target design was used with an optical interferometric system to measure transverse wave motion of the target during dynamic (shock-wave) compression. A wedged-shaped diamond substrate and reflective grating on the samples surface allowed detection of transverse motion. Proof of principle tests on single-crystal 〈100〉 Si samples gave a transverse wave speed of 5.9u2009km/s at 5u2009GPa and a shear modulus of 81u2009GPa. This experimental design has tremendous potential, including the possibility of measuring the shear properties of pure iron at Earth core conditions.Electron beam lithography and photolithography were used to fabricate diffraction gratings on targets for laser-driven shock-wave experiments. This target design was used with an optical interferometric system to measure transverse wave motion of the target during dynamic (shock-wave) compression. A wedged-shaped diamond substrate and reflective grating on the samples surface allowed detection of transverse motion. Proof of principle tests on single-crystal 〈100〉 Si samples gave a transverse wave speed of 5.9u2009km/s at 5u2009GPa and a shear modulus of 81u2009GPa. This experimental design has tremendous potential, including the possibility of measuring the shear properties of pure iron at Earth core conditions.