Shock compression of deuterium near 100 GPa pressures

The shock-compression curve (Hugoniot) of D2 near 100 GPa pressures (1 Mbar) has been contro-versial because the two published measurements have limiting compressions of fourfold and sixfold. Our purpose is to examine published experimental results to decide which, if either, is probably correct. The published Hugoniot data of low-Z diatomic molecules have a universal behavior. The deuterium data of Knudson et al. (fourfold limiting compression) have this universal behavior, which suggests that Knudson et al. are correct and shows that deuterium behaves as other low-Z elements at high tem-peratures. In D2, H2, N2, CO, and O2, dissociation completes and average kinetic energy dominates average potential energy above approximately 60 GPa. Below approximately 30 GPa, D2, H2, N2, CO, and O2 are diatomic. D2 dissociation is accompanied by a temperature-driven nonmetal-metal transition at approximately 50 GPa.     

Quasi-isentropic compression of liquid argon up to 500 GPa

The compressibility of liquid argon up to pressures ∼500 GPa has been investigated experimentally. The argon was compressed by a cylindrical shell accelerated by the detonation products of an explosive. The density was recorded by the gamma-graphic method and the pressure was determined from the gas-dynamic calculations. Comparing the experimental and computational results showed that the compression process studied is isentropic to a quite high degree. The compression of liquid argon up to a density of 7.3 g/cm³ did not show any clear anomalies associated with a structural transition or metallization. Zh. éksp. Teor. Fiz. 111, 2099–2105 (June 1997)     

Critical temperature of metallic hydrogen at a pressure of 500 GPa

Phase transitions of the layered antiferromagnetic Ising model on a cubic lattice with allowance for intralayer next nearest neighbor interactions in the range of 0.0 ? r < 1.0 have been studied on the basis of the replica algorithm by the Monte Carlo method. The character of phase transitions has been analyzed on the basis of the histogram method and the Binder cumulant method. The phase diagram of the dependence of the critical temperature on the next nearest neighbor interaction has been constructed. It has been shown that a secondorder phase transition is observed in the interval of 0.0 ? r ? 0.5 and for the value r = 0.9 and a first-order phase transition is observed in the interval of 0.6 ? r < 0.8.     

Stable structure of metallic hydrogen at a pressure of 500 GPa

The structural, electron, phonon, and other characteristics of the metallic normal phase of hydrogen at a pressure of 500 GPa are calculated by an ab initio mathematical simulation. It is shown that metallic hydrogen having a lattice with the I41/amd symmetry is a stable phase at a high hydrostatic compression pressure. The resulting structure has the spectrum of phonons stable with respect to the decay.     

Shock cooling of liquid nitrogen and superfluid helium

Abstract

Superfluid Helium (11) and liquid nitrogen are the only liquids which have been shown experimentally, to exhibit shock cooling. In the present paper we use the Landau model to demonstrate theoretically that the roton gap, which decreases with increasing density, plays the same role leading to shock cooling in liquid helium as the dissociation energy does in liquid nitrogen.     

High pressure compression of CeB6 up to 20 GPa

The volume compression of CeB₆ has been measured by X-ray diffraction in a diamond anvil cell up to 20 GPa. At normal pressure the bulk modulus and its first pressure derivative have been determined to be equal to 166 GPa and 3.15 respectively. The bulk modulus is not reduced by the Kondo effect and no indication of any second or first order transition was found.     

Measurement of the compressibility of a deuterium plasma at a pressure of 1800 GPa

The thermodynamic properties of a highly compressed deuterium plasma have been measured using an explosive spherical experimental chamber. The experiment has been performed with an X-ray diffraction complex consisting of three betatrons and a multichannel optoelectronic system of the detection of X-ray images of the process of the explosive spherical compression of deuterium. The density of the shock-compressed deuterium plasma ρ = (4.3 ± 0.7) g/cm³ at the pressure P = 1830 GPa has been detected at the initial pressure of gaseous deuterium P ₀ = 267 atm and the temperature T ₀ = 10.5°C. Under such conditions, the plasma is strongly nonideal (Γ ～ 450) with the degenerate (nλ _e ³ ～ 280) electron component and with an electron density of about 2.8 × 10²³ cm^?3.     

Mathematical simulation of the compression process of a vapor bubble at a pressure increase in the surrounding liquid

The thermophysical and hydrodynamic processes in a spherical vapor bubble and the surrounding liquid at increasing external pressure are investigated by using a numerical simulation method. The investigation is performed on the basis of a new mathematical model belonging to the class of models of homobaric bubbles (the pressure in the bubble is homogeneous at nonhomogeneous temperature and density). The model takes into account the following main physical effects: the viscosity of the liquid, the heat conductivity of the liquid and vapor, the surface tension, and the phase transitions at the bubble surface. An energy equation taking into account convective heat transfer and viscous dissipation in the liquid is used to calculate the temperature fields in the liquid and vapor. The model also takes into account the dependence of the thermophysical properties on the temperature. A distinctive feature of the proposed model is that the integral conservation law of the system’s total energy (including the kinetic energy of the liquid, the surface energy, and the internal energy of the liquid and vapor) is exactly satisfied (without allowance for the kinetic energy of the vapor). As a result of the numerical simulation of the compression of vapor bubbles in water, we obtained data for the major characteristics of the process at considerable degrees of compression. It is shown that the heat and mass transfer between the vapor in a bubble and the surrounding liquid considerably slow down the temperature increase in the bubble.     

Structure of liquid iron at pressures up to 58 GPa

We report structural data on liquid iron at pressures up to 58 GPa measured by x-ray scattering in a laser heated diamond anvil cell. The determined structure factor preserves essentially the same shape along the melting curve. Our data demonstrate that liquid iron at high pressures is a close-packed hard-sphere liquid. The results place important constraints on the thermodynamic and transport properties of liquid iron and the melting curve of iron.     

Quasi-isentropic compression of dense gaseous helium at pressures up to 500 GPa

The thermodynamic parameters??pressure and density??of quasi-isentropically compressed helium have been measured in a pressure range of 100?C500 GPa. A thermodynamic model that satisfactorily describes the behavior of strongly compressed helium in a wide range of compression parameters has been proposed.     

Use of a wave reverberation technique to infer the density compression of shocked liquid deuterium to 75 GPa

A novel approach was developed to probe density compression of liquid deuterium (L-D2) along the principal Hugoniot. Relative transit times of shock waves reverberating within the sample are shown to be sensitive to the compression due to the first shock. This technique has proven to be more sensitive than the conventional method of inferring density from the shock and mass velocity, at least in this high-pressure regime. Results in the range of 22-75 GPa indicate an approximately fourfold density compression, and provide data to differentiate between proposed theories for hydrogen and its isotopes.     

Anomaly in the conductivity of shock-compressed nickel at a pressure of ∼23 GPa

In the pressure range 14–35 GPa we have measured the resistance of shock-compressed nickel. Its abrupt decrease at; ∼23 GPa is noted, and the boundaries of the existence of this anomaly (±1 GPa) are determined. It is shown that the observed anomaly can be linked with a structural rearrangement of the electron shells of nickel. Fiz. Tverd. Tela (St. Petersburg) 41, 369–371 (March 1999)     

Volume compression of thallium to 45 GPa

Abstract

High-pressure structural transition and volume compression for thallium were investigated to 45 GPa in a diamond anvil cell using the angular dispersive X-ray diffraction technique. Except for the known polymorphic transition at 3.7 GPa, no other structural change was observed in this pressure range. The equation of state of the high pressure phase has been obtained: its initial bulk modulus, B₀ = 33.1 GPa, is lower by 10% than that of the hexagonal phase at normal pressure.     

Ramp compression of tantalum to 330 GPa

We report on the stress–density and rate-dependent response for Ta, ramp compressed to 330?GPa with strain rates up to 5?×?10⁸?s^?1. We employ temporally shaped laser drives to compress Ta stepped foils over several to tens of nanoseconds. Lagrangian wave-profile analysis reveals a stress–density relationship which falls below the Hugoniot, above the hydrostat, and is consistent with ramp-compression experiments at lower strain rates. We also report on the peak elastic stress prior to plastic deformation as a function of strain rate for laser-driven ramp and shock-compression data spanning the 1–50?×?10⁷?s^?1 strain-rate range. When combined with previously published lower strain data (10¹–10⁷?s^?1), we observe a change in rate dependence, suggesting a transition from thermally activated to defect-limited (phonon drag) dislocation motion occurring at a strain rate of about 10⁵?s^?1.     

Volume compression of CuCl to 7 GPa

The unit cell volume of CuCl as a function of pressure has been measured up to 7 GPa (giga Pascals). The compression behaviour is quite normal. The analysis of the compression data gives 40·3±1·5 GPa for the bulk modulus of the zinc blende phase. The zinc blende phase transforms to a tetragonal phase at 5·5 GPa, the volume change associated with the transformation being 12%. A comparison of the bulk modulus of CuCl with those of CuBr and CuI indicates that an anomaly exists in this group.     

Measurement of the quasi-isentropic compressibility of a helium plasma at a pressure of about 5000 GPa

The quasi-isentropic compressibility of a helium plasma has been measured using a spherical experimental chamber, as well as an X-ray diffraction complex consisting of three betatrons and a multichannel optoelectronic system for the detection of X-ray images. The density of the compressed helium plasma of about 8 g/cm³ has been obtained in the experiment at a pressure of 5000 GPa. Analysis of the data indicates that helium at the measured parameters is in a single ionized state.     

Measurement on Effective Shear Viscosity Coefficient of Iron under Shock Compression at 100GPa

The oscillatory damping curve of a shock front propagating in iron shocked to 103 GPa is measured by use of two-stage light-gas gun and electric pin techniques. The corresponding effective shear viscosity coefficient is deduced to be about 2000 Pa.s from Miller and Ahrens＇ formula. The result is consistent with that of Mineev＇s data at 31GPa, while it is higher by five orders than the predictions based on the static measurements at about 5 GPa and 2000K and molecular dynamic simulation up to 135-375 GPa and 4300-6000 K, and the discussions are presented.     

Properties of shock-compressed liquid krypton at pressures of up to 90 GPa

The following quantities of shock-compressed liquid krypton are measured behind a plane shock front at pressures up to 90 GPa: compressibility up to densities of 7 g/cm³, brightness (color) temperatures of 6000–24000 K, and electrical conductivities of 40–60000 (Ω·m)⁻¹. X-t diagram methods are used to estimate sound speeds of up to 5.5 km/s at pressures of 30–75 GPa. The optical absorption coefficients in the violet and red (30–300 cm⁻¹) are measured at pressures of 20–90 GPa from the rise in brightness of the shock front luminosity. The optical reflection coefficient of the shock front (∼13%) at a pressure of 76.1 GPa is measured for the first time. Zh. éksp. Teor. Fiz. 116, 551–562 (August 1999)