W. J. Nellis

The equation of state of platinum to 660 GPa (6.6 Mbar)

Platinum metal was shock compressed to 660 GPa using a two‐stage light‐gas gun to qualify this material as an ultrahigh‐pressure standard for both dynamic and static experiments. The shock velocity data are consistent with most of the previously measured low‐pressure data, and an overall linear us−up relationship is found over the range 32–660 GPa. As a part of this work, we have also extended the Hugoniot of the tantalum standard we use to 560 GPa; we have included these data into a new linear fit of the tantalum Hugoniot between 55–560 GPa. We also present the results of a first‐principles theoretical treatment of compressed platinum. The fcc phase is predicted to remain stable to beyond 550 GPa. In addition, we have calculated the 300‐K pressure‐volume isotherm and the Hugoniot. The latter is in excellent agreement with experimental results and qualifies the former to at least 10% accuracy.

Shock compression of aluminum, copper, and tantalum

Hugoniot curves for Al (alloy 11000), Cu (type oxygen‐free high‐conductivity), and Ta have been measured in the shock pressure range 30–430 GPa (0.3–4.3 Mbar) with a two‐stage light‐gas gun. Impactor velocities were measured to 0.1% by flash radiography. Shock velocities were measured to 0.5–1.2% with an electronic detection system with subnanosecond time resolution. Our data and those of other workers were fitted to a linear relation between shock and mass velocities. The fractional standard deviations of the data from the fits range from 0.6 to 0.9% for the three metals. Methods of data analysis and error analysis for individual data points and for the least‐squares fitting to the data sets are presented. Bands of uncertainty about the fits, arising from experimental uncertainties in the data, are presented and are used to calculate the systematic error introduced by the method of shock‐impedance matching. The accuracy of the data and of the fits qualifies these metals as equation‐of‐state standards for...

Equation of state and electrical conductivity of water and ammonia shocked to the 100 GPa (1 Mbar) pressure range

Dynamic equation‐of‐state data for liquid H2O and NH3 were measured in the shock pressure range 30–230 GPa (0.3–2.3 Mbar) using a two‐stage light‐gas gun. Electrical conductivities of water were also measured in the shock pressure range 28–59 GPa (280–590 kbar). The experimental techniques to measure the electrical conductivity in a 50 ns time interval and to cool the target holders to liquid ammonia temperatures (230 K) are described. The H2O data are discussed in terms of the statistical mechanics model of Ree. At temperatures above 3000 K significant molecular ionization occurs.

The temperature of shock‐compressed water

Temperatures from 3300–5200 K were measured in liquid H2O shocked to 50–80 GPa (500–800 kbar). A six‐channel, time‐resolved optical pyrometer was used to perform the measurements. Good agreement with the data is obtained by calculating the temperature with a volume‐dependent Gruneisen parameter derived from double‐shock data and a heat capacity at constant volume of 8.7 R per mol of H2O.

Equation‐of‐state data for molecular hydrogen and deuterium at shock pressures in the range 2–76 GPa (20–760 kbar)a)

Dynamic equation‐of‐state data for D2 and H2 were measured in the pressure range 2–76 GPa (20–760 kbar) using a two‐state light‐gas gun. Liquid specimens were shocked from initial states near the saturation curve at 20 K. Maximum compression was sixfold over initial liquid density at a calculated temperature of 7000 K for D2. The data is discussed in terms of the theory of Ross et al., which includes an effective intermolecular pair potential, molecular vibration, free molecular rotation, and molecular dissociation.

Shock compression of liquid argon, nitrogen, and oxygen to 90 GPa (900 kbar)

Dynamic equation‐of‐state data for liquid Ar, N2, and O2 were measured in the shock pressure range 21–91 GPa (210–910 kbar) by means of a two‐stage light‐gas gun. The liquids were shocked from initial states near their saturation curves at 0.1 MPa (1 bar) and 80 K. The cryogenic target system is described. The initial liquid densities were obtained by measuring the temperature and pressure of the specimens and calculating the densities from published equations of state. Shock velocities were measured to 0.5–1.1% accuracy with an electronic detection system with subnanosecond time resolution. Impactor velocities in the range 4–7 km/s were measured to 0.1% accuracy with a flash radiographic technique. Mass velocities were obtained by the method of shock impedance matching. The data are discussed in terms of the statistical–mechanical theories of Ross and Ree.

Dynamic compression of materials: metallization of fluid hydrogen at high pressures

Dynamic high pressure is 1 GPa (10 kbar) or greater with a rise time and a duration ranging from 1 ps (10−12 s) to 1 µs (10−6 s). Today it is possible in a laboratory to achieve pressures dynamically up to ~500 GPa (5 Mbar) and greater, compressions as much as ~15-fold greater than initial density in the case of hydrogen and temperatures from ~0.1 up to several electronvolts (11 600 K). At these conditions materials are extremely condensed semiconductors or degenerate metals. Temperature can be tuned independently of pressure by a combination of shock and isentropic compression. As a result, new opportunities are now available in condensed matter physics at extreme conditions. The basic physics of the dynamic process, experimental methods of generating and diagnosing matter at these extreme conditions and a technique to recover metastable materials intact from ~100 GPa shock pressures are discussed.Results include (i) generation of pressure standards at static pressures up to ~200 GPa (2 Mbar) at 300 K, (ii) single-shock compression of small-molecular fluids, including resolution of the recent controversy over the correct shock-compression curve of liquid D2 at 100 GPa pressures, (iii) the first observations of metallization of fluid hydrogen, nitrogen and oxygen compressed quasi-isentropically at 100 GPa pressures, (iv) implications for the interiors of giant planets within our solar system, extrasolar giant planets and brown dwarfs discovered recently and the equation of state of deuterium–tritium in inertial confinement fusion (ICF) and (v) prospects of recovering novel materials from extreme conditions, such as metastable solid metallic hydrogen. Future research is suggested.

Shock compression of liquid carbon monoxide and methane to 90 GPa (900 kbar)

Dynamic equation‐of‐state data for liquid CO and CH4 were measured in the shock pressure range 5–92 GPa (50–920 kbar) using a two‐stage light‐gas gun. The liquids were shocked from initial states near their saturation curves at 77 and 111 K for CO and CH4, respectively. The experimental technique used to double‐shock CH4 is described. The CO data were examined by using three theoretical models: (1) a chemically nonreactive model, (2) a quasi‐chemical‐equilibrium model that allows CO to dissociate into gaseous species and graphite, and (3) a chemical‐equilibrium model that also includes a dense carbon phase which exists at higher pressures and temperatures than graphite. This dense phase is assumed to be diamond. Our analysis shows that at low pressure chemical equilibrium takes much longer than a typical shock passage time. As a consequence, the experimental data initially follow the nonreactive Hugoniot to pressures well beyond the chemical dissociation limit. Both the experimental data and the Hugoniot computed with case (3) agree satisfactorily at high pressure. Further consequences of these observations to high‐explosive studies are discussed. The theoretical analysis for the CH4 data was presented in an earlier paper.

The ruby pressure standard to 150 GPa

A determination of the ruby high-pressure scale is presented using all available appropriate measurements including our own. Calibration data extend to 150 GPa. A careful consideration of shock-wav ...

Diagnostic system of the Lawrence Livermore National Laboratory two-stage light-gas gun

A two‐stage light‐gas gun is used for a variety of dynamic physical‐property measurements at 100 GPa (1 Mbar) pressures. The diagnostic system described here consists of a flash x‐ray system to measure impactor velocity, detectors and electronics to measure shock‐wave velocities with subnanosecond resolution, and data–analysis techniques that permit us to measure the tilt and distortion of the impactor and of the resulting shock front. We describe our methods for safely purging hydrogen gas from the system after each shot.