With the advent of high-energy-density (HED) experimental facilities, such as high-energy lasers and fast Z-pinch, pulsed-power facilities, millimeter-scale quantities of matter can be placed in extreme states of density, temperature, and/or velocity. This has enabled the emergence of a new class of experimental science, HED laboratory astrophysics, wherein the properties of matter and the processes that occur under extreme astrophysical conditions can be examined in the laboratory. Areas particularly suitable to this class of experimental astrophysics include the study of opacities relevant to stellar interiors, equations of state relevant to planetary interiors, strong shock-driven nonlinear hydrodynamics and radiative dynamics relevant to supernova explosions and subsequent evolution, protostellar jets and high Mach number flows, radiatively driven molecular clouds and nonlinear photoevaporation front dynamics, and photoionized plasmas relevant to accretion disks around compact objects such as black holes and neutron stars.

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Experimental astrophysics with high power lasers and Z pinches

▪ Abstract We know that giant planets played a crucial role in the making of our Solar System. The discovery of giant planets orbiting other stars is a formidable opportunity to learn more about these objects, what their composition is, how various processes influence their structure and evolution, and most importantly how they form. Jupiter, Saturn, Uranus, and Neptune can be studied in detail, mostly from close spacecraft flybys. We can infer that they are all enriched in heavy elements compared to the Sun, with the relative global enrichments increasing with distance to the Sun. We can also infer that they possess dense cores of varied masses. The intercomparison of presently characterized extrasolar giant planets shows that they are also mainly made of hydrogen and helium, but that they either have significantly different amounts of heavy elements, have had different orbital evolutions, or both. Hence, many questions remain and need to be answered to make significant progress on the origins of planets...

THE INTERIORS OF GIANT PLANETS: Models and Outstanding Questions

Hydrogen and helium are the most abundant elements in the Universe. They are also, in principle, the most simple. Nonetheless, they display remarkable properties under extreme conditions of pressure and temperature that have fascinated theoreticians and experimentalists for over a century. Advances in computational methods have made it possible to elucidate ever more of their properties. Some of these methods that have been applied in recent years, in particular, those that perform simulations directly from the physical picture of electrons and ions, such as density functional theory and quantum Monte Carlo are reviewed. The predictions from such methods as applied to the phase diagram of hydrogen, with particular focus on the solid phases and the liquid-liquid transition are discussed. The predictions of ordered quantum states, including the possibilities of a low- or zero-temperature quantum fluid and high-temperature superconductivity are also considered. Finally, pure helium and hydrogen-helium mixtures, the latter which has particular relevance to planetary physics, are discussed.

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The properties of hydrogen and helium under extreme conditions

Recently, deuterium has been the focus of a high level of experimental and theoretical activity, sparked by a disagreement on the experimental value of the maximum compression along the principal Hugoniot. The behavior of deuterium at megabar pressures is not well understood. It is of great interest to understand how the current uncertainty on the hydrogen/deuterium equation of state (EOS) affects the inferred structures of Jupiter and Saturn. In particular, the mass of a core of heavy elements (other than H and He) and the total mass of those heavy elements in these two planets are quite sensitive to the EOS of hydrogen and constitute important clues to their formation process. We present a study of the range of structures allowed for Jupiter and Saturn by the current uncertainty in the hydrogen EOS and astrophysical observations of the two planets. An improved experimental understanding of hydrogen at megabar pressures and better determinations of the gravitational moments of both planets are necessary to put tight bounds on their internal structure.

https://iopscience.iop.org/article/10.1086/421257/pdf

Shock Compression of Deuterium and the Interiors of Jupiter and Saturn

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The Properties of Hydrogen and Helium Under Extreme Conditions

Hugoniot points of liquid ${\mathrm{D}}_{2}$ were measured at shock pressures of 107, 54, and $28\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ using converging explosively driven systems (CSs). The two data sets measured with a laser $(L)$ and pulsed currents (PCs) differ substantially. Our results are in excellent agreement with the PC data and the error bars of the CS-PC data are less than half those of the $L$ data. The limiting compression obtained from the best fit to the CS-PC data is $4.30\ifmmode\pm\else\textpm\fi{}0.10$ at $100\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. The CS-PC data are in good agreement with path integral Monte Carlo and density functional theory calculations, which is expected to be the case at even higher shock temperatures and pressures, as well.

Shock compression of liquid deuterium up to 109 GPa

Experimental data on the compression of solid deuterium at a pressure of ∼60 GPa are presented. The data were obtained on a generator of powerful converging spherical shock waves. The results are compared with the data of shock experiments obtained on a Nova laser facility and an electrodynamic EPBF-Z plant.

Shock compression of solid deuterium

The experimental data on the shock compression of liquid nitrogen in the megabar pressure range are reported. The experiments have been performed with a spherical measuring setup in which pressure is created by the impact of a steel shell accelerated to a velocity of 23 km/s on the samples. The density of shock-compressed nitrogen at a pressure of about 320 GPa is about 3.4 g/cm3 (compression degree of about 4.2). The experimental data are described using a model equation of state.

Shock compression of liquid nitrogen at a pressure of 320 GPa

The results of experiments on determining the shock-wave compression of initially solid hydrogen (protium) in the pressure range from 17 to 66 GPa are reported. The data have been obtained by using spherical explosive charges. Pressure in samples is created by the impact of a steel striker accelerated to maximum velocities of 23 km/s. Gaseous protium is converted to the solid state using a special cryogenic cooling system.

Shock-Wave Compression of Hydrogen to Pressures of 65 GPa

We describe the experimental setup, as well as results and analysis of experiments on isothermal compression of stable hydrogen isotopes, viz., protium (H2) and deuterium (D2), in the initial (at P0 = 0.1 MPa) solid state up to pressure of 550 GPa using facilities based on a magnetocumulative generator and an X-ray diffraction complex including a betatron and an X-ray image recording system. We consider the points obtained on the “cold” isentrope (T0 = 5–13 K) for protium and deuterium. The results are compared with those obtained using static and other dynamic facilities, as well as with the results of various calculations.

G.V. Boriskov

Papers

Shock compression of liquid deuterium up to 109 GPa

Shock compression of solid deuterium

Shock compression of liquid nitrogen at a pressure of 320 GPa

Shock-Wave Compression of Hydrogen to Pressures of 65 GPa

Analysis of Zero-Point Isotherm of Hydrogen Isotopes in the Ultrahigh Pressure Range