Yunjun Gu

Self-consistent variational calculation of the dense fluid helium in the region of partial ionization

Developments in shock-wave experimental techniques have allowed Megabar pressure range in dense fluid to be probed. It has been shown that the dissociation of the molecule and ionization of the atom become operative under such ultrahigh pressures. The dense fluid helium will be ionized in high pressures and temperatures. The ionization energy of helium will be lowered due to the interactions among all particles of He, He+, He2+, and e. The ionization degree is obtained from nonideal ionization equilibrium, taking into account the correlation contributions to the chemical potential which is determined self-consistently by the free energy function. The composition of dense helium can be calculated with given densities and temperatures. The equations of state of dense helium plasma are predicted in the density and temperature range of 0

Equation of state of partially ionized argon plasma

The ionization degree, Hugoniots, and equation of state of partially ionized argon plasma were calculated by using self-consistent fluid variational theory for temperature of 6–50 kK and density of 0.05–4.0u2009g/cm3. The corrections of lowering of ionization energy of fluid argon caused by the interactions among all particles of Ar, Ar+, Ar2+, and e have been taken into consideration in terms of the correlation contributions to the chemical potential which is determined self-consistently by the free energy function. The initial density effects of gas argon under shock compression have been discussed. Comparison is performed with available shock-wave experiments and other theoretical calculations.

Measurements of the principal Hugoniots of dense gaseous deuterium−helium mixtures: Combined multi-channel optical pyrometry, velocity interferometry, and streak optical pyrometry measurements

The accurate hydrodynamic description of an event or system that addresses the equations of state, phase transitions, dissociations, ionizations, and compressions, determines how materials respond to a wide range of physical environments. To understand dense matter behavior in extreme conditions requires the continual development of diagnostic methods for accurate measurements of the physical parameters. Here, we present a comprehensive diagnostic technique that comprises optical pyrometry, velocity interferometry, and time-resolved spectroscopy. This technique was applied to shock compression experiments of dense gaseous deuterium–helium mixtures driven via a two-stage light gas gun. The advantage of this approach lies in providing measurements of multiple physical parameters in a single experiment, such as light radiation histories, particle velocity profiles, and time-resolved spectra, which enables simultaneous measurements of shock velocity, particle velocity, pressure, density, and temperature and e...

Self-consistent fluid variational theory for the equation of state and dissociation of dense hydrogen and nitrogen

The self-consistent fluid variational theory (SFVT) is used to calculate the pressure dissociation of dense hydrogen and nitrogen at high temperatures. The accurate high-pressure and high-temperature effective pair potentials are adopted to describe the intermolecular interactions, which are made to consider molecular dissociation. This paper focuses on a mixture of atoms and molecules and is devoted to the study of the phenomenon of pressure dissociation at finite temperature. The equation of state and dissociation degree are calculated from the free energy functions in the temperature range 4000-15 000 K and density range 0.1-3.2 g cm -3 for dense nitrogen and in the temperature range 2000- 10 000 K and density range 0.02-1.0 g cm -3 for dense hydrogen, which can be compared with other approaches and experiments. The pressure dissociation is found to occur in the higher density range, while temperature dissociation is a more gradual effect.

Equation of state and transport properties of warm dense aluminum by ab initio and chemical model simulations

We have performed the ab initio molecular dynamics (AIMD) simulations for aluminum in the density and temperature range of 2.35–7.00u2009gu2009cm−3 and 1000–70u2009000u2009K, respectively. The equation-of-state data obtained from the AIMD simulations are consistent with the available experimental and theoretical results. The electrical conductivity and thermal conductivity obtained by combining the Kubo-Greenwood formula with the AIMD simulations are also in agreement with the available experimental and theoretical results. The electrical conductivity calculated by a linear mixing rule (LMR) in the chemical picture provides appropriate although relatively underestimated values compared to those based on AIMD simulation. Both LMR and AIMD simulations demonstrate that a metal to nonmetal transition takes place at a temperature less than 30u2009000u2009K. The thermal power calculated shows not the direct signal connecting with the metal-nonmetal transition. The coupling parameter, degeneracy parameter, and fractions of warm dense a...

First-principles study of conducting behavior of warm dense neon

The energy gap of solid neon increases with density, which is an opposite density dependency compared to other noble gases. In order to investigate whether this abnormal phenomenon survives in the warm dense region, where the conducting behavior is closely related to the energy gap, we calculated the electrical conductivity of fluid neon for temperatures of 103–105u2009K and densities of 1.50–10.0u2009g/cm3 with a first-principles method. Temperature and density dependencies of conductivity in this region were analyzed. The results indicate that the conducting behavior is sensitive to the temperature; there is a significant increase in the direct current (dc) conductivity from 10 000 to 20 000u2009K. Contrary to other noble gases, we found an abnormal density dependency of dc conductivity, which decreases with increasing density at a given temperature. This phenomenon is due to the elevating localization of electrons and the broadening of the energy gap based on the analyses of charge density distribution and electro...

Equation of state of dense neon and krypton plasmas in the partial ionization regime

The compression behaviors of dense neon and krypton plasmas over a wide pressure-temperature range are investigated by self-consistent fluid variational theory. The ionization degree and equation of state of dense neon and krypton are calculated in the density-temperature range of 0.01–10u2009g/cm3 and 4–50 kK. A region of thermodynamic instability is found which is related to the plasma phase transition. The calculated shock adiabat and principal Hugoniot of liquid krypton are in good agreement with available experimental data. The predicted results of shock-compressed liquid neon are presented, which provide a guide for dynamical experiments or numerical first-principle calculations aimed at studying the compression properties of liquid neon in the partial ionization regime.

The equation of state of dense xenon plasma under double-shock compression to 172 GPA

Warm dense plasmas having uniform, constant density, and temperature were generated by passage of planar shock wave through gas. The pressure of the Xe plasma was accurately measured by optical radiation method in the range of 172 GPa. The shock was produced using the flyer plate impact by accelerated up to ~6 km/s with a two-stage light gas gun. The time-resolved optical radiation histories were acquired by using a multi-wavelength channel optical transience radiance pyrometer. Shock velocity was measured and particle velocity was determined by the impedance-matching methods. Experimental data available of the Xe specimen in this region were compared with the calculations by the self-consistent fluid variational theory (SFVT). The observed shock compression ratios range from ρ/ρ0 = 3.7 for the initial density of 2.2 g/cm3 to ρ/ρ0 = 8.5 for the initial density of 0.04 g/cm3. The comparison of the Hugoniot in the Pressure-compression plane clearly shows how higher initial densities result in lower final co...

THE DISSOCIATION AND THERMODYNAMICS OF DENSE FLUID OXYGEN BY SELF‐CONSISTENT FLUID VARIATIONAL THEORY

The dissociation, pressure, internal energy, and entropy of dense fluid oxygen at high temperatures and densities have been calculated from the free‐energy functions using the self‐consistent fluid variational theory. The accurate high‐pressure and high‐temperature effective pair potentials are adopted to describe the intermolecular interactions, which are made to consider molecular dissociation. In this paper, we focused on a mixture of oxygen atoms and molecules and investigated the phenomenon of pressure dissociation at finite temperature. The single‐shock Hugoniot derived from this equation of state agrees well with gas‐gun experiments for pressure vs density. As density and pressure increase along the Hugoniot, the system appears to undergo a continuous transition from a molecular to a partially dissociated fluid containing a mixture of atoms and molecules. The equation of state and dissociation degree are predicted in the ranges of temperature of 5000–16u2009000 K and density of 0.1–4.5u2009g/cm3. These dat...