V. K. Gryaznov

Pressure-produced ionization of nonideal plasma in a megabar range of dynamic pressures

The low-frequency electrical conductivity of strongly nonideal hydrogen, helium, and xenon plasmas was measured in the megabar range of pressures. The plasmas in question were generated by the method of multiple shock compression in planar and cylindrical geometries, whereby it was possible to reduce effects of irreversible heating and to implement a quasi-isentropic regime. As a result, plasma states at pressures in the megabar range were realized, where the electron concentration could be as high as ne≈2×023 cm−3, which may correspond to either a degenerate or a Boltzmann plasma characterized by a strong Coulomb ΓD=1–10) and a strong interatomic Γa=rana1/3∼1) interaction. A sharp increase (by three to five orders of magnitude) in the electrical conductivity of a strongly nonideal plasma due to pressure-produced ionization was recorded, and theoretical models were invoked to describe this increase. Experimental data available in this region and theoretical models proposed by various authors are analyzed. The possibility of a first-order “phase transition” in a strongly nonideal plasma is indicated.

Experimental measurements of the compressibility, temperature, and light absorption in dense shock-compressed gaseous deuterium

Experimental data on the shock compression, temperature, and absorptivity of gaseous deuterium with an initial density close to its value in the liquid state were obtained on a spherical explosion shock-wave generator in a pressure range of 80–90 GPa. The obtained results are compared with the existing experimental and theoretical data.

Solar plasma: calculation of thermodynamic functions and equation of state

Calculations of thermodynamic properties for the solar plasma are presented. Effects of Coulomb interaction, exchange and diffraction effects, free electron degeneracy, relativistic corrections and radiation pressure contributions are taken into account. Calculations of the equation of state of the solar plasma with different element compositions are carried out. The contribution of various plasma effects and chemical element abundance to thermodynamic functions and in particular ?1 is discussed.

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 P0 = 267 atm and the temperature T0 = 10.5°C. Under such conditions, the plasma is strongly nonideal (Γ ∼ 450) with the degenerate (nλe3 ∼ 280) electron component and with an electron density of about 2.8 × 1023 cm−3.

Measurements of the electron concentration and conductivity of a partially ionized inert gas plasma

The results are presented of experiments performed to measure the electron concentration and conductivity of a partially ionized inert gas plasma in a magnetic field. The plasma was generated behind the front of incident and reflected shock waves excited by explosively driven linear generators. A magnetic field of about 5 T was formed inside a solenoid wound on the generator channel. Measurements were taken at P=30−650 MPa, T=6000−17000 K, and a Coulomb nonideality parameter of 0.01–2.8. Electron concentrations calculated from measured Hall voltages reached 1.6×1021 cm−3. The recorded conductivities were in the range 0.1–200 Ω −1 cm−1. The experimental results were compared with various models of the thermodynamic and transport properties of a nonideal plasma.

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 100–500 GPa. A thermodynamic model that satisfactorily describes the behavior of strongly compressed helium in a wide range of compression parameters has been proposed.

Hydrogen and deuterium in shock wave experiments, ab initio simulations and chemical picture modeling

We present equation of state data of shock compressed hydrogen and deuterium. These have been calculated in the physical picture by using ab initio molecular dynamics simulations based on finite temperature density functional theory as well as in the chemical picture via the Saha-D model. The results are compared in detail with data of shock wave experiments obtained for condensed and gaseous precompressed hydrogen and deuterium targets in a wide range of shock compressions from low pressures up to megabars.

Analysis of the presence of small admixtures of heavy elements in the solar plasma by using the SAHA-S equation of state

The thermodynamic functions of a weakly nonideal plasma are extensively calculated for conditions typical of the depths of stars by using the SAHA-S equation of state. These calculations ensure precise analysis of the effect of the heavy-element content on adiabatic compressibility in the depths of the Sun. Comparison of model calculations with recent helioseismic data ensures more precise determination of solar-plasma composition. This comparison shows that the inclusion of additional components to the composition of heavy-element admixtures is a necessary condition for the theoretical equation of state and the results of analysis of solar oscillations to be consistent.

Quasi-isentropic compressibility of a strongly nonideal deuterium plasma at pressures of up to 5500 GPa: Nonideality and degeneracy effects

We report on the experimental results on the quasi-isentropic compressibility of a strongly nonideal deuterium plasma that have been obtained on setups of cylindrical and spherical geometries in the pressure range of up to P ≈ 5500 GPa. We describe the characteristics of experimental setups, as well as the methods for the diagnostics and interpretation of the experimental results. The trajectory of metal shells that compress the deuterium plasma was detected using powerful pulsed X-ray sources with a maximal electron energy of up to 60 MeV. The values of the plasma density, which varied from ρ ≈ 0.8 g/cm3 to ρ ≈ 6 g/cm3, which corresponds to pressure P ≈ 5500 GPa (55 Mbar), were determined from the measured value of the shell radius at the instant that it was stopped. The pressure of the compressed plasma was determined using gasdynamic calculations taking into account the actual characteristics of the experimental setups. We have obtained a strongly compressed deuterium plasma in which electron degeneracy effects under the conditions of strong interparticle interaction are significant. The experimental results have been compared with the theoretical models of a strongly nonideal partly degenerate plasma. We have obtained experimental confirmation of the plasma phase transition in the pressure range near 150 GPa (1.5 Mbar), which is in keeping with the conclusion concerning anomaly in the compressibility of the deuterium plasma drawn in [1].

Measurement of density, temperature, and electrical conductivity of a shock-compressed nonideal nitrogen plasma in the megabar pressure range

Kinematic and thermodynamic parameters of shock-compressed liquid nitrogen are measured behind the front of a plane shock wave using plane wave and hemispherical shock wave generators. In these experiments, high values of compression parameters (shock-compressed hydrogen density? ≈ 3.25 g/cm3 and temperature T≈ 56000 K at a pressure of P ≈ 265 GPa) are attained. The density, pressure, temperature, and electrical conductivity of the nonideal plasma of shock-compressed liquid nitrogen are measured. A nearly isochoric behavior of the nitrogen shock adiabat is observed in the pressure range P = 100–300 GPa. The thermodynamics of shock-compressed nitrogen is an alyzed using the model of the equation of state in the quasi-chemical representation (SAHA code) as well as the semiempirical wide-range equation of state developed at the Institute of Experimental Physics. Experimental results are interpreted on the basis of calculations as the fixation of the boundary of transition of shock-compressed nitrogen from the polymer phase to the state of a strongly nonideal plasma at P ≈ 100 GPa, ? ≈ 3.4 g/cm3.