S. V. Kvitov

THERMODYNAMIC PROPERTIES AND ELECTRICAL CONDUCTIVITY OF HYDROGEN UNDER MULTIPLE SHOCK COMPRESSION TO 150 GPA

Abstract The results of experiments on simultaneous registration of optical emission intensity and electrical resistivity of hydrogen layer at a multiple shock compression to pressure 106, 123 and 150 GPa are presented. The experimentally determined thermodynamic parameters of hydrogen at the first steps of compression are consistent with results of a semi-empirical equation of state for molecular hydrogen. Hydrogen electrical conductivity was traced from 0.1 to 1000 1 /( Ω cm ) under various regimes of compression and subsequent expansion.

Electrical conductivity of nonideal hydrogen plasma at megabar dynamic pressures

The electrical conductivity of a nonideal hydrogen plasma is measured under shock-wave compression to pressures ∼1.5 Mbar. It is found that the conductivity increases sharply (by five orders of magnitude) at a density ρ∼0.3−0.4 g/cm3, reaching close to liquid-metal values ∼103 S/cm. The data obtained can be described by a nonideal-plasma model taking into account the increase in the number of conduction electrons as a result of “ionization by pressure.”

Experimental determination of the conditions for the transition of Jupiter’s atmosphere to the conducting state

The intensity of optical radiation and resistance of a hydrogen-helium layer with He mass fraction Y=mHe/(mHe+mH)≅0.24, which corresponds to the composition of the outer layers of Jupiter’s atmosphere [2], were simultaneously measured under multiple shock compression up to 164 GPa in plane geometry. The initial pressure and temperature of the mixture were equal to 8 MPa and 77.4 K, respectively, and the velocity of steel strikers was equal to 6.2 km/s. These conditions allowed the generation of the final compressed curve close to the adiabatic states of Jupiter’s atmosphere according to the models proposed in [2, 3]. The conditions for the appearance of the conducting phase in the compression process and the achieved level of electrical conductivity were determined. The experimental data were compared with the one-dimensional fluid-dynamic simulation of the compression process using the equation of state for the mixture in a model similar to the one proposed in [3, 8]. The experimental data were also compared with the behavior of pure components having the same initial density as in the mixture and compressed to the same final pressure.

Liquid-vapor phase boundaries determination by dynamic experimental method

Shock-induced vaporization of matter under expansion from high energy states is of interest as an experimental method to determine two-phase region boundaries and position of critical point of liquid-vapor transition. High speed of expansion of matter on the boundary leads to formation of the so-called “boiling wave.” Intensive heat and mass transfer with hot shocked helium on the boundary give the opportunity to investigate states not only near binodal but also liquid spinodal. Another possibility to achieve near critical point pressures and temperatures is the heating of material by hot driving plasma under launching. This additional heating gives the possibility to achieve temperatures and pressures exceeding critical parameters of tungsten—one of the most refractory metals. New experimental results and issues of such investigation with nickel and tungsten is analyzed in the proposed paper.

Experimental study of lead critical point parameters

Two isentropes from lead shock states of 223 and 265 GPa have been traced in the pressure region below 0.6 GPa. Residual temperature and velocity of expansion into helium had been measured by optical pyrometry technique [1]. Fast heating of matter under investigation by shocked helium atmosphere was observed. Maximal overheat temperatures of liquid lead have been connected to ones of liquid spinodal. The experimental data were compared with the results of lead semiempiric wide-range equation of state [2]. It is proved, that critical point pressure was less then predicted nowadays, and critical point temperature in the range of uncertainties is the same in the framework of van-der-Waals model.

SiO2-aerogel plasma properties in the energy range up to 65 kJ/g

We present a new data on pyrometry measurements of SiO2-aerogel under shock loading. Optically transparent samples with initial densities 0.36, 0.27 and 0.008 g/cc was shocked up to 65 kJ/g total energy of schock compression; temperatures up to 25000 K was measured. The analysis of data is described.

Temperature measurements and hydrogen transformation under dynamic compression up to 150 GPA.

Lithium fluoride single crystal window was used for optical light emission registration during quasi-isentropic compression of hydrogen to the pressures 100-150 GPa. Initially gaseous hydrogen samples at 78 K temperature and different pressures in the range 3-30 MPa were investigated. Recorded brightness temperature profiles in near infrared range of wavelength were analyzed to evaluate optical and transport properties of the investigated hydrogen sample and window. Two EOS models of hydrogen, with and without metallic region were used for 1-D simulation of its properties under dynamic compression and estimation of hydrogen temperature within compressed layer. The obtained data demonstrate abrupt change of final temperatures after heating higher then 3500K.

OPTICAL PROPERTIES OF DENSE PLASMA IN SHOCK AND RAREFACTION WAVES

Results of the experiments on measurements of optical properties of strongly coupled hot plasmas are presented. The fast optical pyrometry enabled us to obtain information on the thermodynamic and optical properties of condensed matter in the supercritical region of parameters and in the vicinity of the saturation curve. The experimental information is compared with the wide-range semiempirical equation of states and optical models of plasma.

CONDUCTIVITY OF MULTIPLE SHOCK COMPRESSED HYDROGEN ALONG 135 AND 180 GPA ISOBARS

The results of temperature and conductivity measurements of hydrogen, multiple shock compressed to the pressures 135 and 180 GPa are presented. Explosively driven steel plate with velocity up to 8 km/s was used for shock wave generation. Hydrogen with various initial pressures and temperatures was multiple shock compressed between steel bottom and sapphire window. Brightness temperature of hydrogen was measured by fast optical pyrometer. Electrical resistance of shocked hydrogen was measured simultaneously with optical pyrometer records. The conductivity of hydrogen decreased from 424 1/Om/cm at 2700 K down to 20 1/Om/cm at 6000 K along 135 GPa isobar. The conductivity of hydrogen decreased from 800 1/Om/cm at 5000 K down to 100 1/Om/cm at 6700 K along 180 GPa isobar. Experimental results are compared with various theoretical predictions.

INVESTIGATION OF NEAR CRITICAL POINT STATES OF LITHIUM, SODIUM AND ALUMINIUM BY PULSE HEATING DURING LAUNCHING

The results of experimental investigation of near—critical point states of liquid‐vapour phase transition of of lithium, sodium and aluminium are presented. The metal foil samples were launched by explosively driven steel plate in Helium atmosphere; Li and Na—by direct impact and Al—by impact through the layer of helium. The heating of the Li and Na foils were performed by heat exchange with shocked He layer from the free side of sample; Al—by heating by multiple‐shocked He from the back side of the foil. The temperature of sample surface was measured by fast multi‐channel optical pyrometer. For Li and Na experiments the pressure was obtained from measured shock velocity in helium using base length technique; the 1‐D simulation of the process of launching was performed to obtain pressure for Al experiments. The obtained experimental information allowed to evaluate liquid spinodal line, and the position of critical points on pressure—temperature plane for investigated metals.