V. Ya. Ternovoi

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.

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.

Near-Critical-Point Thermodynamics from Shock Experiments with Porous Ni Samples

Results of experiments on the expansion of shock-compressed nickel samples into helium are presented. An isentrope with an initial pressure of 170 GPa was studied. The radiance temperature of the nickel sample and the velocity of the shock wave, generated in helium, were measured by a fast multichannel optical pyrometer; other parameters, such as the particle velocity, the pressure on the He-Ni interface, and the temperature of He were calculated using He Hugoniot (chemical plasma model). To increase the shock entropy up to a near-critical value and to intensify the process of heat-mass transfer, porous samples were used. Final states with pressures below 1.5 GPa, determined by the initial He pressure, were generated. The isobaric overheat of nickel by hot shocked helium provided an information about the nickel liquid spinodal. The change in slope of an isentrope in the pressure-particle velocity plane allowed an estimate of the point of its entrance in the two-phase region. Estimates of the critical temperature and pressure were made from peculiarities of P-T path, using various models of the nickel liquid spinodal to represent experimental data.

TWAC-ITEP proton microscopy facility

A proton radiography facility with the use of magnetic optics (PUMA proton microscope) has been developed at the TWAC-ITEP accelerator-accumulator facility (the ITEP terawatt accumulator) for measuring the substance density distribution inside static and dynamic objects using the proton beam with an energy of 800 MeV. The proton radiographic image of an object of investigation placed in the object plane of the setup is formed in the plane of the detector with magnification K = 4 with the aid of the magneto-optical system consisting of four quadrupole lenses on permanent magnets. The PUMA facility is intended for measuring objects with an areal density of up to 20 g/cm2 with a field of vision as large as 20 mm in diameter. The spatial resolution of radiographic images depends strongly on the areal density of the object of investigation. For the PUMA facility, the spatial resolution varies from 60 to 115 μm at an areal density of 0.46–17 g/cm2, respectively. The dynamical state of substance can be investigated in four consecutive radiographic images, since the time structure of the proton beam consists of four pulses, each with a duration of 47 ns (full width at half maximum (FWHM)) and an interval of 250 ns between them. This article is devoted to the description of the proton microscope construction. The main metrological characteristics of the facility are described using experiments with static and dynamic objects as an example.

Overview of warm-dense-matter experiments with intense heavy ion beams at gsi-darmstadt

This paper presents an overview of the warm-dense-matter physics experiments with intense heavy ion beams that has been carried out at the Gesellschaft fur Schwerionenforschung (GSI), Darmstadt, Germany. These experiments are a joint effort of GSI-Darmstadt, TU-Darmstadt, ITEP-Moscow, IPCP-Chernogolvka and LBNL-Berkeley. In the performed experiments, electron-cooled beam of 238U73+ ions with initial ion energy of 350 AMeV has been used. The intense, up to 2.5 - 109 ions/bunch, ion pulses have been compressed to 110 ns (FWHM) and focused at the target to a spot down to 150 mum diameter. The beam intensity and the pulse shape have been measured by current transformers installed in front of the target chamber whereas the upper limit for the focal spot size has been determined by recording beam-induced emission of argon gas at ionic spectral lines. It was shown that using intense heavy ion beam that is presently available at GSI and employing the HIHEX beam-target design concept, it is possible to investigate basic thermodynamic and transport properties of HED metal states in the two-phase liquid-gas region and near the critical point.

A study of near-critical states of metals in shock-wave experiments

Methods for creating near-critical states of the liquid-vapor phase transition during shock wave impact and optical methods for determining the positions of the boundaries of the two-phase region and the parameters of the critical point of the liquid-vapor phase transition (temperature, pressure) are described.

Jet formation in plasma compression in acute-angle geometry

Shock compression under acute-angle geometry is used with a metallic projectile [1-3] to produce a dense high-temperature plasma. The gas dynamics of the compression may be substantially affected by the interaction between the projectile and the walls of the container at the point of contact. Cumulative jets may be produced from the materials under certain conditions, which may contaminate the gas, produce inhomogeneity in the flow, and reduce the limiting parameters.