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Beam-induced fluorescence of dense gas targets has been studied for its application to measure the transverse intensity distribution of energetic focused heavy ion beams. Mechanisms of light emission are discussed on the basis of measured wavelength- and time-resolved light emission of argon. Gas pressures from 10 mbar up to 1 bar have been used. Transverse beam intensity profiles of 200 – 400 AMeV 238U pulses from the heavy ion synchrotron SIS-18 at the Gesellschaft fur Schwerionenforschung, Darmstadt, Germany with up to 5 · 109 particles per pulse focused to a sub-millimeter spot have been recorded with argon and helium as target gases. Beam profiles recorded at the ArII lines by an optical filter resulted in the narrowest, most realistic beam diameters. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work release isentropes of shocked porous molybdenum were investigated. Samples with an initial porosity m = ρ0/ρ = 1.4 and 3.1 were studied to achieve near-critical entropy states of metal after shock compression. Compressed samples were expanded into helium with different initial pressures. The brightness temperature of the metal and the helium shock wave velocity were measured with a fast multichannel pyrometer. The helium shock wave velocity was used to determine the final pressure (P S) of expansion of the metal and the velocity of metal expansion (W S). Location of peculiarities on the P S–W S and P S–T P curves of the isentropes gives the location of their entrance into the two-phase region. Estimation of the molybdenum critical temperature and pressure was carried out on the basis of the experimental data.

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.

The problem of the nature of thermodynamic properties and the high level electrical conductivity of substances at high pressures and temperatures is one of the most key issues of physics of high energy densities. So called pressure ionization is one of the most impressive demonstrations of the strong coupling effects in plasma under compression. Noble gases are the simplest object of studying of these phenomena because of absence of molecules and spherical symmetry of their atoms. In the present paper we are trying to have a common look from the chemical plasma picture on the whole available massive of the experimental data on Ar and Xe in a wide range of the parameters: from gaseous densities of 0,01 g/cc and pressures of several kilobars up to extremely high densities corresponding to the insulator-metal transition and megabar pressure range. (orig.)

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.

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.

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.

The modified equation of state of helium‐hydrogen mixtures was used for 1D hydrodynamic simulation of performed experiments the multiple shock compression of Jupiter and Saturn model atmospheres. That permitted us to obtain the isentropic compression at third and later steps of compression in pressure region 20 –150 GPa. It was shown, that the helium‐hydrogen mixtures become conductive due to appearance of hydrogen conductance. The intervals of pressure — temperature — density states of these transitions are 30–50 GPa − 4400–5000 K − 0.4–0.5 g/cm3 for Jupiter and 60–80 GPa − 4600–4800 K − 0.53–0.6 g/cm3 for Saturn in accordance with our new and previous experiments with pure hydrogen and gas mixtures.

Physical properties of hot dense matter at megabar pressures are considered. The new experimental results on pressure ionization of hot matter generated by multiple shock compression of hydrogen and noble gases are presented. The low‐frequency electrical conductivity of shock compressed hydrogen, helium and xenon plasmas was measured in the megabar range of pressures. To reduce effects of irreversible heating and to implement a quasi‐isentropic regime strongly compressed matter was generated by the method of multiple shock compression in planar and cylindrical geometries. As a result, plasma states at pressures of the megabar range were realized, where the electron concentration could be as high ne ∼ 2×1023 cM −3, which may correspond to either a degenerate or a Boltzmann plasma characterized by a strong Coulomb and a strong inter‐atomic interaction. A sharp increase (by three to five orders of magnitude) in the electrical conductivity of a strongly nonideal plasma due to pressure ionization was recorded, and theoretical models were invoked to describe this increase. Opposite effect was observed for lithium compressed by multiple shock up to pressures ∼ 200 GPa, where electrical conductivity was sharply decreased as pressure increased.

In this work release isentropes of shocked porous molybdenum were investigated. Samples with initial porosity m=ρ0/ρ=1.4; 3.1 were used to achieve near‐critical entropy states of metal after shock compression. Shocked samples were expanding into helium with different initial pressures. The brightness temperature (TP) of metal and the velocity of shock wave in helium were measured by fast optical pyrometer. Shock wave velocity value allowed to determine the final pressure (PS) of expansion of metal and the velocity of metal expansion (WS). Location of peculiarities on isentropes in PS‐WS and PS‐TP diagrams gives the location of their entrance into two‐phase region. Estimation of molybdenum critical temperature and pressure were done on the basis of experimental data.

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 n(e) approximate to 2 x 10(23) cm(-3), which may correspond to either a degenerate or a Boltzmann plasma characterized by a strong Coulomb (Gamma(D) = 1-10) and a strong interatomic (Gamma(a) = r(a)n(a)(1/3) similar to 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. (C) 2003 MAIK "Nauka / Interperiodica".

Near critical point states of tin were generated by the expansion of shocked metal into helium to pressures of several kbars and less. Thermodynamic states on release isentropes originated from shock pressures of 137, 180, and 220 GPa were investigated. Gas dynamic parameters and temperature have been measured by the use of the method of optical pyrometry. The heating of tin on the boundary with shocked gas was described due to the difference between tin and gas temperatures. The problem of the interface heat transfer was solved to obtain the temperature of expanded tin. The point of intersection of experimental and theoretical curves for maximum overheat temperatures was used to estimate parameters of the critical point, which occurred at Pcrit=0.25 GPa, Tcrit=7850 K (dT=300K, dP=0.02 GPa). The result is in a good agreement with available evaluations of the critical point. Experimental data obtained have been used for construction of multi-phase wide-range equation of state for tin.

The conductivity of cooled gaseous hydrogen with initial density 0,022g/cc was measured inside the single-crystal sapphire cell. The transition of hydrogen to a high electroconducting state during the fourth circulation of the shock wave (40–50 GPa) was registered. It has been concluded that the behaviour of brittle substances, (e.g. sapphire) used as isolators, should be taken into account to interpret the dielectric-metal transition in low initial density substances.

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.