Results for the reflection coefficient of shock-compressed dense xenon plasmas at pressures of 1.6-20 GPa and temperatures around 30 000 K using laser beams of wavelengths 1.06 micro m and 0.694 micro m are presented, which indicate metallic behavior at high densities. For the theoretical description of the experiments, a quantum statistical approach to the dielectric function is used. The comparison with molecular dynamics simulations is discussed. We conclude that reflectivity measurements at different wavelengths can provide information about the density profile of the shock wave front.
The results of measurements of the Hall resistivity, static conductivity and reflectivity of nonideal plasma of argon and xenon are presented. The plasma was generated behind front of powerful shock waves with the help of explosively driven technique. In the experiments with the magnetic field the dense plasma was studied in the region of partial ionization at pressures of 30-650 MPa and temperatures of 6000-17000 K. The experiments on plasma reflectivity on the wave length 694 nm were performed at densities of 1-4 g/cc, pressures of 4-20 GPa and temperatures of 30000 K. The comparison of experimental results with different theoretical models of dense plasma is carried out.To measure Hall resistivity plasma was placed in the uniform magnetic field ∼5 T, which was produced inside a solenoid reeled on the explosive generator channel. Plasma was generated behind front of incident and reflected shock waves with the help of linear explosively driven tubes [1]. In present work the initial pressure and temperature of gas was P 0 = 0.4 MPa and T 0 = 300 K. The measurements were performed at P = 30-650 MPa, T = 6-17 kK, Coulomb coupling parameter Γ = 0.01-2.8. Electron density was calculated from measured values of Hall potential difference. Electrical conductivity measurements were carried out by four probes method [2]. Shock wave front velocity was measured by the electrocontact basis method.The comparison of experimental results with different models of thermodynamic and transport properties of nonideal xenon plasma is shown in figures 1-2. Where D is the velocity of incident shock wave, the lower groups of curves and dots correspond to incident wave, upper curves -reflected. The experimental data are represented in the graphs by quadrate symbols.The possibilities of calculation by approach 4 (figure 1) are restricted only by area of weakly non-ideal plasma. Arrows mark limit points, for which it was possible to carry out calculation using model 4. Measured values of electron density are in agreement with models 1,3 [3,4].In figure 2 the comparison of different transport models of the partially ionized plasma of Xe are given. Magnetic field was not taken into account in the expressions of electrical conductivity because of explored plasma was not magnetized. For calculation of thermodynamic parameters Debye approximation in grand canonical ensemble for Coulomb interaction was used [3,4].As it is seen from figure 2 the experimental results on conductivity are reasonably described only by Frost formula, the remaining methods yield overestimation of calculated data above experiment. Mutual positions of theoretical curves represented in figure 2 hold down for other thermodynamic models of dense xenon plasma also. The experiments with argon plasma carried out at shock front velocities D=2.4-3.4 km/s corresponded to weak coupling domain (Γ <1). Behavior of experimental and calculated electron density and conductivity for argon plasma were the same as for xenon. The comparison of measured values of conductivity and electron d...
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