Frequency-dependent reflectivity of shock-compressed xenon plasmas

Abstract

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.

Opacity and conductivity measurements in noble gases at conditions of planetary and stellar interiors

“…S7). High reflectivity (>1%) and conductivity (>100 S/cm) occur above the dotted black line (12,23,30). Colored lines are conditions of He atmospheres of white dwarfs (9, 30) (green; for effective temperatures 8.0 and 4.5 kK) and He rain in planetary gaseous envelopes (blue and brown) (6,7,25,30) with thicker areas indicating predicted upper limit of He-H immiscibility (3,4).…”

“…Ne is predicted to have the highest metallization pressure of all known materials-10 3 times that of Xe and 10 times that of He (14,18,20,21)-and has never been documented outside of its insulating state. Experimental probes of extreme densities and temperatures in noble gases have previously relied on dynamic compression by shock waves (12,13,17,(22)(23)(24). However, in such adiabatic experiments, light and compressible noble gases heat up significantly and can ultimately reach density maxima (12,13,17,21,24,25), so that conditions created often lie far from those deep within planets (7,8) and stars (9).…”

Two‐moment modelling of the dynamic longitudinal conductivity of strongly coupled Coulomb systems

“…[32] we find numerical results for the internal and external conductivities in the longwavelength limiting case, obtained from MD simulations of a xenon plasma for the same thermodynamic conditions as in the first measurement of [29,30]. As we can see in Figs.…”

“…[8,28] and [29,30], we find the results of experimental measurements of reflectivity for dense shockcompressed xenon plasmas at pressures 1.6 ÷ 20 GP a and temperatures around 30 kK using laser beams with wavelengths 1.060 µm and 0.694 µm, respectively.…”

“…where the dielectric function can be written as Experimental data Two-moment model In Table 1 the experimental results on the reflectivity, according to [8,28] and [29,30], are compared to our fit with the varying model parameter ζ of (17) to reproduce the reflectivity data quantitatively. In particular, for the last points in both sets of measurements, for 16.7 GP a and 20.0 GP a, we can see that it is impossible to get the value of 0.47 and 0.43, respectively, since the maximum of the function occurs at 0.43 (log 10 (ζ) = −0.460) for the first case, and at 0.35 for the second one, though at these points the curve which shows the reflectivity as a function of ζ is quite flat in both cases.…”