Measurement of Short-Range Correlations in Shock-Compressed Plastic by Short-Pulse X-Ray Scattering

We have performed short-pulse x-ray scattering measurements on laser-driven shock-compressed plastic samples in the warm dense matter regime, providing instantaneous snapshots of the system evolution. Time-resolved and angularly resolved scattered spectra sensitive to the correlation effects in the plasma show the appearance of short-range order within a few interionic separations. Comparison with radiation-hydrodynamic simulations indicates that the shocked plastic is compressed with a temperature of a few electron volts. These results are important for the understanding of the thermodynamic behavior of strongly correlated matter for conditions relevant to both laboratory astrophysics and inertial confinement fusion research.

Figure 1

Experimental setup. (a) Target assembly and beams layout; (b) Au x-ray collimator with Cu backlighter foil; (c) wide angle spectrometer with HOPG crystal and image plate; (d) example of experimental spectra. The Cu calibration shot was taken by replacing the target assembly with a single copper foil. It is used for spectral and angular calibration of the data.

Figure 2

Radiative-hydrodynamics simulation. The rectangular areas represent the probed region of the sample for the two experimental shots discussed in the text. The height of the rectangles (temporal resolution) is exaggerated for clarity. The laser drive illuminates the target from the right side of the figure starting at $t=t_0$. Only plastic cells are shown in the plot.

Figure 3

Experimental data points and simulated spectra for $t=t_0+2\mathrm{ns}$ (upper panel) and $t=t_0+8\mathrm{ns}$ (lower panel). The coupling parameter is ${\Gamma }_{ii}=7.9$ for $t=t_0+2\mathrm{ns}$ and ${\Gamma }_{ii}=14.7$ for $t=t_0+8\mathrm{ns}$. SOCP and Debye-Hückel (DH) models are described in the text. Error bars represent the root mean square noise level in the recorded data.

Figure 4

Comparison between single-component and multicomponent HNC calculations for $S_{ii}(k)$. The plasma conditions refer to the case $t=t_0+8\mathrm{ns}$. The OCP calculations neglect screening, while $Y$-labeled lines use linear screening.