X-ray scattering measurements on imploding CH spheres at the National Ignition Facility

We have performed spectrally resolved x-ray scattering measurements on highly compressed polystyrene at pressures of several tens of TPa (100 Mbar) created by spherically convergent shocks at the National Ignition Facility. Scattering data of line radiation at 9.0 keV were recorded from the dense plasma shortly after shock coalescence. Accounting for spatial gradients, opacity effects, and source broadening, we demonstrate the sensitivity of the elastic scattering component to carbon $K$-shell ionization while at the same time constraining the temperature of the dense plasma. For six times compressed polystyrene, we find an average temperature of 86 eV and carbon ionization state of 4.9, indicating that widely used ionization models need revision in order to be suitable for the extreme states of matter tested in our experiment.

Figure 1

Experimental setup of the Gbar EOS fundamental science experiments.

Figure 2

Post-experiment simulations of the radial profiles of the basic plasma parameters as obtained from the radiation-hydrodynamics code hydra 480 ps after shock stagnation.

Figure 3

Comparison of experimental data with synthetic scattering spectra using the full 3D ray-tracing and weighting scheme.

Figure 4

Comparison of the 0D fit results with Thomas-Fermi and Stewart-Pyatt predictions for the carbon ionization when varying density and temperature.

Figure 5

Ionization degree of the carbon component predicted by various models for radial density and temperature profiles calculated by HYDRA simulations at the time of probing. The short lines on the right are the predictions for the average conditions in the sample. The gray shaded area gives the best fit to the experiment with error bars in the vertical direction. The gray scale in the horizontal direction indicates the weight $r^2\rho \left(r\right)$ of this radial region.