X-ray Thomson Scattering from Dense Plasmas

X-ray Thomson scattering has been developed for accurate measurements of densities and temperatures in dense plasmas. Experiments with laser-produced x-ray sources have demonstrated Compton scattering and plasmon scattering from isochorically-heated solid-density beryllium plasmas. In these studies, the Ly-alpha or He-alpha radiation from nanosecond laser plasmas has been applied at moderate x-ray energies of E = 3 - 9 keV sufficient to penetrate through the dense plasma and to avoid intense bremsstrahlung radiation at lower energies. In backscattering geometry, the experiments have accessed the non-collective Compton scattering regime where the spectrum reflects the electron velocity distribution of the plasma, thus providing an accurate measurement of the temperature. In addition to the inelastic Compton scattering feature, the spectra also show elastic (Rayleigh) scattering from tightly bound electrons. The intensity ratio of these features yields the ionization state that has been applied to infer the electron density in isochorically-heated matter. Forward scattering in these conditions have observed plasmons that allow direct and accurate measurements of the electron density from the frequency shift of the plasmon peak from the incident probe energy. The back and forward scattering data are in mutual agreement indicating an electron density of ne = 3 x 1023 cm-3, which is also consistent with results from radiation hydrodynamic simulations. These findings indicate that x-ray Thomson scattering provides accurate characterization in the previously unexplored regime of high-energy density matter. Future work will explore applications to measure compressibility, collisions, and electronic properties of dense matter