X-ray Thomson scattering in high energy density plasmas

TLDR

X‑ray Thomson scattering techniques have been developed to probe hot, dense plasmas at solid‑density electron concentrations, linking measured spectra to dielectric functions and structure factors that describe their physical properties. The paper seeks to advance laser‑based narrow‑band x‑ray sources and facilities to enable Thomson scattering experiments across inertial confinement fusion, radiation hydrodynamics, material science, and laboratory astrophysics. The authors use laser‑based narrow‑band x‑ray sources to obtain spectrally resolved Thomson scattering data from dense plasmas. Backscattering provides precise temperature, density, and ionization diagnostics via Compton scattering, while forward scattering reveals plasmon oscillations and offers direct measurements of collisions and quantum effects, enabling picosecond‑resolution compression and heating measurements in radiation‑heated and shock‑compressed plasmas.

Abstract

Accurate x-ray scattering techniques to measure the physical properties of dense plasmas have been developed for applications in high energy density physics. This class of experiments produces short-lived hot dense states of matter with electron densities in the range of solid density and higher where powerful penetrating x-ray sources have become available for probing. Experiments have employed laser-based x-ray sources that provide sufficient photon numbers in narrow bandwidth spectral lines, allowing spectrally resolved x-ray scattering measurements from these plasmas. The backscattering spectrum accesses the noncollective Compton scattering regime which provides accurate diagnostic information on the temperature, density, and ionization state. The forward scattering spectrum has been shown to measure the collective plasmon oscillations. Besides extracting the standard plasma parameters, density and temperature, forward scattering yields new observables such as a direct measure of collisions and quantum effects. Dense matter theory relates scattering spectra with the dielectric function and structure factors that determine the physical properties of matter. Applications to radiation-heated and shock-compressed matter have demonstrated accurate measurements of compression and heating with up to picosecond temporal resolution. The ongoing development of suitable x-ray sources and facilities will enable experiments in a wide range of research areas including inertial confinement fusion, radiation hydrodynamics, material science, or laboratory astrophysics.