X-ray Thomson Scattering as a high-precision tool for Warm Dense Matter diagnostics

Warm dense matter (WDM)---an extreme state that is characterized by extreme densities and
temperatures---has emerged as one of the most active frontiers in plasma physics and material
science. In nature, WDM occurs in astrophysical objects such as giant planet interiors and brown
dwarfs. In addition, WDM is highly important for cutting-edge technological applications such as
inertial confinement fusion and the discovery of novel materials. In the laboratory, WDM is studied
experimentally in large facilities around the globe, and new techniques have facilitated
unprecedented insights. Yet, the interpretation of these experiments requires a reliable diagnostics
based on accurate theoretical modeling, which is a notoriously difficult task [1].

In this talk, I will explain how we can use X-ray Thomson scattering (XRTS) measurements [2] to infer important system parameters such as the temperature, density, and degree of ionization. Interestingly, standard forward modeling methods based on the widespread Chihara decomposition have neglected transitions between free and bound electrons (the inverse process of the usual bound-free transitions), which are negligible at ambient conditions, but become important in the WDM regime [3]. In addition, I will show how switching to the imaginary-time representation opens up new avenues towards the model-free interpretation of XRTS signals, and gives one direct access to the temperature [4,5] and electronic correlations [6] of the system. Finally, I will outline new PIMC capabilities [7,8] that allow for quasi-exact simulations of experiments conducted at the Gbar platform at the National Ignition Facility (NIF) in Livermore.

[1] M. Bonitz et al, Physics of Plasmas 27, 042710 (2020)
[2] S. Glenzer and R. Redmer, Reviews of Modern Physics 81, 1625 (2009)
[3] M. Böhme et al, arXiv:2306.17653 (submitted)
[4] T. Dornheim et al, Nature Communications 13, 7911 (2022)
[5] T. Dornheim et al, Physics of Plasmas 30, 042707 (2023)
[6] T. Dornheim et al, arXiv:2305.15305 (submitted)
[7] M. Böhme et al, Physical Review Letters 129, 066402 (2022)
[8] T. Dornheim et al, Journal of Chemical Physics 159, 164113 (2023)