Kinetic Modeling of Ultraintense X-Ray Laser-Matter Interactions*

High-intensity XFELs have become a novel way of creating and studying hot dense plasmas. The LCLS at Stanford can deliver a millijoule of energy with more than 10$^{12}$ photons in a $\sim$ 100 femtosecond pulse [1]. By tightly focusing the beam to a micron-scale spot size, the XFEL can be intensified to more than 10$^{18}$ W/cm$^{2}$, making it possible to heat solid matter isochorically beyond a million degrees (\textgreater 100 eV). Such extreme states of matter are of considerable interest due to their relevance to astrophysical plasmas. Additionally, they will allow novel ways of studying equation-of-state and opacity physics under Gbar pressure and strong fields. Photoionization is the dominant x-ray absorption mechanism and triggers the heating processes. A photoionization model that takes into account the subshell cross-sections has been developed in a kinetic plasma simulation code, PICLS, that solves the x-ray transport self-consistently [2]. The XFEL--matter interaction with several elements, including solid carbon, aluminum, and iron, is studied with the code, and the results are compared with recent LCLS experiments. \\[4pt] [1] S. M. Vinko \textit{et al.}, \textit{Nature} \textbf{482}, 59-62 (2012).\\[0pt] [2] Y. Sentoku \textit{et al.}, \textit{Phys. Rev. E} \textbf{90}, 051102 (2014).