Non-equilibrium transition from X-ray-heated to collision-driven plasma

Sang-Kil Son

[BibTeX]https://vuvx2026.se

A transient plasma is formed when intense X-ray pulses interact with matter. Multiphoton ionization produces highly charged ions and hot electrons, and eventually reach a thermal equilibrium. I will present a joint theoretical and experimental study of X-ray multiphoton ionization dynamics and plasma evolution dynamics of near-ambient pressure neon gas interacting with intense X-ray pulses generated by European XFEL. The target density is low enough to model excitation mechanisms in the isolated- atom limit during the pulse, while it is high enough to observe collisional effects afterwards. Multiple resonance excitations are investigated in X-ray emission spectra from all Ne charge states as shown in the figure (theoretical 2D map of X-ray emission spectra). I will also discuss how insights from atomic physics are applied to understand photon-driven plasma formation. Time-resolved X-ray emission measurement enables us to monitor non-equilibrium transition dynamics from a photoionized plasma to collision-dominated regime within nanoseconds, providing insight into thermalization and expansion dynamics of the hundred-eV hot plasma. Our study of quantum-state-resolved X-ray multiphoton ionization dynamics opens up new opportunities for high-resolution X-ray spectroscopy of atoms and plasmas at high intensity.

Tags: MRIXS, XFEL, plasma, explosion, XATOM, EuXFEL, CFEL, DESY