Non-thermal evolution of dense plasmas driven by intense x-ray fields

The advent of x-ray free-electron lasers has enabled a range of new experimental investigations into the properties of matter driven to extreme conditions via intense x-ray-matter interactions. The femtosecond timescales of these interactions lead to the creation of transient high-energy-density plasmas, where both the electrons and the ions may be far from local thermodynamic equilibrium. Predictive modelling of such systems remains challenging because of the different timescales at which electrons and ions thermalize, and because of the vast number of atomic configurations required to describe highly-ionized plasmas. Here we present CCFLY, a code designed to model the time-dependent evolution of both electron distributions and ion states interacting with intense x-ray fields on ultra-short timescales, far from local thermodynamic equilibrium. We explore how the plasma relaxes to local thermodynamic equilibrium on femtosecond timescales in terms of the charge state distribution, electron density, and temperature. X-ray free-electron lasers enable a range of new experimental investigations into the properties of matter driven to extreme conditions via intense x-ray-matter interaction. The proposed numerical method enables a quantitative investigation of transient high-energy-density plasmas driven by XFELs in femtosecond timescales even when both electrons and ions are far from local thermodynamic equilibrium.