Towards atomic physics in particle in cell on GPUs (PIConGPU), photon scattering and nanometer and femtosecond probing of hot dense matter with SAXS

Ultrafast heating of solids or solid density plasmas can provide a unique, transient and non-thermal state of matter that enables the study e.g. of ultrafast ionization and excitation, recombination, photon and electron transport. Heating can be achieved directly and indirectly by irradiation with ultra-intense optical lasers or volumetrically with XFELs. Yet, the state-of-the-art theoretical description needed to simulate those processes in particle in cell (PIC) simulations is based on average and effective simplistic assumptions, and hence not reliable for ultrashort, non-thermal states. We present our approach and status of implementing explicit atomic physics in PIConGPU, and introduce the first spin-off tool ParaTAXIS that simulates explicitly photon scattering using PIC methods. This enables implementation of arbitrary scattering physics, multiple scattering, full treatment of X-ray beam properties and fast plasma dynamics. We also demonstrate a novel experimental method based on Small Angle X-ray Scattering to probe such physics on a few nanometer and few femtosecond level simultaneously in ultra-intensity optical laser heated solids.