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Center for Nonlinear Studies |
New and exotic states of matter of highly transient and non-equilibrium plasmas have been created in laboratories with the development of X-ray free electron lasers (XFEL). XFEL lasers are operating in USA (LCLS), Japan (SACLRA), Korea (PAL-XFEL) and Germany (European XFEL) with as high as 1012 photons in the energy range of 0.8 to 20 keV. Interactions of x-ray photons with atoms, molecules, solids and biomolecules have been studied with spectroscopic measurements and measured photons reveal complex atomic processes in these plasmas and show a glimpse of electronic structures of finite-temperature non-equilibrium dense plasmas. XFEL produced plasmas also demonstrate non-linear absorption characteristics such as saturable absorption or reverse saturable absorption. As high intensity X-ray laser beams interact with a solid density target, electrons are ionized from inner-shell orbitals and these electrons and XFEL photons create dense and finite temperature plasmas. In order to study atomic processes in XFEL driven plasmas, the atomic kinetics model SCFLY containing an extensive set of configurations needed for solid density plasmas is applied to study atomic processes of XFEL driven systems. With time-dependent conditions of the XFEL given as input parameters, the code computes time-dependent population distributions and ionization distributions self-consistently with electron temperatures and densities assuming an instantaneous equilibration of electron energies. In this presentation, unique aspects of atomic processes in XFEL driven plasmas are described with comparisons between the model and the measurements.
Host: Xianzhu Tang