Statistical and quantum photoionization cross sections in plasmas:Analytical approaches for any configurations including inner shells

Statistical models combined with the local plasma frequency approach applied to the atomic electron density are employed to study the photoionization cross-section for complex atoms.It is demonstrated that the Thomas–Fermi atom provides surprisingly good overall agreement even for complex outer-shell configurations,where quantum mechanical approaches that include electron correlations are exceedingly difficult.Quantum mechanical photoionization calculations are studied with respect to energy and nl quantum number for hydrogen-like and non-hydrogen-like atoms and ions.Ageneralized scaled photoionizationmodel(GSPM)based on the simultaneous introduction of effective charges for non-H-like energies and scaling charges for the reduced energy scale allows the development of analytical formulas for all states nl.Explicit expressions for nl1s,2s,2p,3s,3p,3d,4s,4p,4d,4f,and 5s are obtained.Application to H-like and non-H-like atoms and ions and to neutral atoms demonstrates the universality of the scaled analytical approach including inner-shell photoionization.Likewise,GSPMdescribes the near-threshold behavior and high-energy asymptotes well.Finally,we discuss the various models and the correspondence principle along with experimental data and with respect to a good compromise between generality and precision.The results are also relevant to large-scale integrated light–matter interaction simulations,e.g.,X-ray free-electron laser interactions with matter or photoionization driven by a broadband radiation field such as Planckian radiation.

Dielectronic recombination in non-LTE plasmas

Novel phenomena andmethods related to dielectronic capture and dielectronic recombination are studied for non-local thermodynamic equilibrium(LTE)plasmas and for applications to non-LTE ionization balance.It is demonstrated thatmultichannel autoionization and radiative decay strongly suppress higher-order contributions to the total dielectronic recombination rates,which are overestimated by standard approaches by orders of magnitude.Excited-state coupling of dielectronic capture is shown to be much more important than ground-state contributions,and electron collisional excitation is also identified as a mechanism driving effective dielectronic recombination.A theoretical description of the effect of angularmomentum-changing collisions on dielectronic recombination is developed from an atomic kinetic point of view and is visualized with a simple analytical model.The perturbation of the autoionizing states due to electric fields is discussed with respect to ionization potential depression and perturbation of symmetry properties of autoionizationmatrix elements.The first steps in the development of statistical methods are presented and are realized in the framework of a local plasma frequency approach.Finally,the impact of collisional–radiative processes and atomic population kinetics on dielectronic recombination is critically discussed,and simple analytical formulas are presented.