Theoretical Research On The Electric Dipole Radiative Transitions In Highly Charged Ions

Highly charged ions exist widely in hot plasma environment,which are the fundamental constitution of partially ionized plasma.The studies of radiative processes of these ions are very important for the relevant scientific research fields involving high-temperature plasmas,such as the X-ray astronomy and controllable nuclear fusion.Because most electrons are ionized in these systems with high nuclear charge,strong Coulomb interactions between the nuclear charge and electrons are dominant,which makes the highly charged ion systems have different features comparing with normal atomic systems.The relativistic and quantum electrodynamics effects become relatively prominent.On the other hand,due to the strong Coulomb attraction from the nuclei,the electrons move in a smaller space and time scale.As a result,the short lived inner-shell-electron excited resonance states also become important in the related dynamical processes.In this thesis,based on the physical features of highly charged ions,we investigate their electric dipole radiative transitions,which can be divided into the following three parts:Firstly,we study the strong electric dipole radiative transitions between 2p and 1s orbitals in the Li-like 1s¹2p²and B-like 1s¹2s²2p²doubly excited resonance states.We find the relativistic effect of electron correlations（i.e.,the Breit interaction）can have a substantial influence on the many-body wavefunctions of these states with strong intra-shell electron correlations,and thus change the related radiative transitions drastically.Furthermore,based on theoretical simulations,we find that these states can be populated efficiently through dielectronic recombination processes,and propose an experiment to observe this effect,which has been confirmed by a recent experiment.This work extends the conventional wisdom on the role of the relativistic effects in the electric dipole radiative transitions of highly charged ions,which could be useful for future precise high-temperature plasma diagnostics.Secondly,we address a recent precise experiment performed in the X-ray free electron laser facility for measuring the oscillator strength ratio between the 3C and 3D lines of Fe¹⁶⁺ions,which is related with a famous astrophysical problem.We study the linear cascade atomic processes in the interaction between the Fe¹⁵⁺/Fe¹⁶⁺ions and the X-ray free electron laser systematically,and find out that the inconsistency between the experimental measurement and theoretical value is due to the population transfer from Fe¹⁵⁺ions to Fe¹⁶⁺ions induced by the intense incident light.We conclude that the present experimental result is not able to elucidate the possible unreliability in the theoretical value,which indicates that other factors need to be taken into account to ultimately resolve the astrophysical observation problem related with this 3C/3D line ratio.Finally,considering highly charged ions widely exist in hot plasma environment,it is worth investigating the influence of the plasma environment to the radiative transitions.By using the modified Debye-Hückel approximation where the time and space scales of the radiative transitions are taken into account,we study the transition energies and oscillator strengths of the 3C and 3D emission lines of Ne-like ions under different plasma shielding environment.We find the spin-orbit coupling effect can be relatively enhanced by the plasma screening,which has a significant effect on the transition rate.We also propose a fitting scheme for these atomic parameters in the whole isoelectronic sequence of Ne-like ions,which could be used in related simulation studies conveniently.