Relativistic R-matrix Study On The Photoionization Process Of Highly Charged Tungsten Ions

The photoionization process is one of the most basic processes,in which light interacts with atoms or ions.The study of photoionization process is of great significance for atomic physics,plasma physics,and astrophysics.The electron correlation effect,finite-nuclear size effect,quantum-electrondynamical effect,and relativistic effect can be investigated by analysing detailedly the photoionization of highly charged ions.Therefore,the photoionization cross section of atoms or ions is an important parameter for simulating the opacity of laboratory and astrophysical plasmas.The central temperature of fusion plasmas in the International Thermonuclear Experimental Reactor(ITER)under construction will exceed 30ke V,which would make the wall material tungsten become more or less tungsten ion impurity into the plasmas.Since the impurity mainly consists of W⁶³⁺and W⁶⁴⁺ions,atomic properties of the impurity ions can be used to diagnose fusion plasmas,for which one needs understand various atomic processes of tungsten ions,such as,dielectronic recombination,photorecombination,electron-impact ionization,electron-impact excitation,and photoionization.For this reason,the studies of these processes are of great significance for accurately simulating and diagnosing the ITER plasmas.In this work,the photoionization of highly charged W⁵⁹⁺-W⁶¹⁺and W⁶³⁺ions is systematically studied by using the DARC package based on the Dirac R-matrix method.The main content is as follows:1.The photoionization of the ground state(1s²2s²2p⁶3s ²S_1/2)and four lowlyexcited states(1s²2s²2p⁶3p ²P_1/2,_3/2and 1s²2s²2p⁶3d ²D_3/2,_5/2)of sodiumlike W⁶³⁺ions is studied by using the DARC and GRASP2K packages based on the fully relativistic R-matrix theory and the multiconfigurational Dirac-Fock method,respectively.The direct ionization limit and the convergence limit of the Rydberg series are ideatified in detail,and the resonance energies are given.In order to analyze the resonant photoionization cross sections,the Flexible Atomic Code package is used to calculate the energy levels of W⁶³⁺ions,and the energy levels and resonance energies of sparse resonance structure are obtained.2.The photoionization of the ground states of aluminum-like W⁶¹⁺ions,silicon-like W⁶⁰⁺ions,and phosphorus-like W⁵⁹⁺ions are also systematically studied by using the DARC and GRASP2K packages based on the fully relativistic R-matrix theory and the multiconfigurational Dirac-Fock method,respectively.The corresponding energy levels and resonance energies are gained by analysing the direct ionization limit and the convergence limit of the Rydberg series.Resonance peaks after the direct ionization are analyzed by using the FAC package.Moreover,the ground state photoionization cross sections of W⁶³⁺-W⁵⁹⁺ions are compared with each other,and the change of photoionization cross sections with the number of valence electrons is analyzed.