Lu-You Xie

Relativistic effects in the photoionization of hydrogen-like ions with screened Coulomb interaction

The relativistic effects in the photoionization of hydrogen-like ion with screened Coulomb interaction of Yukawa type are studied for a broad range of screening lengths and photoelectron energies. The bound and continuum wave functions have been determined by solving the Dirac equation. The study is focused on the relativistic effects manifested in the characteristic features of photoionization cross section for electric dipole nl→e,l±1 transitions: shape resonances, Cooper minima and cross section enhancements due to near-zero-energy states. It is shown that the main source of relativistic effects in these cross section features is the fine-structure splitting of bound state energy levels. The relativistic effects are studied in the photoionization of Fe25+ ion, as an example.

Energy levels and transition probabilities for possible X-ray laser lines of highly charged Ni-like ions

Abstract The 45 low-lying energy levels and the transition probabilities among these levels connected with possible X-ray laser lines are calculated for Ni-like ions from Z=74 to 84. In the calculations, main correlation, relaxation and relativistic effects are considered. The calculated energy levels and transition probabilities are compared with some experimental and theoretical results. Finally, the contributions of lots of weak correlations on the transition wavelengths and probabilities are discussed by including partly single and double excitations from the 3l inner-shells into the 4l and 5l orbital layers.

Electron Impact Excitation and Dielectronic Recombination of Highly Charged Tungsten Ions

Electron impact excitation (EIE) and dielectronic recombination (DR) of tungsten ions are basic atomic processes in nuclear fusion plasmas of the International Thermonuclear Experimental Reactor (ITER) tokamak. Detailed investigation of such processes is essential for modeling and diagnosing future fusion experiments performed on the ITER. In the present work, we studied total and partial electron-impact excitation (EIE) and DR cross-sections of highly charged tungsten ions by using the multiconfiguration Dirac–Fock method. The degrees of linear polarization of the subsequent X-ray emissions from unequally-populated magnetic sub-levels of these ions were estimated. It is found that the degrees of linear polarization of the same transition lines, but populated respectively by the EIE and DR processes, are very different, which makes diagnosis of the formation mechanism of X-ray emissions possible. In addition, with the help of the flexible atomic code on the basis of the relativistic configuration interaction method, DR rate coefficients of highly charged W to W ions are also studied, because of the importance in the ionization equilibrium of tungsten plasmas under running conditions of the ITER.

Theoretical study of the photoionization process of Ne-like Ar, Fe, Kr and Xe ions

Photoionization (PI) cross sections of the ground state 1s2 2s2 2p6 1 S0 of Ne-like Ar8+, Fe16+, Kr26+ and Xe44+ ions are calculated by using the Dirac atomic R-matrix code based on a fully relativistic R-matrix method. To analyze the detailed resonant structure, systematical calculations based on the multiconfiguration Dirac–Fock method are performed for the dominant 2s → np resonant transitions, and the resonant energies, strengths and total natural widths are presented. The resonant structures and characteristics of the PI cross sections and resonance strengths along the Ne-like sequence are discussed with emphasis on the influence of relativistic effects. For the Ar8+ ion, good agreement is found between the present results and available theoretical calculations and experimental data.

Influence of Debye plasma on the cross section and linear polarization of x-ray radiation following inner-shell electron-impact excitation of highly charged Be-like Sc17+ ions

Detailed calculations using a fully relativistic distorted-wave method incorporating the Debye–Huckel potential are carried out for the electron-impact excitation cross sections from the ground state 1s22s2 (J = 0) to the individual magnetic sublevels of 1s2s22p and states of highly charged Be-like ions in the presence of a plasma environment. The effects of plasma screening on the cross section and linear polarization of the corresponding x-ray emission are investigated. For the line, it is found that the plasma screening has a pronounced effect and causes the cross section to decrease over the whole energy range considered. This dramatic influence also leads to a remarkable decrease in the linear polarization of subsequent x-ray radiation. However, for the line, the plasma screening effect on the cross sections is relatively larger than for the excitations, while its influence on the linear polarization of the radiation is very small.

Electron impact excitation of xenon from the metastable state to the excited states

The electron impact excitation cross sections from the lowest metastable state 5p56sJ = 2 to the six lowest excited states of the 5p56p configuration of xenon are calculated systematically by using the fully relativistic distorted wave method. In order to discuss the effects of target state descriptions on the electron impact excitation cross sections, two correlation models are used to describe the target states based on the multiconfiguration Dirac–Fock (MCDF) method. It is found that the correlation effects play a very important role in low energy impact. For high energy impact, however, the cross sections are not sensitive to the description of the target states, but many more partial waves must be included.

The theoretical studies on the electron-impact single ionization of Se3+

We have performed fully relatively level-to-level distorted-wave (LLDW) calculations for both direct ionization (DI) and excitation autoionization (EA) of ground state Se3+ ion using the flexible atomic code (FAC). Large EA contributions come from the excitations 4p to nl and 3d to nl. Our calculated total DI+EA cross section have been compared with the recent experimental results. It suggests that the contributions of resonace-excitation double-autoionization process (REDA) to electron impact single ionization of Se3+ at the near threshold are more than 25%.

Photoionization of C5+ ion in warm dense plasmas

The photoionization process of the C5+ ion in warm, dense plasmas is studied using the relativistic approximation. Cross section calculations are performed for plasma density and temperature ranges of ne ∼ 1023–1026 cm−3 and Te = 150–300 eV, respectively. The used static screened potential includes the effects of plasma degeneracy, finite-temperature gradient corrections to the kinetic energy, and quantum exchange-correlation. The dependencies of the photoionization cross section on plasma density (for fixed temperature) and temperature (for fixed density) are investigated.The photoionization process of the C5+ ion in warm, dense plasmas is studied using the relativistic approximation. Cross section calculations are performed for plasma density and temperature ranges of ne ∼ 1023–1026 cm−3 and Te = 150–300 eV, respectively. The used static screened potential includes the effects of plasma degeneracy, finite-temperature gradient corrections to the kinetic energy, and quantum exchange-correlation. The dependencies of the photoionization cross section on plasma density (for fixed temperature) and temperature (for fixed density) are investigated.

Relativistic R-matrix calculations for L-shell photoionization cross sections of C II

Sabri Bouchoucha, Kamel Alioua, Moncef Bouledroua Chin. Phys. B . 2017, 26(7): 073202. doi: 10.1088/1674-1056/26/7/073202 Low-lying electronic states of CuN calculated by MRCI method Shu-Dong Zhang(张树东), Chao Liu(刘超) Chin. Phys. B . 2016, 25(10): 103103. doi: 10.1088/1674-1056/25/10/103103 Influence of the interaction volume on the kinetic energy resolution of a velocity map imaging spectrometer Peng Zhang(张鹏), Zheng-Peng Feng(冯正鹏), Si-Qiang Luo(罗四强), Zhe Wang(王哲) Chin. Phys. B . 2016, 25(3): 033202. doi: 10.1088/1674-1056/25/3/033202 An ab initio investigation of the low-lying electronic states of BeH

Long-range dispersion interactions between excited states of K and rare-gas atoms

The long-range interaction potential plays an important role in the current research in the field of cold atoms[1-3]. such as Bose-Einstein condensation, ultra-cold collisions, and ultra-cold photo-association spectra. Precisely definition of the interaction potential between alkali metal and rare gas atoms has attracted much interest due to its signification in cold atom physics in recent years. For example, the stability and structure of BoseEinstein condensation (BEC)[1] depend on the sign (and magnitude ) of the scattering length, and the scattering length depends on the precise values of the dispersion constants. The long-range van der Waals dispersion coefficients between two atoms, is one of the more important parts of long-range potential. In this work, the long-range interaction between low-lying states of K and the ground state of rare gas atoms are calculated in JJ coupled states, in which the spin-orbital interactions are included. The energy levels and transition arrays that contribute to the dispersion parameters are computed by using the relativistic semiempirical-core-potential method (RCICP)[4]. The rare gas oscillator strengths distributions are derived by using calculations of rare-gas polarizabilities and dispersion coefficients to tune Hartree-Fock single-particle energies and expectation values [5]. The present dispersion coefficients between the ground state of Ar and low-lying states of K are listed in Table 1 and compared with others available values [5]. The dispersion coefficients between the ground state of K and the ground state of rare gas atoms have been calculated in our previous paper [6]. The present results are in good agreement with the configuration interaction plus core polarization (CICP) results [5].