Chenzhong Dong

M1 transition energies and probabilities between the multiplets of the ground state of Ag-like ions with Z = 47–92

Extensive relativistic configuration interaction calculations have been performed for the 4d104f and 4d105s states of the Ag-like isoelectronic ion using the GRASP2K package based on the multi-configuration Dirac–Fock method. The active space techniques have been employed to extend the configuration expansion systematically. The electron correlation effects, Breit interaction and quantum electrodynamics effects to the atomic state wavefunctions and the corresponding energies have been taken into account. Good agreement has been obtained in a general trend with the existing experimental and theoretical values. The change of the ground state configuration from 4d105s to 4d104f is predicted to occur at Z = 62. The transition energy and probability of the M1 transition between the 4d104f multiplets are, respectively, scaled to be 0.01(Z*)4 cm−1 and 1.95 × 10−17(Z*)11.97 s−1, where Z* = Z − 34.42 is the effective nuclear charge number for Ag-like ions with Z ⩾ 62. Our results show the need for more high-precision experiments for Z ⩾ 68 ions.

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.

Ab initio multi-configuration Dirac–Fock calculation of M1 visible transitions among the ground state multiplets of the W26 + ion

The development of fusion reactors has generated a demand for improved knowledge of the atomic properties of tungsten. Using a multi-configuration Dirac–Fock (MCDF) method with a restricted active space treatment, the wavelengths and transition probabilities of the M1 and E2 transitions in the visible light region are calculated for the ground state multiplets of W26 + ions. The theoretical wavelength (388.43 nm) for the 3H5 → 3H4 magnetic dipole transition agrees quite well with the experimental value (389.41 nm). Other transitions theoretically predicted at longer wavelengths are also in good agreement with new experimental observations. The results also indicate that the core–core correlation contributions from the 4d shell are essential to determine the transition properties accurately.

Two-electron?one-photon M1 and E2 transitions between the states of the 2p3 and 2s22p odd configurations for B-like ions with 18 ? Z ? 92

Two-electron–one-photon (TEOP) M1 and E2 transition energies, line strengths and transition probabilities between the states of the 2p3 and 2s22p odd configurations for B-like ions with 18 ≤ Z ≤ 92 have been calculated using the GRASP2K package based on the multiconfiguration Dirac–Hartree–Fock (MCDHF) method. Employing active-space techniques to expand the configuration list, we have systematically considered the valence, core–valence and core–core electron correlation effects. Breit interaction and quantum electrodynamical (QED) effects were also included to correct atomic state wavefunctions and the corresponding energies. Influences of electron correlation, Breit interaction and QED effects on transition energies and line strengths of the TEOP M1 and E2 transitions were analysed in detail. The present results were also compared with other theoretical and experimental values.

Hyperfine quenching of the 3s3p 3P0 level in Mg-like ions

Hyperfine quenching rates of the 3s3p3P0 level in Mg-like ions were calculated using the GRASP2K package based on the multi-configuration Dirac–Hartree–Fock method. Valence and core-valence correlation effects were accounted for in a systematic way. Breit interactions and QED effects were included in the subsequent relativistic CI calculations. Calculated rates were compared with other theoretical values and with experiment, and a good agreement with the latest experimental value for the ion (Rosenband et al 2007 Phys. Rev. Lett. 98 220801) was found. Furthermore, we showed in detail the contributions from Breit interaction and QED effects to concerned physical properties. Finally, electronic data were presented in terms of a general scaling law in Z that, given isotopic nuclear spin and magnetic moment, allows hyperfine-induced decay rates to be estimated for any isotope along the isoelectronic sequence.

Relativity, electron correlation and QED effects in the 1s2s2 2S1/2 state of highly charged Li-like ions

On the basis of a multiconfiguration Dirac?Fock method, a systematic study has been carried out for the decay process of the 1s2s2 2S1/2 state of Li-like ions. It is found that the decay properties of these states are quite different along the isoelectronic sequence: for low-Z ions up to Z = 30, the Auger decay channel is dominant; for medium-Z ions up to Z = 80, a two-electron one-photon radiative decay caused by a strong electron correlation becomes a competitive channel; and for very heavy ions about Z = 90, the magnetic dipole radiative decay becomes important too. In addition, the QED contributions to the excitation energy and the contributions from the Breit interaction to the Auger decay rates are stressed for heavy ions in particular.

Collisional-Radiative Model for the visible spectrum of

Abstract Plasma diagnostics in magnetic confinement fusion plasmas by using visible spectrum strongly depends on the knowledge of fundamental atomic properties. A detailed collisional-radiative model of W 26+ ions has been constructed by considering radiative and electron excitation processes, in which the necessary atomic data had been calculated by relativistic configuration interaction method with the implementation of Flexible Atomic Code. The visible spectrum observed at an electron beam ion trap (EBIT) in Shanghai in the range of 332 nm to 392 nm was reproduced by present calculations. Some transition pairs of which the intensity ratio is sensitive to the electron density were selected as potential candidates of plasma diagnostics. Their electron density dependence is theoretically evaluated for the cases of EBIT plasmas and magnetic confinement fusion plasmas.

W^{26+}

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.

ions

On the basis of previous work, the hyperfine-induced 3s3p P-3(2) -> 3s(2) S-1(0) E1 transition probabilities of Mg-like ions were further calculated using the GRASP2K package based on the multiconfiguration Dirac-Hartree-Fock method. The contribution to the lifetime of the P-3(2) level from the 3s3p P-3(2) -> 3s(2) S-1(0) hyperfine-induced E1, 3s3p P-3(2) -> 3s3p P-3(1) M1, 3s3p P-3(2) -> 3s(2) S-1(0) M2 and 3s3p P-3(2) -> 3s3p P-3(0,1) E2 transition was discussed in detail. It was found that hyperfine interaction has an obvious effect on the lifetime at the beginning of the Mg-like isoelectronic sequence.

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

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.