Yaming Zou

MCDF calculations for the lowest excited states in the Zn-like sequence

We report on large scale ab initio calculation for the 4s(2) S-1(0)-4s4p P-1,3(0,1,2) transitions in the zinc-like sequence, using the multiconfiguration Dirac Fock ( MCDF) method. Our attention is focused on the spin-forbidden transition 4s(2) S-1(0)-4s4p P-3(1) and the hyperfine- induced ( HPF) transition 4s(2) S-1(0)-4s4p P-3(0) for ions between Z = 30 ( Zn) and Z = 47 ( Ag). Our results provide a base for settling the existing conflicts in previous experimental and theoretical data for these transitions. We also report on rates of forbidden lines within the 4s4p P-3 term and between this term and the ground state. Accurate values for the hyperfine constants, showing excellent agreement with experimental values where available, are also given. We also give transition energies and lifetimes for the 4s2 S-1(0)-4s4p P-1(1) resonance line.

Correlative multielectron processes in K-shell photoionization of Ca, Ti and V in the energy range of 8-35 keV

The Kalpha satellite spectra arising from the correlative multielectron processes accompanying K-shell photoionization of Ca, Ti and V were measured using a broad range crystal spectrometer. Multiconfiguration Dirac-Fock calculations were performed to interpret the observed,x-ray energies and the spectral line shape., The calculations agree fairly well with the experimental results. The variation of the KalphaL(1) satellite and the Kalpha(1,2)(h) hypersatellite intensities was measured as a function, of excitation energy in the range of 8-35 keV. The KalphaL(1)/Kalpha(1,2) intensity ratio for each,element is already saturated in our energy range, and the asymptotic values of 1.58 +/- 0.08, 1.26 +/- 0.06 and 0.97 +/- 0.05% for Ca, Ti. and V were determined. By combining the present results and the previously measured values for various elements, we have found a Z(-3.5) scaling law for the KalphaL(1)/Kalpha(1,2) intensity ratio, The measured Kalpha(1,2)(h)/Kalpha(1,2) for each element, is found to increase smoothly from its onset and shows a long saturation range extending up to at least 25 keV above the threshold for Ti. The evolution of the Kalpha(1,2)(h)/Kalpha(1,2) intensity ratio is compared with the analytic Thomas model and with the theoretical calculation based on the screened hydrogenic model. (Less)

EBIT spectroscopy of Pm-like tungsten

Methods of VUV electron beam ion trap (EBIT) spectroscopy are applied to the study of Pm-like tungsten (W13+). These data show that theory appears well capable of dealing with these multi-electron (61) ions, at least for high ionization stages. A comparison of other spectroscopic methods applied to the study of other ions of the Pm I sequence is also given, and finally a search for the Pm-like W lines at the ASDEX Upgrade Tokamak is mentioned

EXTENDED CALCULATIONS WITH SPECTROSCOPIC ACCURACY: ENERGY LEVELS AND TRANSITION PROPERTIES FOR THE FLUORINE-LIKE ISOELECTRONIC SEQUENCE WITH Z = 24–30

We have performed extensive multiconfiguration Dirac-Hartree-Fock calculations and second-order many-body perturbation calculations for F-like ions with Z = 24-30. Energy levels and transition rates for electric dipole (E1), electric-quadrupole (E2), electric-octupole (E3), magnetic dipole (M1), and magnetic-quadrupole (M2) transitions, as well as radiative lifetimes, are provided for the lowest 200 levels belonging to the 1s22s22p5, 1s22s22p6, 1s22s22p43l, 1s22s2p23l, 1s22p63l, and 1s22s22p44l configurations of each ion. The results from the two sets of calculations are in excellent agreement. Extensive comparisons are also made with other theoretical results and observed data from the CHIANTI and NIST databases. The present energies and wavelengths are believed to be accurate enough to aid line identifications involving the n = 3 and n = 4 configurations, for which observations are largely missing. The calculated wavelengths and transition data will be useful in the modeling and diagnostics of astrophysical and fusion plasmas. (Less)

Precise studies on resonant energies of the first intershell (KLL) dielectronic recombination processes for He- up to O-like xenon

Precise studies of the resonant energies of KLL dielectronic recombination (DR) processes of He-, Li-, Be-, B-, C-, N-, and O-like xenon ions were performed at the Shanghai Electron Beam Ion Trap [X. Zhu et al., Nucl. Instrum. Methods Phys. Res. B 235, 509 (2005)], employing home developed high precision, high stability high voltage dividers. Influences from retardation by the capacitor of experimental setup, contact potential, space charge of the electron beam, and of ion neutralization, as well as fringing field effects were taken into account. The obtained resonant energies were, at an average uncertainty level of 0.03%, compared with calculation results by relativistic configuration interaction (RCI) theory, relativistic many-body perturbation theory (RMBPT), and by multiconfiguration Dirac–Fock (MCDF) theory. All the three predicted DR resonant energies by MCDF agree with our experiments. Among the 15 predictions by RMBPT, 13 are in good agreement with our experimental results. But only five out of 1...

Hyperfine dependent lifetimes in Mg-like ions

Theoretical investigations of the hyperfine quenching of the two metastable levels 1s(2)2s(2)2p(6)3s3p P-3(0) and P-3(2) have been performed along the magnesium-like iso-electronic sequence ranging from Z = 12 to Z = 31. It is shown that the lifetime of the latter level is sensitive to hyperfine quenching in the beginning of the sequence, but that this sensitivity decreases going to higher Z. It is also shown that the branching fractions of the 3s(2) S-1(0)-3s3p P-3(2) and 3s3p P-3(1)-3s3p P-3(2) transitions are very sensitive to hyperfine quenching, which could lead to some dramatic effects in the spectrum. Our predicted transition rates of the hyperfine induced 3s(2) S-1(0)-3s3p P-3(0) transition are compared to earlier results and some disagreements are found and explained. The present predicted lifetime of 3s3p P-3(0) in Al-27(+) is slightly longer than the recent measurement, but in better agreement than earlier predictions. (Less)

Energy levels and transition rates for helium-like ions with Z = 10–36

Aims. Helium-like ions provide an important X-ray spectral diagnostics in astrophysical and high-temperature fusion plasmas. An interpretation of the observed spectra provides information on temperature, density, and chemical compositions of the plasma. Such an analysis requires information for a wide range of atomic parameters, including energy levels and transition rates. Our aim is to provide a set of accurate energy levels and transition rates for helium-like ions with Z = 10–36. Methods. The second-order many-body perturbation theory (MBPT) was adopted in this paper. To support our MBPT results, we performed an independent calculation using the multiconfiguration Dirac-Hartree-Fock (MCDHF) method. Results. We provide accurate energies for the lowest singly excited 70 levels among 1 snl ( n ≤ 6 ,l ≤ ( n −1)) configurations and the lowest doubly excited 250 levels arising from the K-vacancy 2 l n ′ l ′( n ′ ≤ 6, l ′ ≤ ( n ′−1)) configurations of helium-like ions with Z = 10−36. Wavelengths, transition rates, oscillator strengths, and line strengths are calculated for the E1, M1, E2, and M2 transitions among these levels. The radiative lifetimes are reported for all the calculated levels. Conclusions. Our MBPT results for singly excited n ≤ 2 levels show excellent agreement with other elaborate calculations, while those for singly excited n ≥ 3 and doubly excited levels show significant improvements over previous theoretical results. Our results will be very helpful for astrophysical line identification and plasma diagnostics.

Energy levels and radiative data for Kr-like W38+ from MCDHF and RMBPT calculations

Energies, transition rates, line strengths and lifetimes have been computed for all levels of the 4p 6 and 4p 54d configurations of W38+ by using the multi-configuration Dirac-Hartree-Fock (MCDHF) method as well as relativistic many-body perturbation theory. We investigate systematically correlation, relativistic and quantum electro-dynamical (QED) effects of different properties, including excitation energies and transition rates. We demonstrate that it is important to include the core-valence correlation of rather deep subshells (including 3d and 3p) to reach close to spectroscopic accuracy for the transition energies. We also show that high-multipole transitions (E3, M2) are important for the lifetime of some metastable levels of 4p 54d (). The present results are in good agreement with experiments and of considerably higher accuracy than those achieved in previous theoretical works.

Review of highly charged tungsten spectroscopy research using low energy EBITs at the Shanghai EBIT laboratory

We present an overview of recent work on the spectroscopy of tungsten ions, related to tokamak edge plasma. The spectra were recorded from the newly-built low energy electron beam ion traps (EBITs) in the Shanghai EBIT laboratory. By analyzing the spectra with the help of accurate theoretical calculations, using state-of-the-art techniques, we were able to identify term and fine structure splittings in the ground and the first excited configuration for a number of charge states. The theoretical models included a careful study of correlation and showed an excellent agreement with our experimental results for transition energies and rates. Some metastable levels which have extremely long lifetime and high population were found, and the influences of these levels on the charge state distribution of tungsten ions in tokamaks are discussed.

A portable high-resolution soft x-ray and extreme ultraviolet spectrometer designed for the Shanghai EBIT and the Shanghai low energy EBITs

A portable high resolution soft x-ray and extreme ultraviolet (EUV) spectrometer has been developed for spectroscopic research at the Shanghai Electron Beam Ion Trap (EBIT) laboratory. A unique way of aligning the grazing incidence spectrometer using the zero order of the grating is introduced. This method is realized by extending the range of the movement of the CCD detector to cover the zero order. The alignment can be done in a few minutes, thus leading to a portable spectrometer. The high vacuum needed to be compatible with the EBITs is reached by mounting most of the translation and rotation stages outside the chamber. Only one high vacuum compatible linear guide is mounted inside the chamber. This is to ensure the convenient interchange of the gratings needed to enable wavelength coverage of the whole range of 10 to 500 Å. Spectra recorded with one of our low energy EBITs shows that a resolving power of above 800 can be achieved. In the slitless configuration used in this work, we found the resolving power to be limited by the width of the EBIT plasma. When mounted on the Shanghai EBIT which is a high energy EBIT and has a narrower EBIT plasma width, the estimated resolving power will be around 1400 at 221.15 Å.