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[en] Full text: In this contribution we will discuss a single spectral line in W₂₇₊ - an M1 line between the two ground state fine structure levels 4d₁₀4f ₂F_7/2 and ₂F_5/2. This is the only transition within the ground configuration of this ion and therefore a challenge to identify spectroscopically. We have studied this line both experimentally using an EBIT and theoretically using the GRASP2K code. These investigations were done independently and the results only compared when both methods had reached a conclusive wavelength, from careful and systematic considerations. One of the motivation for this work was the fact that earlier predictions for this transition showed a spread of over 400 Å for the wavelength. Our experiments were performed using the Shanghai permanent magnet EBIT and an Andor 303 Shamrock spectrometer equipped with an Andor Newton CCD camera. Tungsten was injected into the EBIT using the vaporous compound W(CO)₆. Spectra were recorded at several electron beam energies to isolate the W₂₇₊ line. The spectra were wavelength calibrated using a number of calibration lamps and the final experimental wavelength was determined to be 3377.43 ± 0.26 Å. To confirm the line was really from W₂₇₊ we determined the lifetime of the upper level of the ₂F term and compared our value with one from a calculation. As the line is from an M1 transition the lifetime of the upper level it is trivial to calculate the rate and thereby the lifetime. Our theoretical studies are systematic in two senses – first we investigate the contributions to the wavelength from different core subshells. These studies implies it is important to include core valence correlation even between the valence 4f and deep subshells – as a matter of fact, the correlation contribution from 3d is more pronounced than from 4d. The second dimension of the systematic approach is an increase of the active set of orbitals, and thereby the space of configuration state functions (CSFs) to show convergence of the final results. Finally, after these independent investigation we are able to do single-line spectroscopy to identify this transition, since the agreement between our experimental and theoretical wavelength is within the order 0.1%, since the experimental vacuum wavelength is 3378.43 Å whereas the calculated wavelength is 3374.73 Å. This is probably the best agreement for such a transition in the visible region for a highly charged high Z ion. We will also discuss cases in which this agreement could be even better, allowing for rigorous tests of minute effects – in the realm of Breit and QED interactions. (author)

[en] Theoretical investigations of the hyperfine quenching of the two metastable levels 1s²2s²2p⁶3s3p ³P₀ and ³P₂ 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 3s²¹S₀-3s3p ³P₂ and 3s3p ³P₁-3s3p ³P₂ 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 3s²¹S₀-3s3p ³P₀ transition are compared to earlier results and some disagreements are found and explained. The present predicted lifetime of 3s3p ³P₀ in ²⁷Al⁺ is slightly longer than the recent measurement, but in better agreement than earlier predictions.

[en] The multiconfiguration Dirac-Fock (MCDF) method was used to calculate the excitation energies of the levels of ³P and ¹P in the lowest excited configurations for the two homolog elements of No I and Yb I. Also the transition probability of the 7s7p ¹P₁→7s²¹S₀ transition and the ground-state ionization energy of No I were calculated. The results for Yb I agree very well with the available experiments, with deviations of below 0.6% for the triplets and below 4% for the singlet. The result for the No I excitation energies clears the situation of conflicting results between Borschevsky et al., 30 056 cm^-1 (3.726 eV) [Phys. Rev. A 75, 042514 (2007)], and Fritzsche, 3.36 eV [Eur. Phys. J. D 33, 15 (2005)] for the 7s7p ¹P₁ level, which is planned to be measured in the near future with a newly developed experimental technique by Backe et al. [Eur. Phys. J. D 45, 99 (2007)]. The ionization energy result obtained in this work, 53 701 cm^-1, is in excellent agreement with the scaled result of 53 600(600) cm^-1

[en] This paper contains a brief introduction to the main parameters of a micro-calorimeter designed to operate at the Shanghai electron beam ion trap. This is followed by short descriptions of some aspects of the calorimeter.

[en] This paper includes a discussion and classification of what is generally referred to as 'Forbidden lines' in atomic physics. Historical and important examples are reviewed, in light of their challenge to computations and remaining disagreements between experiment and theory. We also review some recent results on what could be labeled the third generation of unexpected transitions, induced by hyperfine quenching.

[en] Electron beam ion traps (EBITs) are very useful tools for disentanglement studies of atomic processes in plasmas. In order to assist studies on edge plasma spectroscopic diagnostics, a very low energy EBIT, SH-PermEBIT, has been set up at the Shanghai EBIT lab. In this work, simulation studies for factors which hinder an EBIT to operate at very low electron energies were made based on the Tricomp (Field Precision) codes. Longitudinal, transversal, and total kinetic energy distributions were analyzed for all the electron trajectories. Influences from the electron current and electron energy on the energy depression caused by the space charge are discussed. The simulation results show that although the energy depression is most serious along the center of the electron beam, the electrons in the outer part of the beam are more likely to be lost when an EBIT is running at very low energy. Using the simulation results to guide us, we successfully managed to reach the minimum electron beam energy of 60 eV with a beam transmission above 57% for the SH-PermEBIT. Ar and W spectra were measured from the SH-PermEBIT at the apparent electron beam energies (read from the voltage difference between the electron gun cathode and the central drift tube) of 60 eV and 1200 eV, respectively. The spectra are shown in this paper.

[en] Based on the multi-configuration Dirac–Hartree–Fock method and using the GRASPVU package, a theoretical investigation was performed to study the lifetimes of hyperfine levels of the first excited level 3d⁹4s ³D₃ in Ni-like ions (Z = 72–79) for all stable isotopes with nuclear spin. Comparisons between hyperfine-induced electric quadrupole transition rates and the pure magnetic octupole transition rates show that the extra electric quadrupole transition channel caused by the nuclear magnetic dipole and electric quadrupole hyperfine interaction is important for most hyperfine levels in each individual ion. Lifetimes of most hyperfine levels are sensitive to this extra decay channel. Extreme cases are found in ¹⁸¹Ta, ¹⁸⁵Re and ¹⁸⁷Re, where lifetimes of some hyperfine levels are shortened by more than an order of magnitude. (paper)

[en] In this paper we give a short introduction to the use of atomic spectroscopy in plasma diagnostics. Both older works and exciting new branches of atomic physics, which have relevance to diagnostics, are discussed. In particular we focus on forbidden lines in Be-like ions, lines sensitive to magnetic fields and levels which have a lifetime dependence on the nuclear spin of the ion, i.e. f-dependent lifetimes. Finally we mention a few examples of where tokamaks, instead of needing atomic data, actually provide new data and lead to developments in atomic structure studies.

[en] Dielectronic recombination (DR) process plays an important role in high temperature plasmas, where DR can affect charge balance and level populations significantly, and can cause radiative energy loss. Resolvable DR sourced satellite lines are often used for plasma temperature diagnostics, while the un-resolvable ones disturb determining spectral line shape, line intensity, and line position. Data of DR resonant strength is vital for accurate modeling of high temperature plasmas. DR studies are also important for testing atomic structure and atomic collision theories, since they carry information on quantum electrodynamics, relativistic effects, electron correlations and so on. Electron beam ion trap (EBIT) is an accelerator type device, which is capable of acting as both ion sources and light sources. EBIT can produce a special sort of plasma, in which electron energy is tunable and has a very narrow distribution. This made it possible for disentanglement studies on electron ion collision processes in plasmas. In this paper, experimental studies of DR processes based on electron beam ion traps (EBIT) will be discussed.