| 1. |
- Ali, Safdar, et al.
(author)
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Electron-ion recombination of H- and He-like sulfur
- 2011
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In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 44:22, s. 225203-
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Journal article (peer-reviewed)abstract
- Electron-ion recombination of sulfur ions with electrons in the energy range of 1.6-3 keV was studied at the Stockholm Refrigerated Electron Beam Ion Trap. We obtained the KLn dielectronic recombination (DR) cross sections up to n = 5 for H-like and He-like sulfur ions by observing the x-rays from the trapped ions. A fully relativistic distorted wave approximation method was used for calculating the DR cross sections, while the resonance energies were obtained with a multiconfiguration Dirac-Fock approach using the GRASP II code. The calculations agree with the experimental results within the experimental error bars. Additionally, the obtained total DR resonance strengths were used to check the behaviour of a scaling formula for low-Z, He-like iso-electronic sequence (Watanabe et al 2001 J. Phys. B: At. Mol. Opt. Phys. 34 5095).
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| 2. |
- Ali, Safdar, et al.
(author)
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Electron-ion recombination rate coefficients for C II forming C I
- 2012
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 753:2, s. 132-
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Journal article (peer-reviewed)abstract
- We have determined absolute dielectronic recombination rate coefficients for C II, using the CRYRING heavy-ions storage ring. The resonances due to 2s-2p (∆n = 0) core excitations are detected in the center-of-mass energy range of 0-15 eV. The experimental results are compared with intermediate coupling AUTOSTRUCTURE calculations. Plasma rate coefficients are obtained from the DR spectrum by convoluting it with a Maxwell-Boltzmann energy distribution for temperatures in the range of 103-106 K. The derived temperature dependent plasma recombination rate coefficients are presented graphically to compare with the theoretical data available in literature and parameterized by using a fit formula for convenient use in plasma modelling codes. In the temperature range of 103-2×104 K, our experimental results show that previous calculations severely underestimate the plasma rate coefficients and also our AUTOSTRUCTURE calculation does not reproduce the experimental plasma rate coefficients well. Above 2×104 K the agreement between the experimental and theoretical rate coefficients is much better, and the deviations are smaller than the estimated uncertainties.
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| 3. |
- Ali, Safdar, et al.
(author)
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Experimental rate coefficients of F5+ recombining into F4
- 2013
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 557
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Journal article (peer-reviewed)abstract
- Recombination spectra of F5+ producing F4+ have been investigated with high-energy resolution, using the CRYRING heavy-ion storage ring. The absolute recombination rate coefficients are derived in the centre-of-mass energy range of 0-25 eV. The experimental results are compared with intermediate-coupling AUTOSTRUCTURE calculations for 2s-2p (Delta n = 0) core excitation and show very good agreement in the resonance energy positions and intensities. Trielectronic recombination with 2s(2)-2p(2) transitions are clearly identified in the spectrum. Contributions from F5+ ions in an initial metastable state are also considered. The energy-dependent recombination spectra are convoluted with Maxwell-Boltzmann energy distribution in the 10(3)-10(6) K temperature range. The resulting temperature-dependent rate coefficients are compared with theoretical results from the literature. In the 10(3)-10(4) K range, the calculated data significantly underestimates the plasma recombination rate coefficients. Above 8 x 10(4) K, our AUTOSTRUCTURE results and plasma rate coefficients from elsewhere show agreement that is better than 25% with the experimental results.
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| 4. |
- Ali, Safdar, et al.
(author)
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Experimental recombination rate coefficients of Be-like Frecombining into B-like F
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Other publication (other academic/artistic)abstract
- Recombination spectra of F VI forming F V have been investigated with high-energy resolution, using the CRYRING heavy-ion storage ring. The absolute recombination rate coefficients are derived in the center-of-mass energy range of 0-25 eV. The experimental results are compared with intermediate coupling AUTOSTRUCTURE calculations for 2s-2p (∆n=0) core excitation and show a very good agreement in the resonance energy positions and intensities. Trielectronic recombination with 2s2-2p2 transitions are clearly identified in the spectrum. Metastable ion contributions are considered and found negligible. The energy dependent recombination spectra are convoluted with Maxwell-Boltzmann energy distribution in the 10-106 K temperature range. The resulting temperature dependent rate coefficients are compared with theoretical results from literature. In the 103-104 K range the calculated data significantly underestimates the plasma recombination rate coefficients. Above ~105 K, our AUTOSTRUCTURE results and plasma rate coefficients from Colgan et al. (2003) show an agreement better than 20% with the experimental results.
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| 5. |
- Ali, Safdar, et al.
(author)
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Photo-recombination studies at R-EBIT with a Labview control and data = quisition system
- 2011
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In: Journal of Instrumentation. - 1748-0221. ; 6, s. C01016-
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Journal article (peer-reviewed)abstract
- Equipment at the Stockholm Refrigerated Electron Beam Ion Trap (R-EBIT) was developed for photo-recombination studies. A LabView-based event mode data acquisition and R-EBIT control system was implemented. The energies of KLL dielectronic recombination resonances in Li- to C-like argon ions were determined and compared with theoretical calculations performed using a distorted wave approximation. The theoretical and experimental peak positions for Li-, Be-, and C-like argon ions agree within the error bars. For B-like argon we observe an energy shift of 9 eV between the experimentally obtained peak position and the calculated result.
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| 6. |
- Böhm, Sebastian, et al.
(author)
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First results from the Stockholm Electron Beam Ion Trap
- 2007
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In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 58:303, s. 303-306
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Journal article (peer-reviewed)abstract
- A new laboratory for highly charged ions is being built up at Stockholm university. An electron beam ion trap (EBIT) (3T magnet,≤30 keV electron beam) was installed. It is used for spectroscopic studies, precision mass measurements, electron ion collisions, and highlycharged ion surface studies. Here we report about a fast ion-extraction scheme from ebit and first results using a time-of-flight detection as well as a labview based operational system of ebit.
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| 7. |
- Gumberidze, A., et al.
(author)
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Electron- and Proton-Impact Excitation of Hydrogenlike Uranium in Relativistic Collisions
- 2013
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 110:21, s. 213201-
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Journal article (peer-reviewed)abstract
- The K shell excitation of H-like uranium (U91+) in relativistic collisions with different gaseous targets has been studied at the experimental storage ring at GSI Darmstadt. By performing measurements with different targets as well as with different collision energies, we were able to observe for the first time the effect of electron-impact excitation (EIE) process in the heaviest hydrogenlike ion. The large fine-structure splitting in H-like uranium allowed us to unambiguously resolve excitation into different L shell levels. State-of-the-art calculations performed within the relativistic framework which include excitation mechanisms due to both protons (nucleus) and electrons are in good agreement with the experimental findings. Moreover, our experimental data clearly demonstrate the importance of including the generalized Breit interaction in the treatment of the EIE process.
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| 8. |
- Hobein, Matthias, 1981-, et al.
(author)
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Optimization of the Stockholm R-EBIT for the production and extraction of highly charged ions
- 2010
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In: Journal of Instrumentation. - 1748-0221. ; 5:C11003
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Journal article (peer-reviewed)abstract
- We describe a refrigerated EBIT (R-EBIT) commissioned at the AlbaNova Research Center at Stockholm University. As an innovative solution, the superconducting magnet and the trapping drift tubes of the R-EBIT are cooled to a temperature of 4 K by a set of two cooling heads connected to helium compressors. This dry, i.e. liquid helium and liquid nitrogen free, system is easily operated and creates highly charged ions at a fraction of the cost of traditional liquid-cooled systems. A pulsed and continuous gas injection system was developed to feed neutral particles into the electron beam in the trap region. This improves significantly the highly charged ion production and R-EBIT performance. Fast extraction of ions from the R-EBIT yields very short ( < 100 ns), charge-separated ion bunches which can be either analysed using a straight time-of-flight section or sent to experimental beam lines following selection in a bending magnet. An emittance meter was used to measure the emittance of the ions extracted from the R-EBIT. The extracted ions were also re-trapped in a cylindrical Penning trap and properties of the re-trapped ions have been measured using the emittance meter. Results of these measurements are reported in this publication.
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| 9. |
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| 10. |
- Lindroth, Eva, et al.
(author)
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Electron-impact recombination and excitation rates for charge-state-selected highly charged Si ions
- 2020
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 101:6
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Journal article (peer-reviewed)abstract
- Charge-state selective recombination rate coefficients were measured by time of flight (TOF) analyzed highly charged Si ions extracted from an electron-beam ion trap. Additionally, the combination of simultaneous TOF and x-ray measurements and a separation of the dielectronic recombination contribution in the x-ray spectra is used for extracting electron-impact excitation rate coefficients for several overlaying charge states. Experimentally derived dielectronic recombination spectra for XIII and XIV Si are compared and found in excellent agreement with the results of relativistic many-body perturbation theory calculations.
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