Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Electron - Ion Recombination Studies of Astrophysically Relevant Ions: Storage Ring and Electron Beam Ion Trap Based Measurements
Stockholm University, Faculty of Science, Department of Physics. (Atomic Physics)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis contains experimental work that was performed at two state-of-the art devices for electron-ion collision physics, at a heavy-ion storage ring and at an Electron Beam Ion Trap. As a result, absolute recombination rate coefficients for H-like Si, He-like Si, Be-like Si, and Na-like Si, as well as Be-like Ne, Na-like S and Na-like Ar are reported over a wide energy range from μeV to keV. The experimentally derived recombination spectra are compared with results of Many Body Perturbation Theory calculations and AUTOSTRUCTURE calculations. Furthermore, the effect of external electric fields on the recombination rate is investigated for two Na-like ions, and a strong enhancement of dielectronic recombination into high Rydberg states is observed. Experimental plasma rate coefficients are derived for the studied ions for the first time and are compared with calculated values available in the literature. In the EBIT experiment, a novel extraction method provides complete charge state spectra of the ions for every extraction. Absolute DR rate coefficients for both H-like Si and He-like Si are obtained from the same measurement. Comparison with recorded X-ray spectra enables the separation of the photon spectra arising from charge-changing and charge-preserving reactions and facilitates the extraction of electron impact excitation rate coefficients.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2009. , 150 p.
Keyword [en]
atomic processes, electron-ion recombination, plasma
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-33254ISBN: 978-91-7155-989-0 (print)OAI: oai:DiVA.org:su-33254DiVA: diva2:282779
Public defence
2010-01-29, sal FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 14:30 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 6: Submitted. Paper 7: Submitted. Available from: 2010-01-07 Created: 2009-12-21 Last updated: 2010-01-08Bibliographically approved
List of papers
1. Determination of the recombination rate coefficients for Na-like Si IV forming Mg-like Si III
Open this publication in new window or tab >>Determination of the recombination rate coefficients for Na-like Si IV forming Mg-like Si III
Show others...
2006 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 459, no 1, 291-296 p.Article in journal (Refereed) Published
Abstract [en]

Aims. Absolute, total recombination rate coefficients for Si iv were determined using the CRYRING heavy-ion storage ring.Calculated rate coefficients were used to estimate recombination into states that could not be detected in the experiment becauseof field ionization. Total, as well as separate, radiative and dielectronic plasma recombination rate coefficients were determined.Methods. Stored ions were merged with an expanded electron beam in the electron cooler section of the storage ring. Recombined ionswere separated from the stored ion beam in the first dipole magnet after the electron cooler and were detected with unity efficiency.The absolute radiative and dielectronic recombination rate coefficients were obtained over a center-of-mass energy range of 0−20 eV,covering Δn = 0 core excitations up to the 3s → 3d series limit. The results of an intermediate coupling autostructure calculationwere compared with the experiment. The theoretical results were also used to estimate the contribution to dielectronic recombinationby high Rydberg states, which were not detected because of field ionization. The spectra were convoluted with Maxwell-Boltzmannenergy distributions in the 103−106 K temperature range.Results. The resulting plasma recombination rate coefficients are presented and compared with theoretical results frequently usedfor plasma modeling. In the 103−104 K range, a significant underestimation of the calculated dielectronic recombination plasma ratecoefficients was observed. Above 3 × 104 K, the agreement between our dielectronic recombination plasma rate coefficients and twoof the previously published rate coefficients is better than 20%.Conclusions. The observed differences between the experimental and calculated recombination rate coefficients at low temperaturesreflect the need for benchmarking experiments. Our experimentally-derived rate coefficients can guide the development of bettertheoretical models and lead to more accurately-calculated rate coefficients.

Keyword
atomic data, atomic processes, plasmas
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-12367 (URN)10.1051/0004-6361:20054660 (DOI)
Available from: 2009-01-15 Created: 2009-01-15 Last updated: 2017-12-13Bibliographically approved
2. Spectroscopic study of doubly excited states in Mg-like Si using dielectronic recombination
Open this publication in new window or tab >>Spectroscopic study of doubly excited states in Mg-like Si using dielectronic recombination
2007 (English)In: Journal of Physics B, Vol. 40, 1063- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-12390 (URN)
Available from: 2008-01-15 Created: 2008-01-15 Last updated: 2011-01-11Bibliographically approved
3. Experimental dielectronic recombination rate coefficientsfor Na-like S VI and Na-like Ar VIII
Open this publication in new window or tab >>Experimental dielectronic recombination rate coefficientsfor Na-like S VI and Na-like Ar VIII
Show others...
2009 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 498, 909-914 p.Article in journal (Refereed) Published
Abstract [en]

Aims. Absolute recombination rate coefficients for two astrophysically relevant Na-like ions are presented.Methods. Recombination rate coefficients of S vi and Ar viii are determined from merged-beam type experiments at the CRYRINGelectron cooler. Calculated rate coefficients are used to account for recombination into states that are field-ionized and therefore notdetected in the experiment.Results. Dielectronic recombination rate coefficients were obtained over an energy range covering Δ n = 0 core excitations. ForNa-like Ar a measurement was also performed over the Δn = 1 type of resonances. In the low-energy part of the Ar viii spectrum,enhancements of more than one order of magnitude are observed as compared to the calculated radiative recombination. The plasmarecombination rate coefficients of the two Na-like ions are compared with calculated results from the literature. In the 103−104 Krange, large discrepancies are observed between calculated plasma rate coefficients and our data. At higher temperatures, above105 K, in the case of both ions our data is 30% higher than two calculated plasma rate coefficients, other data from the literaturehaving even lower values.Conclusions. Discrepancies below 104 K show that at such temperatures even state-of-the-art calculations yield plasma rate coefficientsthat have large uncertainties. The main reason for these uncertainties are the contributions from low-energy resonances, whichare difficult to calculate accurately.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-33223 (URN)10.1051/0004-6361/200911799 (DOI)000266121800027 ()
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2017-12-12Bibliographically approved
4. Recombination rate coefficients of Be-like neon
Open this publication in new window or tab >>Recombination rate coefficients of Be-like neon
2008 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 489, no 2, 829-835 p.Article in journal (Refereed) Published
Abstract [en]

Aims. Merged-beam and plasma recombination rate coefficients for Be-likeNe vii were extracted from results of a merged-beam typeexperiment.Methods. The cryring heavy-ion storage ring was used to determine merged-beam recombination rate coefficients for Be-likeNe6+.Recombined Ne5+ ions were separated from the stored beam in the first dipole magnet following the electron-ion interaction region.Field-ionization at this dipole magnet prevented detection of recombination into states with the principal quantum number n > ncutoff =23. To account for the field-ionization effects, results obtained with autostructure calculations were used for recombinationchannels above ncutoff. The merged-beam recombination rate coefficients were then convoluted with Maxwellian electron energydistributions in the 103−3 × 106 K temperature region, to obtain plasma recombination rate coefficients.Results. Good agreement was found between the experimentally derived rate coefficient spectrum and results of the autostructurecalculation. At low energies, several strong dielectronic recombination resonances belonging to the spin-forbidden 2s2p(3PJ)nl seriesdominate the merged-beam spectrum. Recombination through these states dominates at low-temperatures, e.g. at 103 K recombinationthrough these resonances is more than one order of magnitude higher than the radiative recombination rate coefficient. Most data fromthe literature significantly underestimate the low-temperature plasma rate coefficients below 104 K, with only two calculations showingrate coefficients comparable to our results.Strong contributions from trielectronic recombination were found in the merged-beam spectrum of Be-like Ne, associated with doubleexcitation of the Be-likeNe core, during the attachment of the free electron. Calculated trielectronic recombination resonance positionsagree with experimental peaks, however compared to the experiment, the calculation underestimates the strength of trielectronicrecombination.

Keyword
atomic data, atomic processes, line: formation, plasmas, Sun: general
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-33244 (URN)10.1051/0004-6361:200810295 (DOI)000259601500046 ()
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2017-12-12Bibliographically approved
5. DIELECTRONIC RECOMBINATION OF Na-LIKE S AND Na-LIKE Ar IN THE PRESENCE OF EXTERNAL FIELDS
Open this publication in new window or tab >>DIELECTRONIC RECOMBINATION OF Na-LIKE S AND Na-LIKE Ar IN THE PRESENCE OF EXTERNAL FIELDS
2009 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 694, no 1, 354-358 p.Article in journal (Refereed) Published
Abstract [en]

Recombination rate coefficients for two astrophysically relevant Na-like ions, S5+ and Ar7+, were derived frommeasurements at the electron cooler device of the CRYRING heavy-ion storage ring. Additionally, the enhancementof dielectronic recombination (DR) by external fields was studied for these ions. Motional electric fields wereinduced over the electron–ion interaction region by tilting the magnetic field that guides the electrons on thetrajectory of the circulating ions. Field ionization at the dipole magnet prevented the detection of ions recombinedinto high Rydberg states. By comparing integrated areas of the recombination spectra over the field-affected range,enhancement factors of up to 1.9 and 2 were observed in the case of S5+ and Ar7+, for the maximum appliedfields of ∼184 V cm−1 and ∼172 V cm−1, respectively. Saturation was not reached and at higher fields even higherenhancements are to be expected. Plasma DR rate coefficients were obtained from the experimental spectra recordedat different field strengths. For the highest applied fields, increasing enhancement of the plasma DR rates was foundwith higher temperatures, reaching up to ∼42% and ∼73% at 106 K, in the case of S5+ and Ar7+, respectively.

Keyword
atomic data – atomic processes – magnetic fields – plasmas
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-33230 (URN)10.1088/0004-637X/694/1/354 (DOI)000264291700035 ()
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2017-12-12Bibliographically approved
6. Recombination rate coefficients of Be-like Si
Open this publication in new window or tab >>Recombination rate coefficients of Be-like Si
2010 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 721, no 2, 1603-1607 p.Article in journal (Refereed) Published
Abstract [en]

Recombination rate coefficients for Be-like Si10+ recombining into B-like Si9+ are derived froma measurement at an electron cooler device. The recombination spectrum shows strong contributionsfrom trielectronic recombination. Below 100 meV several very strong resonances associatedwith a spin-flip of the excited electron dominate the spectrum and also dominate thelow-temperature plasma recombination rate coefficents. Calculated rate coefficients are used toestimate the metastable fraction of the ion beam in the experiment and are also used to estimatethe amount of recombined ions that were not detected in the experiment, because of fieldionization. The resonant plasma rate coefficients corrected for the experimental field ionizationare in good agreement with calculated results by Gu (2003) and with AUTOSTRUCTURE calculations.All other calculations significantly underestimate the plasma rate coefficients at lowtemperatures.

Keyword
atomic data, atomic processes, plasmas
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-33248 (URN)10.1088/0004-637X/721/2/1603 (DOI)
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2017-12-12Bibliographically approved
7. Charge-state Selected Detection of Photons from Electron-Ion Interactions in an EBIT
Open this publication in new window or tab >>Charge-state Selected Detection of Photons from Electron-Ion Interactions in an EBIT
Show others...
2009 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114Article in journal (Refereed) Submitted
Abstract [en]

A new approach provides charge-state selective recombination rate coefficients from TOF spectraof highly charged ions extracted from an EBIT. Experimentally derived dielectronic recombinationspectra are compared with results of relativistic many body perturbation theory calculations. Electronimpact excitation rate coefficients are also obtained from the experiment through the separationof the DR contribution in the X-ray spectra. The combination of TOF and X-ray measurementsoffers a powerful tool for the simultaneous extraction of atomic quantities for several charge states.

National Category
Dentistry Physical Sciences
Identifiers
urn:nbn:se:su:diva-33209 (URN)
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2017-12-12Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Orban, Istvan
By organisation
Department of Physics
Physical Sciences

Search outside of DiVA

GoogleGoogle Scholar

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 411 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf