Person: ALTUN, ZİKRİ
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ALTUN
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ZİKRİ
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Publication Open Access Dielectronic recombination data for dynamic finite-density plasmas - VI. The boron isoelectronic sequence(EDP SCIENCES S A, 2004-06) YUMAK YAHŞİ, AYŞE; Altun, Z; Yumak, A; Badnell, NR; Colgan, J; Pindzola, MSWe have calculated dielectronic recombination rate coefficients for 22 ions of the boron isoelectronic sequence, between C+ and Xe49+, within the generalized collisional-radiative framework, as outlined by Badnell et al. (2003). Calculations have been performed from both ground and metastable initial states, in both LS- and intermediate-coupling, allowing for Deltan = 0 and Deltan = 1 core-excitations. Results are presented and discussed for a selection of ions from the sequence. Results which are not presented here can be accessed from the Atomic Data and Analysis Structure (ADAS) database (Summers 2003) or from the Oak Ridge Controlled Fusion Atomic Data Center (http://www-cfadc.phy.ornl.gov). Comparison is made with the results of other existing theoretical calculations.Publication Open Access Determination of the recombination rate coefficients for Na-like SiIV forming Mg-like SiIII(EDP SCIENCES S A, 2006-11) ALTUN, ZİKRİ; Orban, I.; Glans, P.; Altun, Z.; Lindroth, E.; Kallberg, A.; Schuch, R.Aims. Absolute, total recombination rate coefficients for Si IV were determined using the CRYING heavy-ion storage ring. Calculated rate coefficients were used to estimate recombination into states that could not be detected in the experiment because of 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 ions were 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. Delta n = 0 core excitations up to the 3s -> 3d series limit. The results of an intermediate coupling AUTOSTRUCTURE calculation were compared with the experiment. The theoretical results were also used to estimate the contribution to dielectronic recombination by high Rydberg states, which were not detected because of field ionization. The spectra were convoluted with Maxwell-Boltzmann energy distributions in the 10(3)-10(6) K temperature range. Results. The resulting plasma recombination rate coefficients are presented and compared with theoretical results frequently used for plasma modeling. In the 10(3)-10(4) K range, a significant underestimation of the calculated dielectronic recombination plasma rate coefficients was observed. Above 3 x 104 K, the agreement between our dielectronic recombination plasma rate coefficients and two of the previously published rate coefficients is better than 20%. Conclusions. The observed differences between the experimental and calculated recombination rate coefficients at low temperatures reflect the need for benchmarking experiments. Our experimentally-derived rate coefficients can guide the development of better theoretical models and lead to more accurately-calculated rate coefficients.Publication Open Access Dielectronic recombination data for dynamic finite-density plasmas - XIII. The magnesium isoelectronic sequence(EDP SCIENCES S A, 2007-11) YUMAK YAHŞİ, AYŞE; Altun, Z.; Yumak, A.; Yavuz, I.; Badnell, N. R.; Loch, S. D.; Pindzola, M. S.We have calculated total and partial final- state level- resolved dielectronic recombination ( DR) rate coe. cients for the ground and metastable initial levels of 21 Mg- like ions between Al+ and Xe42+. This is the final part of the assembly of a levelresolved DR database necessary for modelling dynamic finite-density plasmas within the generalized collisional-radiative framework. Calculations have been performed in both LS-and intermediate coupling, allowing for. n = 0 and. n = 1 core- excitations from ground and metastable levels. Complementary partial and total radiative recombination RR coeficients have been calculated for the same ions viz. Al+ through Zn18+, as well as Kr24+, Mo30+, and Xe42+. Fitting coeficients which describe the total RR and DR rate coeficients (separately) are also presented here. Results for a selection of ions fromthis sequence are discussed, and compared with existing theoretical and experimental results. A full set of results can be accessed from the Atomic Data and Analysis Structure (ADAS) database or from the Oak Ridge Controlled Fusion Atomic Data Center (http://www-cfadc.phy.ornl.gov/data_and_codes). The complexity of further M-shell sequences, both from the atomic and modelling perspectives, renders this juncture a natural conclusion for the assemblage of the partial database. Further M-shell work, has and will, focus more on total rate coe. cients, rather than partials, at least in the medium term.Publication Open Access Dielectronic recombination of Fe xv forming Fe xiv: Laboratory measurements and theoretical calculations(IOP PUBLISHING LTD, 2007-08) ALTUN, ZİKRİ; Lukic, D. V.; Schnell, M.; Savin, D. W.; Brandau, C.; Schmidt, E. W.; Boehm, S.; Mueller, A.; Schippers, S.; Lestinsky, M.; Sprenger, F.; Wolf, A.; Altun, Z.; Badnell, N. R.We have measured resonance strengths and energies for dielectronic recombination (DR) of Mg-like Fe xv forming Al-like Fe XIV via N = 3 -> N' = 3 core excitations in the electron-ion collision energy range 0 - 45 eV. All measurements were carried out using the heavy-ion test storage ring at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We have also carried out new multiconfiguration Breit-Pauli (MCBP) calculations using the AUTOSTRUCTURE code. For electron-ion collision energies less than or similar to 25 eV we find poor agreement between our experimental and theoretical resonance energies and strengths. From 25 to 42 eV we find good agreement between the two for resonance energies. But in this energy range the theoretical resonance strengths are approximate to 31% larger than the experimental results. This is larger than our estimated total experimental uncertainty in this energy range of +/- 26% ( at a 90% confidence level). Above 42 eV the difference in the shape between the calculated and measured 3s3p(P-1(1))nl DR series limit we attribute partly to the nl dependence of the detection probabilities of high Rydberg states in the experiment. We have used our measurements, supplemented by our AUTOSTRUCTURE calculations, to produce a Maxwellian-averaged 3 -> 3 DR rate coefficient for Fe XV forming Fe XIV. The resulting rate coefficient is estimated to be accurate to better than +/- 29% (at a 90% confidence level) for k(B)T(e) >= 1 eV. At temperatures of kBTe >= 2.5 - 15 eV, where Fe XV is predicted to form in photoionized plasmas, significant discrepancies are found between our experimentally derived rate coefficient and previously published theoretical results. Our new MCBP plasma rate coefficient is 19% Y28% smaller than our experimental results over this temperature range.