Academic Commons Search Results
http://academiccommons.columbia.edu/catalog.rss?f%5Bsubject_facet%5D%5B%5D=Atomic+physics&q=&rows=500&sort=record_creation_date+desc
Academic Commons Search Resultsen-usAn atom trap trace analysis (ATTA) system for measuring ultra-low contamination by krypton in xenon dark matter detectors
http://academiccommons.columbia.edu/catalog/ac:166773
Yoon, Taehyunhttp://hdl.handle.net/10022/AC:P:22057Thu, 31 Oct 2013 00:00:00 +0000The XENON dark matter experiment aims to detect hypothetical weakly interacting massive particles (WIMPs) scattering off nuclei within its liquid xenon (LXe) target. The trace 85Kr in the xenon target undergoes beta-decay with a 687 keV end point and 10.8 year halflife, which contributes background events and limits the sensitivity of the experiment. In order to achieve the desired sensitivity, the contamination by krypton is reduced to the part per trillion (ppt) level by cryogenic distillation. The conventional methods are not well suited for measuring the krypton contamination at such a low level. In this work, we have developed an atom trap trace analysis (ATTA) device to detect the ultra-low krypton concentration in the xenon target. This project was proposed to the National Science Foundation (NSF) as a Major Research Instrumentation (MRI) development [Aprile and Zelevinsky, 2009] and is funded by NSF and Columbia University. The ATTA method, originally developed at Argonne National Laboratory, uses standard laser cooling and trapping techniques, and counts single trapped atoms. Since the isotopic abundance of 85Kr in nature is 1.5 × 10^-11, the 85Kr/Xe level is expected to be ~10^-23, which is beyond the capability of our method. Thus we detect the most abundant (57%) isotope 84Kr, and infer the 85Kr contamination from their known abundances. To avoid contamination by krypton, the setup is tested and optimized with 40Ar which has a similar cooling wavelength to 84Kr. Two main challenges in this experiment are to obtain a trapping efficiency high enough to detect krypton impurities at the ppt level, and to achieve the resolution to discriminate single atoms. The device is specially designed and adjusted to meet these challenges. After achieving these criteria with argon gas, we precisely characterize the efficiency of the system using Kr-Xe mixtures with known ratios, and find that ~90 minutes are required to trap one 84Kr atom at the 1-ppt Kr/Xe contamination. This thesis describes the design, construction, and experimental results of the ATTA project at Columbia University.Atomic physics, Astrophysicsty2182PhysicsDissertationsLifshitz theory of van der Waals pressure in dissipative media
http://academiccommons.columbia.edu/catalog/ac:166217
Zheng, Yi; Narayanaswamy, Arvindhttp://hdl.handle.net/10022/AC:P:21926Thu, 03 Oct 2013 00:00:00 +0000We derive a first-principles method of determining the van der Waals or Casimir pressure in a dissipative and dispersive planar multilayered system by calculating the Maxwell stress tensor in a fictitious layer of vacuum, that is eventually made to vanish, introduced in the structure. This is illustrated by calculating the van der Waals pressure in a thin film with dissipative properties embedded between two semi-infinite media.Mechanical engineering, Atomic physics, Molecular physicsyz2308, an2288Mechanical EngineeringArticlesHigh-resolution nanomechanical analysis of suspended electrospun silk fibers with the torsional harmonic atomic force microscope
http://academiccommons.columbia.edu/catalog/ac:163061
Cronin-Golomb, Mark; Sahin, Ozgurhttp://hdl.handle.net/10022/AC:P:21006Thu, 11 Jul 2013 00:00:00 +0000Atomic force microscopes have become indispensable tools for mechanical characterization of nanoscale and submicron structures. However, materials with complex geometries, such as electrospun fiber networks used for tissue scaffolds, still pose challenges due to the influence of tension and bending modulus on the response of the suspended structures. Here we report mechanical measurements on electrospun silk fibers with various treatments that allow discriminating among the different mechanisms that determine the mechanical behavior of these complex structures. In particular we were able to identify the role of tension and boundary conditions (pinned versus clamped) in determining the mechanical response of electrospun silk fibers. Our findings show that high-resolution mechanical imaging with torsional harmonic atomic force microscopy provides a reliable method to investigate the mechanics of materials with complex geometries.Nanotechnology, Materials science, Atomic physicsos2246Biological SciencesArticlesSoliton dynamics in the multiphoton plasma regime
http://academiccommons.columbia.edu/catalog/ac:163155
Husko, Chad A.; Combrie, Sylvain; Colman, Pierre; Zheng, Jiangjun; De Rossi, Alfredo; Wong, Chee Weihttp://hdl.handle.net/10022/AC:P:21037Thu, 11 Jul 2013 00:00:00 +0000Solitary waves have consistently captured the imagination of scientists, ranging from fundamental breakthroughs in spectroscopy and metrology enabled by supercontinuum light, to gap solitons for dispersionless slow-light, and discrete spatial solitons in lattices, amongst others. Recent progress in strong-field atomic physics include impressive demonstrations of attosecond pulses and high-harmonic generation via photoionization of free-electrons in gases at extreme intensities of 1014 W/cm2. Here we report the first phase-resolved observations of femtosecond optical solitons in a semiconductor microchip, with multiphoton ionization at picojoule energies and 1010 W/cm2 intensities. The dramatic nonlinearity leads to picojoule observations of free-electron-induced blue-shift at 1016 cm−3 carrier densities and self-chirped femtosecond soliton acceleration. Furthermore, we evidence the time-gated dynamics of soliton splitting on-chip, and the suppression of soliton recurrence due to fast free-electron dynamics. These observations in the highly dispersive slow-light media reveal a rich set of physics governing ultralow-power nonlinear photon-plasma dynamics.Mechanical engineering, Atomic physicscah2116, jz2356, cww2104Mechanical EngineeringArticlesCalculation of Atomic Data for NASA Missions
http://academiccommons.columbia.edu/catalog/ac:158806
Savin, Daniel Wolf; Gorczyca, T. W.; Fu, J.; Korista, K. T.; Nikolic, D.; Hasoǧlu, M. F.; Dumitriu, I.; Badnell, N. R.; Manson, S. T.http://hdl.handle.net/10022/AC:P:19659Fri, 05 Apr 2013 00:00:00 +0000The interpretation of cosmic spectra relies on a vast sea of atomic data which are not readily obtainable from analytic expressions or simple calculations. Rather, their evaluation typically requires state-of-the-art atomic physics calculations, with the inclusion of weaker effects (spin-orbit and configuration interactions, relaxation, Auger broadening, etc.), to achieve the level of accuracy needed for use by astrophysicists. Our NASA-supported research program is focused on calculating data for three important atomic processes, 1) dielectronic recombination (DR), 2) inner-shell photoabsorption, and 3) fluorescence and Auger decay of inner-shell vacancy states. Some additional details and examples of our recent findings are given below.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsPresentationsCollisional Ionization Equilibrium for Optically Thin Plasmas
http://academiccommons.columbia.edu/catalog/ac:158803
Savin, Daniel Wolf; Bryans, P.; Mitthumsiri, W.; Badnell, N. R.; Gorczyca, T. W.; Laming, J. M.http://hdl.handle.net/10022/AC:P:19658Fri, 05 Apr 2013 00:00:00 +0000Reliably interpreting spectra from electron-ionized cosmic plasmas requires accurate ionization balance calculations for the plasma in question. However, much of the atomic data needed for these calculations have not been generated using modern theoretical methods and their reliability are often highly suspect. We have utilized state-of-the-art calculations of dielectronic recombination (DR) rate coefficients for the hydrogenic through Na-like ions of all elements from He to Zn. We have also utilized state-of-the-art radiative recombination (RR) rate coefficient calculations for the bare through Na-like ions of all elements from H to Zn. Using our data and the recommended electron impact ionization data of Mazzotta et al. (1998), we have calculated improved collisional ionization equilibrium calculations. We compare our calculated fractional ionic abundances using these data with those presented by Mazzotta et al. (1998) for all elements from H to Ni, and with the fractional abundances derived from the modern DR and RR calculations of Gu (2003a,b, 2004) for Mg, Si, S, Ar, Ca, Fe, and Ni.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsPresentationsPrecision measurement of the lifetime of the 1s2s3S1 metastable level in heliumlike O6+
http://academiccommons.columbia.edu/catalog/ac:158672
Savin, Daniel Wolf; Lopez-Urrutia, J. R. Crespo; Beiersdorfer, P.; Widmann, K.http://hdl.handle.net/10022/AC:P:19544Fri, 29 Mar 2013 00:00:00 +0000The lifetime of the 1s2s3S1 level of the He-like O6+ ion has been measured using the Electron Beam Ion Trap in the magnetic trapping mode. A value of 956-4+5 μs is found, which corresponds to a radiative transition rate of 1046-5+4 s-1 for the magnetic dipole transition to the 1s21S0 ground state. This value is in excellent agreement with recent theoretical predictions and distinguishes among different treatments of negative energy states and correlation in multiconfiguration Dirac-Fock calculations.Astrophysics, Atomic physics, Plasma physicsdws26Astronomy and AstrophysicsArticlesElectron capture by Ne2+ ions from atomic hydrogen
http://academiccommons.columbia.edu/catalog/ac:158696
Savin, Daniel Wolf; Mroczkowski, T.; Rejoub, R.; Krstic, P. S.; Havener, C. C.http://hdl.handle.net/10022/AC:P:19549Fri, 29 Mar 2013 00:00:00 +0000Using a merged-beam technique, the absolute, total electron-capture cross section has been measured for collisions of Ne2+ ions with hydrogen (deuterium) atoms at collision energies between 139 and 1490 eV/u. These data are compared to three other published measurements, two of which differ from one another by a factor greater than two. Early quantal rate coefficient calculations for Ne2+ ions with hydrogen at eV/u energies predict a cross section many orders of magnitude below the previously measured cross section at 40 eV/u. A possible explanation is given for the discrepancy between theory and experiment.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesElectron capture by Ne3+ ions from atomic hydrogen
http://academiccommons.columbia.edu/catalog/ac:158699
Savin, Daniel Wolf; Rejoub, R.; Havener, C. C.; Bannister, M. E.; Verzani, C. J.; Wang, J. G.; Stancil, P. C.http://hdl.handle.net/10022/AC:P:19550Fri, 29 Mar 2013 00:00:00 +0000Using the Oak Ridge National Laboratory ion-atom merged-beam apparatus, absolute total electron-capture cross sections have been measured for collisions of Ne3+ ions with hydrogen (deuterium) atoms at energies between 0.07 and 826 eV∕u. Comparison to previous measurements shows large discrepancies between 50 and 400 eV∕u. Previously published molecular-orbital close-coupling (MOCC) calculations were performed over limited energy ranges, but show good agreement with the present measurements. Here MOCC calculations are presented for energies between 0.01 and 1000 eV∕u for collisions with both H and D. For energies below ∼1 eV∕u, an enhancement in the magnitude of both the experimental and theoretical cross sections is observed which is attributed to the ion-induced dipole attraction between the reactants. Below ∼4 eV∕u, the present calculations show a significant target isotope effect.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesA novel merged beams apparatus to study anion-neutral reactions
http://academiccommons.columbia.edu/catalog/ac:158711
Savin, Daniel Wolf; Bruhns, H. ; Kreckel, H.; Miller, Kenneth; Lestinsky, M.; Seredyuk, B.; Mitthumsiri, W.; Schmitt, B. L.; Schnell, M.; Urbain, X.; Rappaport, M. L.; Havener, C. C.http://hdl.handle.net/10022/AC:P:19553Fri, 29 Mar 2013 00:00:00 +0000We have developed a novel laboratory instrument for studying gas phase, anion-neutral chemistry. To the best of our knowledge, this is the first such apparatus which uses fast merged beams to investigate anion-neutral chemical reactions. As proof-of-principle we have detected the associative detachment reaction H−+H→H2+e−. Here we describe the apparatus in detail and discuss related technical and experimental issues.Astrophysics, Plasma physics, Atomic physicsdws26, kam2211Astronomy and AstrophysicsArticlesShortcomings of the R-matrix method for treating dielectronic recombination
http://academiccommons.columbia.edu/catalog/ac:158705
Savin, Daniel Wolf; Gorczyca, T. W.; Badnell, N. R.http://hdl.handle.net/10022/AC:P:19551Fri, 29 Mar 2013 00:00:00 +0000By performing radiation-damped R-matrix scattering calculations for the photorecombination of Fe17+ forming Fe16+, we demonstrate and discuss the difficulties and fundamental inaccuracies associated with the R-matrix method for treating dielectronic recombination (DR). Our R-matrix results significantly improve upon earlier R-matrix results for this ion. However, we show theoretically that all R-matrix methods are unable to account accurately for the phenomenon of radiative decay followed by autoionization. For Fe17+, we demonstrate numerically that this results in an overestimate of the DR cross section at the series limit, which tends to our analytically predicted amount of 40%. We further comment on the need for fine resonance resolution and the inclusion of radiation damping effects. Overall, slightly better agreement with experiment is still found with the results of perturbative calculations, which are computationally more efficient than R-matrix calculations by more than two orders of magnitude.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesFe15+ dielectronic recombination and the effects of configuration interaction between resonances with different captured electron principal quantum numbers
http://academiccommons.columbia.edu/catalog/ac:158735
Savin, Daniel Wolf; Kwon, D. H.http://hdl.handle.net/10022/AC:P:19543Fri, 29 Mar 2013 00:00:00 +0000Dielectronic recombination (DR) of Na-like Fe15+ forming Mg-like Fe14+ via excitation of a 2l core electron has been investigated. We find that configuration interaction (CI) between DR resonances with different captured electron principal quantum numbers n can lead to a significant reduction in resonance strengths for n≥5. Previous theoretical work for this system has not considered this form of CI. Including it accounts for most of the discrepancy between previous theoretical and experimental results.Astrophysics, Atomic physics, Plasma physicsdws26Astronomy and AstrophysicsArticlesElectron capture by Ne4+ ions from atomic hydrogen
http://academiccommons.columbia.edu/catalog/ac:158258
Savin, Daniel Wolf; Havener, C. C.; Rejoub, R.; Vane, C. R.; Krause, H. F.; Schnell, M.; Wang, J. G.; Stancil, P. C.http://hdl.handle.net/10022/AC:P:19510Wed, 27 Mar 2013 00:00:00 +0000Using the Oak Ridge National Laboratory ion-atom merged-beams apparatus, the absolute total electron-capture cross section has been measured for collisions of Ne4+ with hydrogen and deuterium at relative energies in the center-of-mass frame between 0.10 and 1006 eV/u. Comparison with previous measurements shows large discrepancies between 80 and 600 eV/u. For energies below ∼1 eV∕u, a sharply increasing cross section is attributed to the ion-induced dipole attraction between the reactants. Multichannel Landau-Zener calculations are performed between 0.01 and 5000 eV/u and compare well to the measured total cross sections. Below ∼5 eV∕u, the present total cross section calculations show a significant target isotope effect. At 0.01 eV/u, the H:D total cross section ratio is predicted to be ∼1.4 where capture is dominated by transitions into the Ne3+ (2s22p23d) configuration.Astrophysics, Atomic physics, Plasma physicsdws26Astronomy and AstrophysicsArticlesIonization Balance, Chemical Abundances, and the Metagalactic Radiation Field at High Redshift
http://academiccommons.columbia.edu/catalog/ac:158255
Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19508Wed, 27 Mar 2013 00:00:00 +0000We have carried out a series of model calculations of the photoionized intergalactic medium (IGM) to determine the effects on the predicted ionic column densities due to uncertainties in the published dielectronic recombination (DR) rate coefficients. Based on our previous experimental work and a comparison of published theoretical DR rates, we estimate there is in general a factor of 2 uncertainty in existing DR rates used for modeling the IGM. We demonstrate that this uncertainty results in factors of ~1.9 uncertainty in the predicted N V and Si IV column densities, ~2.0 for O VI, and ~1.7 for C IV. We show that these systematic uncertainties translate into a systematic uncertainty of up to a factor of ~3.1 in the Si/C abundance ratio inferred from observations. The inferred IGM abundance ratio could thus be less than (Si/C)☉ or greater than 3(Si/C)☉. If the latter is true, then it suggests the metagalactic radiation field is not due purely to quasars but includes a significant stellar component. Lastly, column density ratios of Si IV to C IV versus C II to C IV are often used to constrain the decrement in the metagalactic radiation field at the He II absorption edge. We show that the variation in the predicted Si IV to C IV ratio due to a factor of 2 uncertainty in the DR rates is almost as large as that due to a factor of 10 change in the decrement. Laboratory measurements of the relevant DR resonance strengths and energies are the only unambiguous method of removing the effects of these atomic physics uncertainties from models of the IGM.Astrophysics, Atomic physicsdws26Astronomy and AstrophysicsArticlesElectron-ion recombination of Si IV forming Si III: Storage-ring measurement and multiconfiguration Dirac-Fock calculations
http://academiccommons.columbia.edu/catalog/ac:158264
Savin, Daniel Wolf; Schmidt, E. W.; Bernhardt, D.; Muller, A.; Schippers, S.; Fritzsche, S.; Hoffman, J.; Jaroshevich, A. S.; Krantz, C.; Lestinsky, M.; Orlov, D. A.; Wolf, A.; Lukic, D.http://hdl.handle.net/10022/AC:P:19513Wed, 27 Mar 2013 00:00:00 +0000The electron-ion recombination rate coefficient for Si IV forming Si III was measured at the heavy-ion storage-ring TSR. The experimental electron-ion collision energy range of 0–186 eV encompassed the 2p6nln′l′ dielectronic recombination (DR) resonances associated with 3s→nl core excitations, 2s2p63snln′l′ resonances associated with 2s→nl (n=3,4) core excitations, and 2p53snln′l′ resonances associated with 2p→nl (n=3,…,∞) core excitations. The experimental DR results are compared with theoretical calculations using the multiconfiguration Dirac-Fock (MCDF) method for DR via the 3s→3pn′l′ and 3s→3dn′l′(both n′=3,…,6) and 2p53s3ln′l′ (n′=3,4) capture channels. Finally, the experimental and theoretical plasma DR rate coefficients for Si IV forming Si III are derived and compared with previously available results.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesOrbital sensitivity in Mg2+ dielectronic recombination calculations
http://academiccommons.columbia.edu/catalog/ac:158267
Savin, Daniel Wolf; Fu, J.; Gorczyca, T. W.; Nikolic, D.; Badnell, N. R.; Gu, M. F.http://hdl.handle.net/10022/AC:P:19514Wed, 27 Mar 2013 00:00:00 +0000We have investigated the reason for significant discrepancies between the results of two recent, similar computational methods [ Zatsarinny et al. Astron. Astrophys. 426 699 (2004); Gu Astrophys. J. 590 1131 (2003)] for dielectronic recombination (DR) of Mg2+. It is found that the choice of orbital description can lead to discrepancies by as much as a factor of 2 between total peak DR rate coefficients resulting from otherwise-identical computations. These unexpected differences are attributed to the large sensitivity to bound-orbital relaxation and continuum-orbital description effects on the computed radiative and autoionizing transitions arising from accidental cancellation. In order to obviate these effects, an approach, using a separate, nonorthogonal orbital basis for each configuration, is employed to yield a DR rate coefficient that we assess to be more reliable than all earlier published results.Astrophysics, Atomic physicsdws26Astronomy and AstrophysicsArticlesLow-energy electron capture by Ne2+ ions from H(D)
http://academiccommons.columbia.edu/catalog/ac:158261
Savin, Daniel Wolf; Seredyuk, B.; Bruhns, H.; Seely, D. G.; Aliabadi, H.; Galutschek, E.; Havener, C. C.http://hdl.handle.net/10022/AC:P:19511Wed, 27 Mar 2013 00:00:00 +0000Using the Oak Ridge National Laboratory (ORNL) ion-atom merged-beams apparatus, the absolute, total single-electron-capture cross section has been measured for collisions of Ne2+ with deuterium (D) at center-of-mass (c.m.) collision energies of 59–949 eV∕u. With the high-velocity ion beams now available at the ORNL Multicharged Ion Research Facility, we have extended our previous merged-beams measurement to lower c.m. collision energies. The data are compared to all four previously published measurements for Ne2++H(D) which differ considerably from one another at energies ≲600 eV∕u. We are unaware of any published theoretical cross-section data for Ne2++H(D) at the energies studied. Early quantal rate coefficient calculations for Ne2++H at eV/u energies suggest a cross section many orders of magnitude below previous measurements of the cross section at 40 eV∕u which is the lowest collision energy for which experimental results have been published. Here we compare our measurements to recent theoretical electron-capture results for He2++H. Both the experimental and theoretical results show a decreasing cross section with decreasing energy.Astrophysics, Atomic physics, Plasma physicsdws26Astronomy and AstrophysicsArticlesLow-energy charge transfer for collisions of Si3+ with atomic hydrogen
http://academiccommons.columbia.edu/catalog/ac:158270
Savin, Daniel Wolf; Bruhns, H.; Kreckel, H.; Seely, D. G.; Havener, C. C.http://hdl.handle.net/10022/AC:P:19515Wed, 27 Mar 2013 00:00:00 +0000Cross sections of charge transfer for Si3+ ions with atomic hydrogen at collision energies of ≈40–2500 eV/u were carried out using a merged-beam technique at the Multicharged Ion Research Facility at Oak Ridge National Laboratory. The data span an energy range in which both molecular orbital close coupling (MOCC) and classical trajectory Monte Carlo (CTMC) calculations are available. The influence of quantum mechanical effects of the ionic core as predicted by MOCC is clearly seen in our results. However, discrepancies between our experiment and MOCC results toward higher collision energies are observed. At energies above 1000 eV/u good agreement is found with CTMC results.Astrophysics, Atomic physicsdws26Astronomy and AstrophysicsArticlesDielectronic Recombination of Fe XXI and Fe XXII via N = 2→N' = 2 Core Excitations
http://academiccommons.columbia.edu/catalog/ac:158506
Savin, Daniel Wolf; Gwinner, G.; Kahn, S. M.; Grieser, M.; Repnow, R.; Gaathoff, G.; Schwalm, D.; Wolf, A.; Muller, A.; Schippers, S.; Zavodszky, P. A.; Chen, M. H.; Gorczyca, T. W.; Zatsarinny, O.; Gu, M. F.http://hdl.handle.net/10022/AC:P:19451Mon, 25 Mar 2013 00:00:00 +0000We have measured dielectronic recombination (DR) resonance strengths and energies for carbon-like Fe XXI forming Fe XX and for boron-like Fe XXII forming Fe XXI via N = 2 → N' = 2 core excitations. 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 calculated these resonance strengths and energies using three independent, state-of-the-art perturbative techniques: a multiconfiguration Breit-Pauli (MCBP) method using the code AUTOSTRUCTURE, a multiconfiguration Dirac-Fock (MCDF) method, and a relativistic configuration interaction method using the Flexible Atomic Code (FAC). Overall, reasonable agreement is found between our experimental results and our theoretical calculations. The most notable discrepancies tend to occur for relative collision energies ≲ 3 eV. We have used our measured 2 → 2 results to produce Maxwellian-averaged rate coefficients for Fe XXI and Fe XXII. Our experimentally derived rate coefficients are estimated to be accurate to better than ≈20% both for Fe XXI at kBTe > 0.5 eV and for Fe XXII at kBTe >0.001 eV. For these results, we provide fits that are accurate to better than 0.5% for Fe XXI at 0.001 eV ≤ kBTe ≤ 10,000 eV and for Fe XXII at 0.02 eV ≲ kBTe ≤ 10,000 eV. Our fitted rate coefficients are suitable for ionization balance calculations involving Fe XXI and Fe XXII in photoionized plasmas. Previous published Burgess formula and LS-coupling calculations are in poor agreement with our experimentally derived rate coefficients. None of these published calculations reliably reproduce the magnitude or temperature dependence of our experimental results. Our previously published Fe XXI MCDF results are in good agreement with our experimental results for kBTe ≳ 0.07 eV. For both ions in this temperature range our new MCBP, MCDF, and FAC results are in excellent agreement with our experimentally derived rate coefficient.Atomic physics, Astrophysics, Plasma physicsdws26Astronomy and AstrophysicsArticlesDielectronic Recombination (via N = 2 → N' = 2 Core Excitations) and Radiative Recombination of Fe XX: Laboratory Measurements and Theoretical Calculations
http://academiccommons.columbia.edu/catalog/ac:158140
Savin, Daniel Wolf; Kahn, S. M.; Behar, E.; Gwinner, G.; Saghiri, A. A.; Schmitt, M.; Grieser, M.; Repnow, R.; Schwalm, D.; Wolf, A.; Bartsch, T.; Muller, A.; Schippers, S.; Badnell, N. R.; Chen, M. H.; Gorczyca, T. W.http://hdl.handle.net/10022/AC:P:19459Mon, 25 Mar 2013 00:00:00 +0000We have measured the resonance strengths and energies for dielectronic recombination (DR) of Fe XX forming Fe XIX via N = 2 → N' = 2 (ΔN = 0) core excitations. We have also calculated the DR resonance strengths and energies using the AUTOSTRUCTURE, Hebrew University Lawrence Livermore Atomic Code (HULLAC), Multiconfiguration Dirac-Fock (MCDF), and R-matrix methods, four different state-of-the-art theoretical techniques. On average the theoretical resonance strengths agree to within ≲10% with experiment. The AUTOSTRUCTURE, MCDF, and R-matrix results are in better agreement with experiment than are the HULLAC results. However, in all cases the 1 σ standard deviation for the ratios of the theoretical-to-experimental resonance strengths is ≳30%, which is significantly larger than the estimated relative experimental uncertainty of ≲10%. This suggests that similar errors exist in the calculated level populations and line emission spectrum of the recombined ion. We confirm that theoretical methods based on inverse-photoionization calculations (e.g., undamped R-matrix methods) will severely overestimate the strength of the DR process unless they include the effects of radiation damping. We also find that the coupling between the DR and radiative recombination (RR) channels is small. Below 2 eV the theoretical resonance energies can be up to ≈30% larger than experiment. This is larger than the estimated uncertainty in the experimental energy scale (≲0.5% below ≈25 eV and ≲0.2% for higher energies) and is attributed to uncertainties in the calculations. These discrepancies makes DR of Fe XX an excellent case for testing atomic structure calculations of ions with partially filled shells. Above 2 eV, agreement between the theoretical and measured energies improves dramatically with the AUTOSTRUCTURE and MCDF results falling within 2% of experiment, the R-matrix results within 3%, and HULLAC within 5%. Agreement for all four calculations improves as the resonance energy increases. We have used our experimental and theoretical results to produce Maxwellian-averaged rate coefficients for ΔN = 0 DR of Fe XX. For kBTe ≳ 1 eV, which includes the predicted formation temperatures for Fe XX in an optically thin, low-density photoionized plasma with cosmic abundances, the experimental and theoretical results agree to better than ≈15%. This is within the total estimated experimental uncertainty limits of ≲20%. Agreement below ≈1 eV is difficult to quantify due to current theoretical and experimental limitations. Agreement with previously published LS-coupling rate coefficients is poor, particularly for kBTe ≲ 80 eV. This is attributed to errors in the resonance energies of these calculations as well as the omission of DR via 2p1/2 → 2p3/2 core excitations. We have also used our R-matrix results, topped off using AUTOSTRUCTURE for RR into J ≥ 25 levels, to calculate the rate coefficient for RR of Fe XX. Our RR results are in good agreement with previously published calculations. We find that for temperatures as low as kBTe ≈ 10-3 eV, DR still dominates over RR for this system.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesRate Coefficients for D(1s) + H+ ⇆ D+ + H(1s) Charge Transfer and Some Astrophysical Implications
http://academiccommons.columbia.edu/catalog/ac:158134
Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19457Mon, 25 Mar 2013 00:00:00 +0000We have calculated the rate coefficients for D(1s) + H+ ⇆ D+ + H(1s) using recently published theoretical cross sections. We present results for temperatures T from 1 K up to 2 × 105 K and provide fits to our data for use in plasma modeling. Our calculations are in good agreement with previously published rate coefficients for 25 ≤ T ≤ 300 K, which covers most of the limited range for which those results were given. Our new rate coefficients for T ≳100 K are significantly larger than the values most commonly used for modeling the chemistry of the early universe and of molecular clouds. This may have important implications for the predicted HD abundance in these environments. Using our results, we have modeled the ionization balance in high-redshift QSO absorbers. We find that the new rate coefficients decrease the inferred D/H ratio by ≲0.4%. This is a factor of ≳25 smaller than the current ≳10% uncertainties in QSO absorber D/H measurements.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesLaboratory Measurements of Fe XXIV L-Shell Line Emission
http://academiccommons.columbia.edu/catalog/ac:158137
Savin, Daniel Wolf; Beiersdorfer, P.; Lopez-Urrutia, J. Crespo; Decaux, V.; Gullikson, E. M.; Kahn, S. M.; Liedahl, D. A.; Reed, K. J.; Widmann, K.http://hdl.handle.net/10022/AC:P:19458Mon, 25 Mar 2013 00:00:00 +0000Recent ASCA spectra exhibit discrepancies with the relative line intensities of various Fe XXIII and XXIV L-shell emission lines predicted by standard plasma emission codes. To address this issue, we have carried out a series of high-resolution, broadband measurements of Fe XXIV line emission using an electron beam ion trap facility. X-ray lines produced in the trap are detected and resolved using Bragg crystal spectrometers. We report measurements of 3 → 2 and 4 → 2 transitions, which result primarily from electron impact excitation. Overall, good agreement is found with distorted wave calculations.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesUncertainties in Dielectronic Recombination Rate Coefficients: Effects on Solar and Stellar Upper Atmosphere Abundance Determinations
http://academiccommons.columbia.edu/catalog/ac:158146
Savin, Daniel Wolf; Laming, J. M.http://hdl.handle.net/10022/AC:P:19460Mon, 25 Mar 2013 00:00:00 +0000We have investigated how the relative elemental abundances inferred from the solar upper atmosphere are affected by uncertainties in the dielectronic recombination (DR) rate coefficients used to analyze the spectra. We find that the inferred relative abundances can be up to a factor of ≈5 smaller or ≈1.6 larger than those inferred using the currently recommended DR rate coefficients. We have also found a plausible set of variations to the DR rate coefficients that improve the inferred (and expected) isothermal nature of solar coronal observations at heights of ≳50'' off the solar limb. Our results can be used to help prioritize the enormous amount of DR data needed for modeling solar and stellar upper atmospheres. Based on the work here, our list of needed rate coefficients for DR onto specific isoelectronic sequences reads, in decreasing order of importance, as follows: O-like, C-like, Be-like, N-like, B-like, F-like, Li-like, He-like, and Ne-like. It is our hope that this work will help to motivate and prioritize future experimental and theoretical studies of DR.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesAssessment of the Fluorescence and Auger Database Used in Plasma Modeling
http://academiccommons.columbia.edu/catalog/ac:158131
Savin, Daniel Wolf; Gorczyca, T. W.; Kodituwakku, C. N.; Korista, K. T.; Zatsarinny, O.; Badnell, N. R.; Behar, E.; Chen, M. H.http://hdl.handle.net/10022/AC:P:19452Mon, 25 Mar 2013 00:00:00 +0000We have investigated the accuracy of the 1s vacancy fluorescence database of Kaastra and Mewe resulting from the initial atomic physics calculations and the subsequent scaling along isoelectronic sequences. In particular, we have focused on the relatively simple Be- and F-like 1s vacancy sequences. We find that the earlier atomic physics calculations for the oscillator strengths and autoionization rates of singly charged B II and Ne II are in sufficient agreement with our present calculations. However, the substantial charge dependence of these quantities along each isoelectronic sequence, the incorrect configuration averaging used for B II, and the neglect of spin-orbit effects (which become important at high Z) all cast doubt on the reliability of the Kaastra and Mewe data for application to plasma modeling.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesDielectronic Recombination of Fe XIX Forming Fe XVIII: Laboratory Measurements and Theoretical Calculations
http://academiccommons.columbia.edu/catalog/ac:158173
Savin, Daniel Wolf; Gorczyca, T. W.; Zatsarinny, O.; Badnell, N. R.; Chen, M. H.; Kahn, S. M.; Linkemann, J.; Saghiri, A. A.; Schmitt, M.; Grieser, M.; Repnow, R.; Schwalm, D.; Wolf, A.; Muller, A.; Schippers, S.http://hdl.handle.net/10022/AC:P:19456Mon, 25 Mar 2013 00:00:00 +0000We have measured resonance strengths and energies for dielectronic recombination (DR) of Fe XIX forming Fe XVIII via N = 2 → N' = 2 and N = 2 → N' = 3 core excitations. 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 calculated these resonance strengths and energies using two independent, state-of-the-art techniques: the perturbative multiconfiguration Breit-Pauli (MCBP) and multiconfiguration Dirac-Fock (MCDF) methods. Overall, reasonable agreement is found between our experimental results and theoretical calculations. The most notable discrepancies are for the 3l3l' resonances. The calculated MCBP and MCDF resonance strengths for the n = 3 complex lie, respectively, ≈47% and ≈31% above the measured values. These discrepancies are larger than the estimated ≲ 20% total experimental uncertainty in our measurements. We have used our measured 2 → 2 and 2 → 3 results to produce a Maxwellian-averaged rate coefficient for DR of Fe XIX. Our experimentally derived rate coefficient is estimated to be good to better than ≈20% for kBTe ≥ 1 eV. Fe XIX is predicted to form in photoionized and collisionally ionized cosmic plasmas at kBTe Gt 1 eV. Hence, our rate coefficient is suitable for use in ionization balance calculations of these plasmas. Previously published theoretical DR rate coefficients are in poor agreement with our experimental results. None of these published calculations reliably reproduce the magnitude or temperature dependence of the experimentally derived rate coefficient. Our MCBP and MCDF results agree with our experimental rate coefficient to within ≈20%.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesExperimental M1 Transition Rates of Coronal Lines from Ar X, Ar XIV, and Ar XV
http://academiccommons.columbia.edu/catalog/ac:158179
Savin, Daniel Wolf; Trabert, E.; Beiersdorfer, P.; Utter, S. B.; Brown, G. V.; Chen, H.; Harris, C. L.; Neill, P. A.; Smith, A. J.http://hdl.handle.net/10022/AC:P:19463Mon, 25 Mar 2013 00:00:00 +0000Transition probabilities of three magnetic dipole (M1) transitions in multiply charged ions of Ar have been measured using the Livermore electron-beam ion trap. Two of the transitions are in the ground configurations of Ar XIV (B-like) and Ar IX (F-like), and are associated with the coronal lines at 4412.4 and 5533.4 ÅŽ , respectively. The third is in the excited 2s2p configuration of Be-like Ar XV and produces the coronal line at 5943.73 Å. Our results for the three atomic level lifetimes are 9.32^0.12 ms for the Ar X 2s22p5 2P1/2 level, 9.70^0.15 ms for the Ar XIV 2s22p level, and 15.0^0.8 ms for the Ar XVo 2P3/2o 2s2p level. These results diff†er significantly from earlier measurements and are the most accurate ones to date.Astrophysics, Atomic physicsdws26Astronomy and AstrophysicsArticlesLaboratory Measurements of Iron L-Shell Emission: 3→2 Transitions of Fe XXI-XXIV between 10.5 and 12.5 Å
http://academiccommons.columbia.edu/catalog/ac:158170
Savin, Daniel Wolf; Gu, M. F.; Kahn, S. M.; Behar, E.; Beiersdorfer, P.; Brown, G. V.; Liedahl, D. A.; Reed, K. J.http://hdl.handle.net/10022/AC:P:19461Mon, 25 Mar 2013 00:00:00 +0000Using the electron beam ion trap EBIT-II facility at Lawrence Livermore National Laboratory, we have measured the iron L-shell spectrum between 10.5 and 12.5 Å for Fe XXI-XXIV with a spectral resolution of ~30 mÅ. The relative line intensities of strong 3 → 2 transitions for each charge state are measured as functions of electron energy and compared to distorted wave (DW) calculations. The contributions of resonant processes, namely, resonant excitation (RE) and spectroscopically unresolved dielectronic recombination (DR) satellites, are investigated. The RE contributions are shown to be less than the experimental and theoretical uncertainties for plasma in collisional ionization equilibrium. The unresolved DR satellites, however, enhance the emissivities of almost all lines, some by as large as 15%, consistent with our earlier measurements for Fe XXIV. The DW results agree with our measurements to better than 20% under the condition of collisional ionization equilibrium. The line emissivities in the widely used spectral synthesis model, MEKAL, are also compared to our measurements and are found to be discrepant at a greater than 20% level for some lines.Astrophysics, Atomic physicsdws26Astronomy and AstrophysicsArticlesStorage Ring Cross Section Measurements for Electron Impact Ionization of Fe11+ Forming Fe12+ and Fe13+
http://academiccommons.columbia.edu/catalog/ac:157901
Hahn, Michael; Bernhardt, D.; Grieser, M.; Krantz, C.; Lestinsky, M.; Muller, A.; Novotny, Oldrich; Repnow, R.; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19396Fri, 22 Mar 2013 00:00:00 +0000We report ionization cross section measurements for electron impact single ionization (EISI) of Fe11+ forming Fe12+ and electron impact double ionization (EIDI) of Fe11+ forming Fe13+. The measurements cover the center-of-mass energy range from approximately 230 eV to 2300 eV. The experiment was performed using the heavy-ion storage ring TSR located at the Max-Planck-Institut für Kernphysik in Heidelberg, Germany. The storage ring approach allows nearly all metastable levels to relax to the ground state before data collection begins. We find that the cross section for single ionization is 30% smaller than was previously measured in a single-pass experiment using an ion beam with an unknown metastable fraction. We also find some significant differences between our experimental cross section for single ionization and recent distorted wave (DW) calculations. The DW Maxwellian EISI rate coefficient for Fe11+ forming Fe12+ may be underestimated by as much as 25% at temperatures for which Fe11+ is abundant in collisional ionization equilibrium. This is likely due to the absence of 3s excitation-autoionization (EA) in the calculations. However, a precise measurement of the cross section due to this EA channel was not possible because this process is not distinguishable experimentally from electron impact excitation of an n = 3 electron to levels of n ≥ 44 followed by field ionization in the charge state analyzer after the interaction region. Our experimental results also indicate that the EIDI cross section is dominated by the indirect process in which direct single ionization of an inner shell 2l electron is followed by autoionization, resulting in a net double ionization.Astrophysics, Atomic physics, Plasma physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesProperties of a Polar Coronal Hole During the Solar Minimum in 2007
http://academiccommons.columbia.edu/catalog/ac:157898
Hahn, Michael; Landi, E.; Bryans, P.; Miralles, M. P.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19395Fri, 22 Mar 2013 00:00:00 +0000We report measurements of a polar coronal hole during the recent solar minimum using the Extreme Ultraviolet Imaging Spectrometer on Hinode. Five observations are analyzed that span the polar coronal hole from the central meridian to the boundary with the quiet-Sun corona. We study the observations above the solar limb in the height range of 1.03-1.20 R ☉. The electron temperature T e and emission measure (EM) are found using a geometric mean emission measure method. The EM derived from the elements Fe, Si, S, and Al are compared in order to measure relative coronal-to-photospheric abundance enhancement factors. We also studied the ion temperature T i and the non-thermal velocity v nt using the line profiles. All these measurements are compared to polar coronal hole observations from the previous (1996-1997) solar minimum and to model predictions for relative abundances. There are many similarities in the physical properties of the polar coronal holes between the two minima at these low heights. We find that the electron density, T e, and T i are comparable in both minima. T e shows a comparable gradient with height. Both minima show a decreasing T i with increasing charge-to-mass ratio q/M. A previously observed upturn of T i for ions above q/M>0.25 was not found here. We also compared relative coronal-to-photospheric elemental abundance enhancement factors for a number of elements. These ratios were ~1 for both the low first ionization potential (FIP) elements Si and Al and the marginally high FIP element S relative to the low FIP element Fe, as is expected based on earlier observations and models for a polar coronal hole. These results are consistent with no FIP effect in a polar coronal hole.Astrophysics, Atomic physicsmh2451, dws26Astronomy and AstrophysicsArticlesEffects of Configuration Interaction for Dielectronic Recombination of Na-like Ions Forming Mg-like Ions
http://academiccommons.columbia.edu/catalog/ac:157904
Kwon, D. H.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19397Fri, 22 Mar 2013 00:00:00 +0000Theoretical dielectronic recombination (DR) rate coefficient calculations can be sensitive to configuration interaction (CI) between resonances with different captured electron principle quantum numbers n. Here we explore the importance of this multi-n CI process for DR via 2l → 3l' core excitations and its effect on the total DR rate coefficient. Results are presented for selected Na-like ions from Ca9 + to Zn19 +. We find that including this multi-n CI can reduce the DR rate coefficient by up to ~10% at temperatures where an ion is predicted to form in collisional ionization equilibrium and up to ~15% at higher temperatures. To a first approximation, this will translate into a corresponding increase in the ion abundance. Charge state distributions calculation seeking to be accurate to better than 10% will thus need to take this effect into account. We also present simple fits to the calculated rate coefficients for ease of incorporation into plasma models.Astrophysics, Atomic physics, Plasma physicsdws26Astronomy and AstrophysicsArticlesTheoretical electron-impact-ionization cross section for Fe11+ forming Fe12+
http://academiccommons.columbia.edu/catalog/ac:158077
Kwon, D. H.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19418Fri, 22 Mar 2013 00:00:00 +0000We have calculated cross sections for electron impact ionization (EII) of P-like Fe11+ forming Si-like Fe12+. We have used the flexible atomic code (FAC) and a distorted-wave (DW) approximation. Particular attention has been paid to the ionization through the 3l→nl′ and 2l→nl′ excitation autoionization (EA) channels. We compare our results to previously published FAC DW results and recent experimental results. We find that the previous discrepancy between theory and experiment at the EII threshold can be accounted for by the 3l→nl′ EA channels which were not included in the earlier calculations. At higher energies the discrepancy previously seen between theory and experiment for the magnitude of the 2l→nl′ (n≥4) EA remains, though the difference has been reduced by our newer results. The resulting Maxwellian rate coefficient derived from our calculations lies within 11% of the experimentally derived rate coefficient in the temperature range where Fe11+ forms in collisional ionization equilibrium.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesAssociative detachment of H− + H → H2 + e−
http://academiccommons.columbia.edu/catalog/ac:158068
Savin, Daniel Wolf; Bruhns, H.; Kreckel, H.; Miller, Kenneth; Urbain, X.; Eliasek, J.; Cizek, M.http://hdl.handle.net/10022/AC:P:19415Fri, 22 Mar 2013 00:00:00 +0000Using a merged-beams apparatus, we have measured the associative detachment (AD) reaction of H−+H→H2+e− for relative collision energies up to Er≤4.83 eV. These data extend above the 1-eV limit of our earlier results. We have also updated our previous theoretical work to account for AD via the repulsive 2Σg+ H2− potential energy surface and for the effects at Er≥0.76 eV on the experimental results due to the formation of long-lived H2 resonances lying above the H+H separated atoms limit. Merging both experimental data sets, our results are in good agreement with our new theoretical calculations and confirm the prediction that this reaction essentially turns off for Er≳2 eV. Similar behavior has been predicted for the formation of protonium from collisions of antiprotons and hydrogen atoms.Astrophysics, Atomic physicsdws26, kam2211Astronomy and AstrophysicsArticlesElectron-impact-ionization measurements using hyperfine-assisted state preparation of ground-state berylliumlike sulfur
http://academiccommons.columbia.edu/catalog/ac:158074
Lestinsky, M.; Bernhardt, D.; Grieser, M.; Hahn, Michael; Krantz, C.; Novotny, Oldrich; Repnow, R.; Muller, A.; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19417Fri, 22 Mar 2013 00:00:00 +0000We have measured electron impact ionization (EII) of the beryllium-like ion S12+. The use of an isotopically pure A=33 beam of S12+ ions is established as a method to eliminate all metastable levels, including the extremely long-lived metastable level 2s2p 3 P0, which, for this isotope, decays by hyperfine-induced radiative transitions. The energy dependence and absolute size of the EII cross section were measured from the resulting pure ground-state population at energies from below the threshold at ≈ 652.2 eV up to 3000 eV. These data provide an experimental benchmark for theory.Astrophysics, Atomic physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesIsotope effect for associative detachment: H(D)−+H(D)→H2(D2)+e
http://academiccommons.columbia.edu/catalog/ac:158080
Savin, Daniel Wolf; Bruhns, H.; Kreckel, H.; Miller, Kenneth; Urbain, X.; Eliasek, J.; Cizek, M.; Cabrera-Trujillo, R.; O'Connor, Aodhhttp://hdl.handle.net/10022/AC:P:19419Fri, 22 Mar 2013 00:00:00 +0000We report experimental and theoretical results for associative detachment (AD) of D−+D→D2+e−. We compare these data to our previously published results for H−+H→H2+e−. The measurements show no significant isotope effect in the total cross section. This is to be contrasted with previously published experimental and theoretical work which has found a significant isotope effect in diatomic systems for partial AD cross sections, i.e., as a function of the rotational and vibrational levels of the final molecule formed. Our work implies that though the rovibrational distribution of flux is different for AD of H− + H and D− + D, the total flux for these two systems is essentially the same when summed over all possible final channels.Astrophysics, Atomic physicsdws26, kam2211, apo2117Astronomy and AstrophysicsArticlesCollisional Ionization Equilibrium for Optically Thin Plasmas. I. Updated Recombination Rate Coefficients for Bare through Sodium-like Ions
http://academiccommons.columbia.edu/catalog/ac:158086
Savin, Daniel Wolf; Bryans, P.; Badnell, N. R.; Gorczyca, T. W.; Laming, J. M.; Mitthumsiri, W.http://hdl.handle.net/10022/AC:P:19423Fri, 22 Mar 2013 00:00:00 +0000Reliably interpreting spectra from electron-ionized cosmic plasmas requires accurate ionization balance calculations for the plasma in question. However, much of the atomic data needed for these calculations have not been generated using modern theoretical methods and are often highly suspect. This translates directly into the reliability of the collisional ionization equilibrium (CIE) calculations. We make use of state-of-the-art calculations of dielectronic recombination (DR) rate coefficients for the hydrogenic through Na-like ions of all elements from He up to and including Zn. Where measurements exist, these published theoretical DR data agree with recent laboratory work to within typically 35% or better at the temperatures relevant for CIE. We also make use of state-of-the-art radiative recombination (RR) rate coefficient calculations for the bare through Na-like ions of all elements from H through to Zn. Here we present improved CIE calculations for temperatures from 104 to 109 K using our data and the recommended electron impact ionization data of Mazzotta et al. for elements up to and including Ni and Mazzotta for Cu and Zn. DR and RR data for ionization stages that have not been updated are also taken from these two additional sources. We compare our calculated fractional ionic abundances using these data with those presented by Mazzotta et al. for all elements from H to Ni. The differences in peak fractional abundance are up to 60%. We also compare with the fractional ionic abundances for Mg, Si, S, Ar, Ca, Fe, and Ni derived from the modern DR calculations of Gu for the H-like through Na-like ions, and the RR calculations of Gu for the bare through F-like ions. These results are in better agreement with our work, with differences in peak fractional abundance of less than 10%.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesMeasurement and interpretation of the polarization of the x-ray line emission of heliumlike Fe XXV excited by an electron beam
http://academiccommons.columbia.edu/catalog/ac:158083
Savin, Daniel Wolf; Beiersdorfer, P.; Vogel, D. A.; Reed, K. J.; Decaux, V.; Scofield, J. H.; Widmann, K.; Holzer, G.; Forster, E.; Wehrhan, O.; Schweikhard, L.http://hdl.handle.net/10022/AC:P:19420Fri, 22 Mar 2013 00:00:00 +0000The linear polarization of the 1s2p 1P1→1s2 1S0 resonance line, the 1s2p 3P1,2→1s2 1S0 intercombination lines, and the 1s2s 3S1→1s2 1S0 forbidden line was measured in heliumlike Fe XXV excited near threshold by a monoenergetic electron beam. The measurement was carried out with a high-resolution x-ray spectrometer employing a set of two analyzing crystals that acted as polarizers by selectively reflecting the individual polarization components. A value of +0.56-0.08+0.17 was determined for the polarization of the 1P1 line, -0.53-0.02+0.05 for the 3P2 line, -0.22-0.02+0.05 for the 3P1 line, and -0.076-0.007+0.007 for the 3S1 line. The measurements were compared with results from a relativistic distorted-wave calculation, which was carried out for a number of mid-Z heliumlike ions (Mg10+–Kr34+), and good agreement was found. By contrast, disagreement was noted with predictions based on Coulomb-Born calculations, allowing us to distinguish between theoretical approaches.Astrophysics, Atomic physicsdws26Astronomy and AstrophysicsArticlesStorage-ring measurement of the hyperfine-induced 2s2p 3 P0→2s2 1 S0 transition rate in berylliumlike sulfur
http://academiccommons.columbia.edu/catalog/ac:158071
Lestinsky, M.; Bernhardt, D.; Grieser, M.; Hahn, Michael; Krantz, C.; Novotny, Oldrich; Repnow, R.; Muller, A.; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19416Fri, 22 Mar 2013 00:00:00 +0000The hyperfine-induced 2s 2p 3 P0→2s2 1 S0 transition rate in Be-like sulfur was measured by monitoring the decay of isotopically pure beams of 32S12+ and 33S12+ ions in a heavy-ion storage ring. Within the 4% experimental uncertainty the experimental value of 0.096(4) s−1 agrees with the most recent theoretical results of [ Cheng et al. Phys. Rev. A 77 052504 (2008)] and [ Andersson et al. Phys. Rev. A 79 032501 (2009)]. Repeated experiments with different magnetic fields in the storage-ring bending magnets demonstrate that artificial quenching of the 2s 2p 3 P0 state by these magnetic fields is negligible.Astrophysics, Plasma physics, Atomic physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesDielectronic recombination of xenonlike tungsten ions
http://academiccommons.columbia.edu/catalog/ac:158065
Lestinsky, M.; Bernhardt, D.; Grieser, M.; Hahn, Michael; Krantz, C.; Novotny, Oldrich; Repnow, R.; Muller, A.; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19414Fri, 22 Mar 2013 00:00:00 +0000Dielectronic recombination (DR) of xenonlike W20+ forming W19+ has been studied experimentally at a heavy-ion storage ring. A merged-beams method has been employed for obtaining absolute rate coefficients for electron-ion recombination in the collision-energy range 0–140 eV. The measured rate coefficient is dominated by strong DR resonances even at the lowest experimental energies. At plasma temperatures where the fractional abundance of W20+ is expected to peak in a fusion plasma, the experimentally derived plasma recombination rate coefficient is over a factor of 4 larger than the theoretically calculated rate coefficient which is currently used in fusion plasma modeling. The largest part of this discrepancy stems most probably from the neglect in the theoretical calculations of DR associated with fine-structure excitations of the W20+([Kr]4d10 4f8) ion core.Astrophysics, Plasma physics, Atomic physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesMeasurements of Anisotropic Ion Temperatures, Non-Thermal Velocities, and Doppler Shifts in a Coronal Hole
http://academiccommons.columbia.edu/catalog/ac:158038
Hahn, Michael; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19405Fri, 22 Mar 2013 00:00:00 +0000We present a new diagnostic allowing one to measure the anisotropy of ion temperatures and non-thermal velocities, as well as Doppler shifts with respect to the ambient magnetic field. This method provides new results, as well as an independent test for previous measurements obtained with other techniques. Our spectral data come from observations of a low-latitude, on-disk coronal hole. A potential field source surface model was used to calculate the angle between the magnetic field lines and the line of sight for each spatial bin of the observation. A fit was performed to determine the line widths and Doppler shifts parallel and perpendicular to the magnetic field. For each line width component we derived ion temperatures T i, ⊥ and T i, ∥ and non-thermal velocities v nt, ⊥ and v nt, ∥. T i, ⊥ was cooler than off-limb polar coronal hole measurements, suggesting increasing collisional cooling with decreasing height. T i, ∥ is consistent with a uniform temperature of (1.8 ± 0.2) × 106 K for each ion. Since parallel ion heating is expected to be weak, this ion temperature should reflect the proton temperature. A comparison between our results and others implies a large proton temperature gradient around 1.02 R ☉. The non-thermal velocities are thought to be proportional to the amplitudes of various waves. Our results for v nt, ⊥ agree with Alfvén wave amplitudes inferred from off-limb polar coronal hole line width measurements. Our v nt, ∥ results are consistent with slow magnetosonic wave amplitudes inferred from Fourier analysis of time-varying intensity fluctuations. Doppler shift measurements yield outflows of ≈5 km s–1 for ions formed over a broad temperature range. This differs from other studies that found a strong Doppler shift dependence on formation temperature.Astrophysics, Plasma physics, Atomic physicsmh2451, dws26Astronomy and AstrophysicsArticlesIs H+3 cooling ever important in primordial gas?
http://academiccommons.columbia.edu/catalog/ac:158044
Glover, S. C. O.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19407Fri, 22 Mar 2013 00:00:00 +0000Studies of the formation of metal-free Population III stars usually focus primarily on the role played by H2 cooling, on account of its large chemical abundance relative to other possible molecular or ionic coolants. However, while H2 is generally the most important coolant at low gas densities, it is not an effective coolant at high gas densities, owing to the low critical density at which it reaches local thermodynamic equilibrium (LTE) and to the large opacities that develop in its emission lines. It is therefore possible that emission from other chemical species may play an important role in cooling high-density primordial gas. A particularly interesting candidate is the H+3 molecular ion. This ion has an LTE cooling rate that is roughly a billion times larger than that of H2, and unlike other primordial molecular ions such as H +2 or HeH+, it is not easily removed from the gas by collisions with H or H2. It is already known to be an important coolant in at least one astrophysical context – the upper atmospheres of gas giants – but its role in the cooling of primordial gas has received little previous study. In this paper, we investigate the potential importance of H+3 cooling in primordial gas using a newly developed H+3 cooling function and the most detailed model of primordial chemistry published to date. We show that although H+3 is, in most circumstances, the third most important coolant in dense primordial gas (after H2 and HD), it is nevertheless unimportant, as it contributes no more than a few per cent of the total cooling. We also show that in gas irradiated by a sufficiently strong flux of cosmic rays or X-rays, H+3 can become the dominant coolant in the gas, although the size of the flux required renders this scenario unlikely to occur.Astrophysics, Atomic physicsdws26Astronomy and AstrophysicsArticlesElectron–Ion Recombination of Fe XII Forming Fe XI: Laboratory Measurements and Theoretical Calculations
http://academiccommons.columbia.edu/catalog/ac:158050
Lestinsky, M.; Badnell, N. R.; Bernhardt, D.; Grieser, M.; Hahn, Michael; Krantz, C.; Novotny, Oldrich; Repnow, R.; Muller, A.; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19409Fri, 22 Mar 2013 00:00:00 +0000We have measured electron–ion recombination for Fe xii forming Fe xi using a merged-beam configuration at the heavy-ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. The measured merged-beam recombination rate coefficient (MBRRC) for collision energies from 0 to 1500 eV is presented. This work uses a new method for determining the absolute MBRRC based on a comparison of the ion beam decay rate with and without the electron beam on. For energies below 75 eV, the spectrum is dominated by dielectronic recombination (DR) resonances associated with 3s → 3p and 3p → 3d core excitations. At higher energies, we observe contributions from 3 → N' and 2 → N' core excitation DR. We compare our experimental results to state-of-the-art multi-configuration Breit-Pauli (MCBP) calculations and find significant differences, both in resonance energies and strengths. We have extracted the DR contributions from the measured MBRRC data and transformed them into a plasma recombination rate coefficient (PRRC) for temperatures in the range of 103–107 K. We show that the previously recommended DR data for Fe xii significantly underestimate the PRRC at temperatures relevant for both photoionized plasmas (PPs) and collisionally ionized plasmas (CPs). This is contrasted with our MCBP PRRC results, which agree with the experiment to within 30% at PP temperatures and even better at CP temperatures. We find this agreement despite the disagreement shown by the detailed comparison between our MCBP and experimental MBRRC results. Last, we present a simple parameterized form of the experimentally derived PRRC for easy use in astrophysical modeling codes.Astrophysics, Plasma physics, Atomic physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesAbsolute-rate coefficient for C3+(2s→2p) electron-impact excitation
http://academiccommons.columbia.edu/catalog/ac:158053
Gardner, L. D.; Reisenfeld, D. B.; Young, A. R.; Kohl, J. L.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19410Fri, 22 Mar 2013 00:00:00 +0000We have measured the absolute-rate coefficient for electron-impact excitation (EIE) of C3+(2s 2S1/2→2p 2P1/2,3/2) for energies near threshold. A delayed coincidence technique with inclined beams was used. Radiation from the excited ions was detected using an optical system that subtends slightly over π steradians. At an ion-rest-frame energy of 10.10 eV the measured rate coefficient was (7.79±2.10)×10-8 cm3 s-1 and the measured cross section was (4.15±1.12)×10-16 cm2. The uncertainties quoted here represent the total experimental uncertainty, statistical and systematic, at a confidence level considered to be equivalent to a statistical 90% confidence level. Good agreement is found with other measurements. Agreement is not good with Coulomb-Born with exchange and two-state close-coupling calculations, both of which fall outside our 90% confidence limits. Nine-state close-coupling calculations are in better agreement. However, the calculations lie at the extreme edge of our uncertainty limits. Taking into account previous measurements of EIE in C3+ and also a measurement of EIE in Li-like Be+ that falls significantly below theory at threshold, there is a suggestion that the C3+(2s→2p) EIE rate coefficient near threshold may fall slightly below presently accepted values.Astrophysics, Atomic physicsdws26Astronomy and AstrophysicsArticlesAbsolute measurement of dielectronic recombination for C3+ in a known external field
http://academiccommons.columbia.edu/catalog/ac:158056
Savin, Daniel Wolf; Kohl, J. L.; Young, A. R.; Gardner, L. D.; Reisenfeld, D. B.http://hdl.handle.net/10022/AC:P:19411Fri, 22 Mar 2013 00:00:00 +0000An absolute measurement of the rate coefficient for dielectronic recombination (DR) of C3+, via the 2s-2p core excitation, in an external electric field of 11.4±0.9(1σ) V cm-1 is presented. An inclined-beam arrangement is used and the stabilizing photons at ∼155 nm are detected in delayed coincidence with the recombined ions. The full width at half maximum of the electron energy spread in the ion rest frame is 1.74±0.22(1σ) eV. The measured DR rate, at a mean electron energy of 8.26±0.07(1σ) eV, is (2.76±0.75)×10-10 cm3 s-1. The uncertainty quoted for the DR rate is the total uncertainty, systematic and statistical, at the 1σ level. In comparing the present results to theory, a semiempirical formula is used to determine which recombined ion states are ionized by the 4.65 kV cm-1 fields in the final-charge-state analyzer and not detected. For the present results, any DR of the incident electrons into n levels greater than 44 is assumed to be field ionized in the final-charge-state analyzer. A more precise treatment of field ionization, which includes the lifetime of the C2+ ions before they are ionized and the time evolution and rotation of the fields experienced by the recombined ions, is needed before a definitive comparison between experiment and theory can be made. Our DR measurement, within the limits of that approach, agrees reasonably well with an intermediate coupling calculation that uses an isolated resonance, single-configuration approximation, but does not agree with pure LS-coupling calculations.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesElectron-Ion Recombination of Mg6 + Forming Mg5 + and Of Mg7 + Forming Mg6 +: Laboratory Measurements and Theoretical Calculations
http://academiccommons.columbia.edu/catalog/ac:158041
Lestinsky, M.; Badnell, N. R.; Bernhardt, D.; Grieser, M.; Bing, D.; Hahn, Michael; Hoffman, J.; Jordon-Thaden, B.; Krantz, C.; Novotny, Oldrich; Orlov, D. A.; Repnow, R.; Shornikov, A.; Muller, A.; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19406Fri, 22 Mar 2013 00:00:00 +0000We have measured electron-ion recombination for C-like Mg6 + forming Mg5 +, and for B-like Mg7 + forming Mg6 +. These studies were performed using a merged electron-ion beam arrangement at the TSR heavy ion storage ring located in Heidelberg, Germany. Both primary ions have metastable levels with significant lifetimes. Using a simple cascade model we estimate the population fractions in these metastable levels. For the Mg6 + results, we find that the majority of the stored ions are in a metastable level, while for Mg7 + the metastable fraction is insignificant. We present the Mg6 + merged beams recombination rate coefficient for DR via N = 2 → N' = 2 core electron excitations (ΔN = 0 DR) and for Mg7 + via 2 → 2 and 2 → 3 core excitations. Taking the estimated metastable populations into account, we compare our results to state-of-the-art multiconfiguration Breit-Pauli theoretical calculations. Significant differences are found at low energies where theory is known to be unreliable. Moreover, for both ions we observe a discrepancy between experiment and theory for ΔN = 0 DR involving capture into high-n Rydberg levels and where the stabilization is primarily due to a radiative transition of the excited core electron. This is consistent with previous DR experiments on M-shell iron ions which were performed at TSR. The large metastable content of the Mg6 + ion beam precludes generating a plasma recombination rate coefficient (PRRC). However, this is not an issue for Mg7 + and we present an experimentally derived Mg7 + PRRC for plasma temperatures from 400 K to 107 K with an estimated uncertainty of less than 27% at a 90% confidence level. We also provide a fit to our experimentally derived PRRC for use in plasma modeling codes.Astrophysics, Plasma physics, Atomic physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesAbsolute energy-resolved measurements of the H-+H→H2+e- associative detachment reaction using a merged-beam apparatus
http://academiccommons.columbia.edu/catalog/ac:158062
Savin, Daniel Wolf; Bruhns, H.; Kreckel, H.; Miller, Kenneth; Urbain, X.http://hdl.handle.net/10022/AC:P:19413Fri, 22 Mar 2013 00:00:00 +0000Using a merged-beam configuration, we have performed absolute measurements for the associative detachment reaction H-+H→H2+e-. Our energy-resolved measurements for this process remove a long-standing discrepancy between theory and experiment for this fundamental reaction. In particular, we find excellent agreement with theoretical results which previously seemed to be ruled out by earlier experiments performed using a flowing afterglow technique.Astrophysics, Atomic physicsdws26, kam2211Astronomy and AstrophysicsArticlesIs H+3 cooling ever important in primordial gas?
http://academiccommons.columbia.edu/catalog/ac:158047
Glover, S. C. O.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19408Fri, 22 Mar 2013 00:00:00 +0000Full tables of " Is H+3 cooling ever important in primordial gas?".Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsDatasetsStorage Ring Cross-Section Measurements for Electron Impact Single and Double Ionization of Fe9 + and Single Ionization of Fe10 +
http://academiccommons.columbia.edu/catalog/ac:158026
Hahn, Michael; Becker, A.; Grieser, M.; Krantz, C.; Lestinsky, M.; Muller, A.; Novotny, Oldrich; Repnow, R.; Schippers, S.; Spruck, K.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19401Fri, 22 Mar 2013 00:00:00 +0000We have measured electron impact ionization from the ground state of Fe9 + and Fe10 + over the relative electron-ion collision energy ranges 200-1900 eV and 250-1800 eV, respectively. The ions were confined in an ion storage ring long enough for essentially all metastable levels to radiatively relax to the ground state. For single ionization, we find a number of discrepancies between the existing theoretical cross sections and our results. The calculations appear to neglect some excitation-autoionization (EA) channels, particularly from n = 3 to n' excitations, which are important near threshold, and those from n = 2 → 3 excitations, which contribute at about 650 eV. Conversely, at higher energies the calculations appear to overestimate the importance of EA channels due to excitation into levels where n ≥ 4. The resulting experimental rate coefficients agree with the most recent theory for Fe9 + to within 16% and for Fe10 + to within 19% at temperatures where these ions are predicted to form in collisional ionization equilibrium. We have also measured double ionization of Fe9 + forming Fe11 + in the energy range 450-3000 eV and found that although there is an appreciable cross section for direct double ionization, the dominant mechanism appears to be through direct ionization of an inner shell electron producing an excited state that subsequently stabilizes through autoionization.Astrophysics, Plasma physics, Atomic physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesAddendum: “Storage Ring Measurement of Electron Impact Ionization for Mg7+ Forming Mg8+” (2010, Apj, 712, 1166)
http://academiccommons.columbia.edu/catalog/ac:158029
Hahn, Michael; Bernhardt, D.; Lestinsky, M.; Muller, A.; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19402Fri, 22 Mar 2013 00:00:00 +0000Experimental cross-section data are presented as online data tables for electron impact single ionization of Mg7+ forming Mg8+.Astrophysics, Plasma physics, Atomic physicsmh2451, dws26Astronomy and AstrophysicsArticlesAddendum: “Storage Ring Cross Section Measurements for Electron Impact Ionization of Fe11+ Forming Fe12+ and Fe13+” (2011, Apj, 729, 76)
http://academiccommons.columbia.edu/catalog/ac:158032
Hahn, Michael; Bernhardt, D.; Grieser, M.; Krantz, C.; Lestinsky, M.; Muller, A.; Novotny, Oldrich; Repnow, R.; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19403Fri, 22 Mar 2013 00:00:00 +0000Experimental cross section data are presented as online data tables for electron impact single ionization of Fe11+ forming Fe12+ and electron impact double ionization of Fe11+ forming Fe13+.Astrophysics, Plasma physics, Atomic physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesAddendum: “Storage Ring Cross-Section Measurements for Electron Impact Ionization of Fe12+ Forming Fe13+ and Fe14+” (2011, Apj, 735, 105)
http://academiccommons.columbia.edu/catalog/ac:158035
Hahn, Michael; Grieser, M.; Krantz, C.; Lestinsky, M.; Muller, A.; Novotny, Oldrich; Repnow, R.; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19404Fri, 22 Mar 2013 00:00:00 +0000Experimental cross-section data are presented as online data tables for electron impact single ionization of Fe12+ forming Fe13+ and electron impact double ionization of Fe12+ forming Fe14+.Astrophysics, Plasma physics, Atomic physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesMeasurement of C3+ dielectronic recombination in a known external field
http://academiccommons.columbia.edu/catalog/ac:158059
Savin, Daniel Wolf; Kohl, J. L.; Young, A. R.; Gardner, L. D.; Lafyatis, G. P.; Chutjian, A. ; Bliman, S.http://hdl.handle.net/10022/AC:P:19412Fri, 22 Mar 2013 00:00:00 +0000An experiment to measure the dielectronic recombination of C3+ in a known external electric field is described. The measured value differs from results of calculations which do not include the effects of field enhancement, and is larger than but marginally in agreement with predictions of theoretical methods that include the effects of the external field.Astrophysics, Atomic physicsdws26Astronomy and AstrophysicsArticlesStorage Ring Cross Section Measurements for Electron Impact Ionization of Fe12 + Forming Fe13 + and Fe14 +
http://academiccommons.columbia.edu/catalog/ac:158017
Hahn, Michael; Grieser, M.; Krantz, C.; Lestinsky, M.; Muller, A.; Novotny, Oldrich; Repnow, R.; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19398Fri, 22 Mar 2013 00:00:00 +0000We report electron impact ionization cross section measurements for electron impact single ionization of Fe12 + forming Fe13 + and electron impact double ionization of Fe12 + forming Fe14 +. These are the first electron impact ionization data for any Si-like ion uncontaminated by an unknown metastable fraction. Recent distorted wave calculations agree with our single ionization results to within ~15%. Double ionization is dominated by inner shell ionization of a 2l electron resulting in autoionization of a second electron as the inner shell hole is filled.Astrophysics, Atomic physics, Plasma physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesElectron-Ion Recombination of Fe X Forming Fe IX And of Fe XI Forming Fe X: Laboratory Measurements and Theoretical Calculations
http://academiccommons.columbia.edu/catalog/ac:157847
Lestinsky, M.; Badnell, N. R.; Bernhardt, D.; Grieser, M.; Hoffmann, J.; Lukic, D.; Muller, A.; Orlov, D. A.; Repnow, R.; Savin, Daniel Wolf; Schmidt, E. W.; Schnell, M.; Schippers, S.; Wolf, A.; Yu, D.http://hdl.handle.net/10022/AC:P:19384Wed, 20 Mar 2013 00:00:00 +0000We have measured electron-ion recombination for Fe9+ forming Fe8+ and for Fe10+ forming Fe9+ using a merged beams arrangement at the TSR heavy-ion storage ring in Heidelberg, Germany. The measured merged beams recombination rate coefficients (MBRRC) for relative energies from 0 to 75 eV are presented, covering all dielectronic recombination (DR) resonances associated with 3s → 3p and 3p → 3d core transitions in the spectroscopic species Fe X and Fe XI, respectively. We compare our experimental results to state-of-the-art multiconfiguration Breit-Pauli (MCBP) calculations and find significant differences. Poor agreement between the measured and theoretical resonance structure is seen for collision energies below 48 eV for Fe X and below 35 eV for Fe XI. The integrated resonance strengths, though, are in reasonable agreement. At higher energies, good agreement is seen for the resonance structure but for the resonance strengths theory is significantly larger than experiment by a factor of ≈ 1.5 (2) for Fe X (Fe XI). From the measured MBRRC, we have extracted the DR contributions and transform them into plasma recombination rate coefficients (PRRCs) for astrophysical plasmas with temperatures in the range of 102-107 K. This range spans across the regimes where each ion forms in photoionized or in collisionally ionized plasmas. For both temperature regimes, the experimental uncertainties are 25% at a 90% confidence level. As expected based on predictions from active galactic nucleus observations as well as our previous laboratory and theoretical work on M-shell iron, the formerly recommended DR data severely underestimated the rate coefficient at temperatures relevant for photoionized gas. At these temperatures relevant for photoionized gas, we find agreement between our experimental results and MCBP theory. This is somewhat surprising given the poor agreement in MBRRC resonance structure. At the higher temperatures relevant for collisionally ionized gas, the MCBP calculations yield an Fe XI DR rate coefficient that is significantly larger than the experimentally derived one. We present parameterized fits to our experimentally derived DR PRRC for ease of inclusion into astrophysical modeling codes.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesDielectronic recombination data for dynamic finite-density plasmas II. The oxygen isoelectronic sequence
http://academiccommons.columbia.edu/catalog/ac:157835
Zatsarinny, O.; Gorczyca, T. W.; Korista, K. T.; Fu, J. ; Badnell, N. R.; Mitthumsiri, W.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19380Wed, 20 Mar 2013 00:00:00 +0000Mistakes in an earlier publication (Zatsarinny et al. 2003) have been discovered and are corrected below (in boldface). The first is a missing exponent in an equation, the second is some wrong fitting coefficients for several ions, the third and fourth are an incorrect caption and an incorrect label in a figure, and the fifth is an inaccuracy in high-temperature radiative recombination rate coefficients.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesDielectronic recombination data for dynamic finite-density plasmas II. The oxygen isoelectronic sequence
http://academiccommons.columbia.edu/catalog/ac:157838
Zatsarinny, O.; Gorczyca, T. W.; Korista, K. T.; Badnell, N. R.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19381Wed, 20 Mar 2013 00:00:00 +0000Dielectronic recombination (DR) and radiative recombination (RR) data for oxygen-like ions forming fluorine-like ions have been calculated as part of the assembly of a level-resolved DR and RR database necessary for modelling of dynamic finite-density plasmas (Badnell et al. 2003). Total DR and RR rate coefficients for F+ to Zn22+ are presented and the results discussed. By comparison between perturbative and R-matrix results, we find that RR/DR interference effects are negligible even for the lowest-charged F+ member. We also find that the 2→2 low-temperature DR (no change in the principal quantum number of the core electrons) does not scale smoothly with nuclear charge Z due to resonances straddling the ionization limit, thereby making explicit calculations for each ion necessary. These RR and DR data are suitable for modelling of solar and cosmic plasmas under conditions of collisional ionization equilibrium, photoionization equilibrium, and non-equilibrium ionization.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesStorage Ring Measurement of Electron Impact Ionization for Mg7+ Forming Mg8+
http://academiccommons.columbia.edu/catalog/ac:157850
Hahn, Michael; Bernhardt, D.; Lestinsky, M.; Muller, A.; Novotny, Oldrich; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19385Wed, 20 Mar 2013 00:00:00 +0000We report electron impact ionization cross section measurements for Mg7+ forming Mg8+ at center of mass energies from approximately 200 eV to 2000 eV. The experimental work was performed using the heavy-ion storage ring TSR located at the Max-Planck-Institut für Kernphysik in Heidelberg, Germany. We find good agreement with distorted wave calculations using both the GIPPER code of the Los Alamos Atomic Physics Code suite and using the Flexible Atomic Code.Astrophysics, Atomic physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesElectron-ion recombination for Fe VIII forming Fe VII and Fe IX forming Fe VIII: measurements and theory
http://academiccommons.columbia.edu/catalog/ac:157826
Schmidt, E. W.; Schippers, S.; Bernhardt, D.; Muller, A.; Hoffmann, J.; Orlov, D. A.; Lestinsky, M.; Lukic, D. V.; Wolf, A.; Savin, Daniel Wolf; Badnell, N. R.http://hdl.handle.net/10022/AC:P:19379Wed, 20 Mar 2013 00:00:00 +0000The photorecombination rate coefficients of potassium-like Fe VIII ions forming calcium-like Fe VII and of argon-like Fe IX forming potassium-like Fe VIII were measured by employing the merged electron-ion beams method at the Heidelberg heavy-ion storage-ring TSR. New theoretical calculations with the AUTOSTRUCTURE code were carried out for dielectronic recombination (DR) and trielectronic recombination (TR) for both ions. We compare these experimental and theoretical results and also compare with previously recommended rate coefficients. The DR and TR resonances were experimentally investigated in the electron-ion collision energy ranges 0-120 eV and 0-151 eV for Fe VIII and Fe IX. Experimentally derived Fe VIII and Fe IX DR + TR plasma rate coefficients are provided in the temperature range kBT=0.2 to 1000eV. Their uncertainties amount to ±26% and ±35% at a 90% confidence level for Fe VIII and Fe IX, respectively.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesMolecular Cloud Chemistry and The Importance of Dielectronic Recombination
http://academiccommons.columbia.edu/catalog/ac:157844
Bryans, P.; Kreckel, H.; Roueff, E.; Wakelam, V.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19383Wed, 20 Mar 2013 00:00:00 +0000Dielectronic recombination (DR) of singly charged ions is a reaction pathway that is commonly neglected in chemical models of molecular clouds. In this study we include state-of-the-art DR data for He+, C+, N+, O+, Na+, and Mg+ in chemical models used to simulate dense molecular clouds, protostars, and diffuse molecular clouds. We also update the radiative recombination (RR) rate coefficients for H+, He+, C+, N+, O+, Na+, and Mg+ to the current state-of-the-art values. The new RR data have little effect on the models. However, the inclusion of DR results in significant differences in gas-grain models of dense, cold molecular clouds for the evolution of a number of surface and gas-phase species. We find differences of a factor of 2 in the abundance for 74 of the 655 species at times of 104-106 yr in this model when we include DR. Of these 74 species, 16 have at least a factor of 10 difference in abundance. We find the largest differences for species formed on the surface of dust grains. These differences are due primarily to the addition of C+ DR, which increases the neutral C abundance, thereby enhancing the accretion of C onto dust. These results may be important for the warm-up phase of molecular clouds when surface species are desorbed into the gas phase. We also note that no reliable state-of-the-art RR or DR data exist for Si+, P+, S+, Cl+, and Fe+. Modern calculations for these ions are needed to better constrain molecular cloud models.Astrophysics, Atomic physicsdws26Astronomy and AstrophysicsArticlesDielectronic recombination data for dynamic finite-density plasmas VII. The neon isoelectronic sequence
http://academiccommons.columbia.edu/catalog/ac:157817
Savin, Daniel Wolf; Zatsarinny, O.; Gorczyca, T. W.; Korista, K. T.; Badnell, N. R.http://hdl.handle.net/10022/AC:P:19378Wed, 20 Mar 2013 00:00:00 +0000Dielectronic recombination (DR) and radiative recombination (RR) data for neon-like ions forming sodium-like systems has been calculated as part of the assembly of a DR database necessary for modelling of dynamic and/or finite-density plasmas (Badnell et al. 2003). Dielectronic recombination coefficients for neon-like ions from Na+ to Zn20+, as well as Kr26+, Mo32+, Cd38+, and Xe44+, are presented and the results discussed.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesElectron-Impact Ionization of Be-like C III, N IV, and O V
http://academiccommons.columbia.edu/catalog/ac:157798
Fogle, M.; Bahati, E. M.; Bannister, M. E.; Vane, C. R.; Loch, S. D.; Pindzola, M. S.; Ballance, C, P,; Thomas, R. D.; Zhaunerchyk, V.; Bryans, P.; Mitthumsiri, W.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19371Mon, 18 Mar 2013 00:00:00 +0000We present recent measurements of absolute electron-impact ionization cross sections for Be-like C III, N IV, and O V forming Li-like C IV, N V, and O VI. The measurements were taken using the crossed-beams apparatus at Oak Ridge National Laboratory. A gas cell beam attenuation method was used to independently measure the metastable fractions present in the ion beams. The measured ionization cross sections were compared with calculations using the R-matrix with pseudostates and distorted-wave theoretical methods. Best agreement is found with the R-matrix with pseudostates cross sections results that account for the metastable fractions inferred from the gas attenuation measurements. We present a set of recommended rate coefficients for electron-impact single ionization from the ground state and metastable term of each ion.Astrophysics, Atomic physicsdws26Astronomy and AstrophysicsArticlesDielectronic Recombination of Fe XV Forming Fe XIV: Laboratory Measurements and Theoretical Calculations
http://academiccommons.columbia.edu/catalog/ac:157795
Lukic, D. V.; Schnell, M.; Savin, Daniel Wolf; Brandau, C.; Schmidt, E. W.; Bohm, S.; Muller, A.; Schippers, S.; Lestinsky, M.; Sprenger, F.; Wolf, A.; Altun, Z.; Badnell, N. R.http://hdl.handle.net/10022/AC:P:19370Mon, 18 Mar 2013 00:00:00 +0000We 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 ≲ 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 ≈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(1P1)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 kBTe ≥ 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%-28% smaller than our experimental results over this temperature range.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesImportance of Configuration Interaction for Accurate Atomic Data: Fluorescence Yields of K-Shell Vacancy, Lithium-Like Ions
http://academiccommons.columbia.edu/catalog/ac:157759
Savin, Daniel Wolf; Gorczyca, T. W.; Dumitriu, I.; Hasoǧlu, M. F. ; Korista, K. T.; Badnell, N. R. ; Manson, S. T.http://hdl.handle.net/10022/AC:P:19358Fri, 15 Mar 2013 00:00:00 +0000We demonstrate that the inclusion of configuration interaction (CI) results in significant values for the K-shell fluorescence yields of Li-like ions, which are zero in a single-configuration approach. Modeling codes for simulating supernova remnants under nonequilibrium ionization conditions or photoionized plasmas such as active galactic nuclei or X-ray binaries need to be updated accordingly. A two-parameter fitting formula for the fluorescence yields has been developed. The generality of important CI effects on atomic calculations is pointed out.Astrophysics, Atomic physics, Plasma physicsdws26Astronomy and AstrophysicsArticlesLaboratory Measurements of Fe XXIV L-Shell Line Emission
http://academiccommons.columbia.edu/catalog/ac:157756
Savin, Daniel Wolf; Beiersdorfer, P.; López-Urrutia, José Crespo; Decaux, V.; Gullikson, E. M.; Kahn, S. M.; Liedahl, Duane; Reed, K. J.; Widmann, K.http://hdl.handle.net/10022/AC:P:19357Fri, 15 Mar 2013 00:00:00 +0000Recent ASCA spectra exhibit discrepancies with the relative line intensities of various Fe XXIII and XXIV L-shell emission lines predicted by standard plasma emission codes. To address this issue, we have carried out a series of high-resolution, broadband measurements of Fe XXIV line emission using an electron beam ion trap facility. X-ray lines produced in the trap are detected and resolved using Bragg crystal spectrometers. We report measurements of 33 2 and 43 2 transitions, which result primarily from electron impact excitation. Overall, good agreement is found with distorted wave calculations.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesStrong LSJ Dependence of Fluorescence Yields: Breakdown of the Configuration-average Approximation
http://academiccommons.columbia.edu/catalog/ac:157762
Savin, Daniel Wolf; Hasoǧlu, M. F. ; Gorczyca, T. W.; Korista, K. T.; Manson, S. T.; Badnell, N. R.http://hdl.handle.net/10022/AC:P:19359Fri, 15 Mar 2013 00:00:00 +0000We demonstrate that the inclusion of configuration interaction (CI) results in significant values for the K-shell fluorescence yields of Li-like ions, which are zero in a single-configuration approach. Modeling codes for simulating supernova remnants under nonequilibrium ionization conditions or photoionized plasmas such as active galactic nuclei or X-ray binaries need to be updated accordingly. A two-parameter fitting formula for the fluorescence yields has been developed. The generality of important CI effects on atomic calculations is pointed out.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesLaboratory Measurements of Fe XXIV Line Emission: 3→2 Transitions Near Excitation Threshold
http://academiccommons.columbia.edu/catalog/ac:157765
Savin, Daniel Wolf; Gu, M. F.; Kahn, S. M.; Beiersdorfer, P.; Brown, G. V.; Liedahl, D. A.; Reed, K. J.; Bhalla , C. P.; Grabbe, S. R.http://hdl.handle.net/10022/AC:P:19360Fri, 15 Mar 2013 00:00:00 +0000Using the Electron Beam Ion Trap facility at Lawrence Livermore National Laboratory, we have measured relative cross sections for Fe XXIV line emission at electron energies between 0.7 and 3.0 keV. The measurements include line formation by direct electron impact excitation (DE), radiative cascades, resonant excitation (RE), and dielectronic recombination (DR) satellites with captured electrons in n≥5 levels. Good agreement with R-matrix and distorted wave calculations is found. In collisionally ionized plasmas, at temperatures near where the ion abundance peaks (kTe~1.7 keV), the RE contributions are found to be ≲5% of the line emission, while the DR satellites contribute ≲10%. While good agreement with state-of-the-art atomic physics calculations is found, there is less good agreement with existing spectral synthesis codes in common astrophysical use. For the Fe XXIV 3p3/2 → 2s1/2, 3p1/2 → 2s1/2, and 3d5/2 → 2p3/2 transitions, the synthesis code MEKAL underestimates the emissivity in coronal equilibrium by ~20% at temperatures near where the ion abundance peaks. In situations where the ionization balance is not solely determined by the electron temperature, RE and DR satellites may contribute a considerable fraction of the line emission.Astrophysics, Plasma physics, Atomic physicsdws26Astronomy and AstrophysicsArticlesA new 2D world for physicists?
http://academiccommons.columbia.edu/catalog/ac:130503
Morgante, Albertohttp://hdl.handle.net/10022/AC:P:10072Tue, 29 Mar 2011 00:00:00 +0000Atomic physics, Materials scienceItalian AcademyWorking papers