Academic Commons Search Results
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Academic Commons Search Resultsen-usCapriccio For Strings: Collision-Mediated Parallel Transport in Curved Landscapes and Conifold-Enhanced Hierarchies Among Mirror Quintic Flux Vacua
https://academiccommons.columbia.edu/catalog/ac:4xgxd25480
Eckerle, Kate10.7916/D85H7TH2Thu, 06 Jul 2017 22:14:05 +0000This dissertation begins with a review of Calabi-Yau manifolds and their moduli spaces, flux compactification largely tailored to the case of type IIb supergravity, and Coleman-De Luccia vacuum decay. The three chapters that follow present the results of novel research conducted as a graduate student.
Our first project is concerned with bubble collisions in single scalar field theories with multiple vacua. Lorentz boosted solitons traveling in one spatial dimension are used as a proxy to the colliding 3-dimensional spherical bubble walls. Recent work found that at sufficiently high impact velocities collisions between such bubble vacua are governed by "free passage" dynamics in which field interactions can be ignored during the collision, providing a systematic process for populating local minima without quantum nucleation.
We focus on the time period that follows the bubble collision and provide evidence that, for certain potentials, interactions can drive significant deviations from the free passage bubble profile, thwarting the production of a new patch with different field value. However, for simple polynomial potentials a fine-tuning of vacuum locations is required to reverse the free passage kick enough that the field in the collision region returns to the original bubble vacuum. Hence we deem classical transitions mediated by free passage robust.
Our second project continues with soliton collisions in the limit of relativistic impact velocity, but with the new feature of nontrivial field space curvature. We establish a simple geometrical interpretation of such collisions in terms of a double family of field profiles whose tangent vector fields stand in mutual parallel transport. This provides a generalization of the well-known limit in flat field space (free passage). We investigate the limits of this approximation and illustrate our analytical results with numerical simulations.
In our third and final project we investigate the distribution of field theories that arise from the low energy limit of flux vacua built on type IIb string theory compactified on the mirror quintic. For a large collection of these models, we numerically determine the distribution of Taylor coefficients in a polynomial expansion of each model's scalar potential to fourth order. We provide an analytic explanation of the proncounced hierarchies exhibited by the random sample of masses and couplings generated numerically. The analytic argument is based on the structure of masses in no scale supergravity and the divergence of the Yukawa coupling at the conifold point in the moduli space of the mirror quintic. Our results cast the superpotential vev as a random element whose capacity to cloud structure vanishes as the conifold is approached.Physics, Supergravity, Bubbles--Dynamics, Solitons--Mathematical modelsApplied Physics and Applied MathematicsThesesOutflows from compact objects in supernovae and novae
https://academiccommons.columbia.edu/catalog/ac:12jm63xsjm
Vlasov, Andrey Dmitrievich10.7916/D8KK9Q25Thu, 06 Jul 2017 22:13:36 +0000Originally thought of as a constant and unchanging place, the Universe is full of dramas of stars emerging, dying, eating each other, colliding, etc. One of the first transient phenomena noticed were called novae (the name means "new" in Latin). Years later, supernovae were discovered. Despite their names, both novae and supernovae are events in relatively old stars, with supernovae marking the point of stellar death. Known for thousands of years, supernovae and novae remain among the most studied events in our Universe. Supernovae strongly influence the circumstellar medium, enriching it with heavy elements and shocking it, facilitating star formation. Cosmic rays are believed to be accelerated in shocks from supernovae, with small contribution possibly coming from novae. Even though the basic physics of novae is understood, many questions remain unanswered. These include the geometry of the ejecta, why some novae are luminous radio or gamma-ray sources and others are not, what is the ultimate fate of recurrent novae, etc.
Supernova explosions are the primary sources of elements heavier than hydrogen and helium. The elements up to nuclear masses A around 100 can form through successive nuclear fusion in the cores of stars starting with hydrogen. Beyond iron, the fusion becomes endothermic instead of exothermic. In addition, for these nuclear masses the temperatures required to overcome the Coulomb barriers are so high that the nuclei are dissociated into alpha particles and free nucleons. Hence all elements heavier than A around 100 should have formed by some other means. These heavier nuclear species are formed by neutron capture on seed nuclei close to or heavier than iron-group nuclei. Depending on the ratio between neutron-capture timescale and beta-decay timescale, neutron-capture processes are called rapid or slow (r- and s-processes, respectively). The s-process, which occurs near the valley of stable isotopes, terminates at Bi (Z=83), because after Bi there is a gap of four elements with no stable isotopes (Po, At, Rn, Ac) until we come to stable Th. The significant abundance of Th and U in our Universe therefore implies the presence of a robust source of r-process. The astrophysical site of r-process is still under debate. Here we present a study of a candidate site for r-process, neutrino-heated winds from newly-formed strongly magnetized, rapidly rotating neutron stars ("proto-magnetars"). Even though we find such winds are incapable of synthesizing the heaviest r-process elements like U and Th, they produce substantial amounts of weak r-process (38<Z<47) elements. This may lead to a unique imprint of rotation and magnetic fields compared to such yields from otherwise analogous slowly rotating non-magnetized proto-neutron stars.
Novae explosions are not as powerful as those of supernovae, but they occur much more frequently. The standard model of novae assumes a one-stage ejection of mass from the white dwarf following thermonuclear runaway. The discovery by the Fermi space telescope of gamma-rays from classical novae made the existence of shocks in novae outflows evident. The presence of shocks in novae was considered well before the discovery of gamma-ray emission; however, little previous theoretical work acknowledged the overwhelming effect of shocks on observed emission and ejecta geometry. Here we present the calculations of synchrotron radio emission from the shocks as they propagate down the density gradient and peak at the timescale of a few months. The model satisfactory fits observations and has several implications for the physics of novae.Astrophysics, Physics, Supernovae, Synchrotron radiationPhysicsThesesHigh-precision spectroscopy of ultracold molecules in an optical lattice
https://academiccommons.columbia.edu/catalog/ac:205274
McGuyer, B. H.; McDonald, Mickey; Iwata, Geoffrey Zerbinatti; Tarallo, M. G.; Grier, A. T.; Apfelbeck, F.; Zelevinsky, Tanya10.7916/D8HX1D5KWed, 05 Jul 2017 13:41:35 +0000The study of ultracold molecules tightly trapped in an optical lattice can expand the frontier of precision measurement and spectroscopy, and provide a deeper insight into molecular and fundamental physics. Here we create, probe, and image microkelvin 88Sr2 molecules in a lattice, and demonstrate precise measurements of molecular parameters as well as coherent control of molecular quantum states using optical fields. We discuss the sensitivity of the system to dimensional effects, a new bound-to-continuum spectroscopy technique for highly accurate binding energy measurements, and prospects for new physics with this rich experimental system.Optical lattices, Photodissociation, Spectrum analysis, Ultracold neutrons, Physicsmpm2153, gzi2000, tz2142PhysicsArticlesHigh-Speed imaging of the plasma response to resonant magnetic perturbations in HBT-EP
https://academiccommons.columbia.edu/catalog/ac:204442
Angelini, Sarah M.; Levesque, Jeffrey; Mauel, Michael E.; Navratil, Gerald10.7916/D8JS9QTSWed, 05 Jul 2017 13:40:58 +0000A Phantom v7.3 fast digital camera was used to study visible light fluctuations in the High Beta Tokamak–Extended Pulse (HBT–EP). This video data is the first to be used to analyze and understand the behavior of long wavelength kink perturbations in a wall-stabilized tokamak. The light was mostly comprised of Dα 656 nm light. Profiles of the plasma light at the midplane were hollow with a radial scale length of approximately 4 cm at the plasma edge. The fast camera was also used to measure the plasma's response to applied helical magnetic perturbations. The programmed toroidal phase angle of the resonant magnetic perturbation (RMP) was directly inferred from the resulting images of the plasma response. The plasma response and the intensity of the RMP were compared under different conditions. The resulting amplitude correlations are consistent with previous measurements of the static response using an array of magnetic sensors.Plasma (Ionized gases), Controlled fusion, Nuclear fusion, Plasma spectroscopy, Tokamaks, Physicsjpl2131, mem4, gan2Applied Physics and Applied MathematicsArticlesLithium-Excess Research of Cathode Material Li2MnTiO4 for Lithium-Ion Batteries
https://academiccommons.columbia.edu/catalog/ac:194325
Zhang, Xinyi; Yang, Le; Hao, Feng; Chen, Haosen; Yang, Meng; Fang, Daining10.7916/D8TM79ZMFri, 30 Jun 2017 00:46:16 +0000Lithium-excess and nano-sized Li2+xMn1−x/2TiO4 (x = 0, 0.2, 0.4) cathode materials were synthesized via a sol-gel method. The X-ray diffraction (XRD) experiments indicate that the obtained main phases of Li2.0MnTiO4 and the lithium-excess materials are monoclinic and cubic, respectively. The scanning electron microscope (SEM) images show that the as-prepared particles are well distributed and the primary particles have an average size of about 20–30 nm. The further electrochemical tests reveal that the charge-discharge performance of the material improves remarkably with the lithium content increasing. Particularly, the first discharging capacity at the current of 30 mA g−1 increases from 112.2 mAh g−1 of Li2.0MnTiO4 to 187.5 mAh g−1 of Li2.4Mn0.8TiO4. In addition, the ex situ XRD experiments indicate that the monoclinic Li2MnTiO4 tends to transform to an amorphous state with the extraction of lithium ions, while the cubic Li2MnTiO4 phase shows better structural reversibility and stability.Titanates, Phase transformations (Statistical physics), Cathodes, Lithium ion batteries, Electrical engineering, Physics, Chemistry, Physical and theoreticalfh2314Earth and Environmental EngineeringArticlesObservation of Superheating of Si at the Si/SiO2 Interface in Pulsed-laser irradiated Si Thin Films
https://academiccommons.columbia.edu/catalog/ac:193322
Wang, Jin Jimmy; Limanov, Alexander B.; Wang, Ying; Im, James Sungbin10.7916/D8KH0N44Fri, 30 Jun 2017 00:46:03 +0000Substantial superheating of single-crystal Si films at and near the bottom Si/SiO2 interface was observed. This was accomplished via back-side irradiation of a (100) single-crystal Si film on a quartz substrate using an excimer-laser pulse. The spatiotemporal details of the melting transition were tracked in situ using surface-side and substrate-side transient reflectance measurements, and the one-dimensional thermal profile evolution within the solid film during the heating period was numerically computed using the experimentally extracted temporal profile of the incident beam and temperature-dependent optical and thermal parameters of the materials. A simple lower-bound estimation identifies that superheating in excess of 100 K was attained within Si along the bottom (100)-Si/SiO2 interface even at moderate beam energy densities.Excimer lasers, Heat, Thermodynamics, Silicon crystals, High temperatures, Physics, Materials sciencejjw2154, abl24, yw2323, ji12Applied Physics and Applied MathematicsConference postersObservation of Superheating of Si at the Si/SiO2 Interface in Pulsed-laser irradiated Si Thin Films
https://academiccommons.columbia.edu/catalog/ac:193233
Wang, Jin Jimmy; Limanov, Alexander B.; Wang, Ying; Im, James Sungbin10.7916/D8F76C9BFri, 30 Jun 2017 00:46:02 +0000Substantial superheating of single-crystal Si films at and near the bottom Si/SiO2 interface was observed. This was accomplished via back-side irradiation of a (100) single-crystal Si film on a quartz substrate using an excimer-laser pulse. The spatiotemporal details of the melting transition were tracked in situ using surface-side and substrate-side transient reflectance measurements, and the one-dimensional thermal profile evolution within the solid film during the heating period was numerically computed using the experimentally extracted temporal profile of the incident beam and temperature-dependent optical and thermal parameters of the materials. A simple lower-bound estimation identifies that superheating in excess of 100 K was attained within Si along the bottom (100)-Si/SiO2 interface even at moderate beam energy densities.Thin films, Nanostructured materials, Materials at high temperatures, Silicon, Silicon crystals, High temperatures, Physics, Microphysicsjjw2154, abl24, yw2323, ji12Applied Physics and Applied MathematicsArticlesOn the stress dependence of the earthquake b value
https://academiccommons.columbia.edu/catalog/ac:191744
Scholz, Christopher H.10.7916/D8VQ323BThu, 29 Jun 2017 17:10:57 +0000Laboratory experiments have shown that the b value in the size distribution of acoustic emission events decreases linearly with differential stress. There have been a number of observations that indicate that this relation may also hold for earthquakes. Here using a simple frictional strength model for stresses in the continental lithosphere combined with earthquake b values measured as a function of depth in a wide variety of tectonic regions, we verify and calibrate that relation, finding b = 1.23 ± 0.06 − (0.0012 ± 0.0003)(σ1 − σ3), where the stress difference (σ1 − σ3) is in megapascal. For subduction zones, we find that b value correlates linearly with the slab pull force and with the net reduction of plate interface normal force, both of which also indicate a negative linear relation between b value and differential stress.Geology, Structural, Seismic waves--Mathematical models, Seismic waves--Measurement, Seismometry, Geology, Geophysics, Physicschs2Lamont-Doherty Earth ObservatoryArticlesCitizen Sensors for SHM: Use of Accelerometer Data from Smartphones
https://academiccommons.columbia.edu/catalog/ac:189133
Feng, Maria Q.; Fukuda, Yoshio; Mizuta, Masato; Ozer, Ekin10.7916/D80C4V6CThu, 29 Jun 2017 17:09:56 +0000Ubiquitous smartphones have created a significant opportunity to form a low-cost wireless Citizen Sensor network and produce big data for monitoring structural integrity and safety under operational and extreme loads. Such data are particularly useful for rapid assessment of structural damage in a large urban setting after a major event such as an earthquake. This study explores the utilization of smartphone accelerometers for measuring structural vibration, from which structural health and post-event damage can be diagnosed. Widely available smartphones are tested under sinusoidal wave excitations with frequencies in the range relevant to civil engineering structures. Large-scale seismic shaking table tests, observing input ground motion and response of a structural model, are carried out to evaluate the accuracy of smartphone accelerometers under operational, white-noise and earthquake excitations of different intensity. Finally, the smartphone accelerometers are tested on a dynamically loaded bridge. The extensive experiments show satisfactory agreements between the reference and smartphone sensor measurements in both time and frequency domains, demonstrating the capability of the smartphone sensors to measure structural responses ranging from low-amplitude ambient vibration to high-amplitude seismic response. Encouraged by the results of this study, the authors are developing a citizen-engaging and data-analytics crowdsourcing platform towards a smartphone-based Citizen Sensor network for structural health monitoring and post-event damage assessment applications.Physics, Civil engineering, Mechanical engineeringmqf2101, yf2290, mm4230, eo2327Civil Engineering and Engineering MechanicsArticlesAnisotropy of a Tensorial Bishop’s Coefficient for Wetted Granular Materials
https://academiccommons.columbia.edu/catalog/ac:188654
Wang, Kun; Sun, WaiChing10.7916/D8VX0FT7Thu, 29 Jun 2017 16:41:51 +0000The objective of this research is to use grain-scale numerical simulations to analyze the evolution of stress anisotropy exhibited in wetted granular matter. Multiphysical particulate simulations of unsaturated granular materials were conducted to analyze how the interactions of contact force chains and liquid bridges affect macroscopic responses under various suction pressure and loading histories. To study how the formation and rupture of liquid bridges affect the mechanical responses of wetted granular materials, a series of suction-controlled triaxial tests were conducted with two grain assemblies, one composed of large particles of similar sizes, the other composed of a mixture of large particles with significant amount of fines. The results indicate that capillary stresses are anisotropic in both sets of specimens, and that stress anisotropy is more significant in granular assemblies filled with fine particles. A generalized tensorial Bishop’s coefficient is introduced to analyze the connections between microstructural attributes and macroscopic responses. Numerical simulations presented in this paper indicate that the principal values and directions of this Bishop’s coefficient tensor are path dependent.Materials science, Geophysics, Physicskw2534, ws2414Civil Engineering and Engineering MechanicsArticlesPaul Drude’s Prediction of Nonreciprocal Mutual Inductance for Tesla Transformers
https://academiccommons.columbia.edu/catalog/ac:183558
McGuyer, Bart H.10.7916/D83F4NG3Thu, 29 Jun 2017 03:42:49 +0000Inductors, transmission lines, and Tesla transformers have been modeled with
lumped-element equivalent circuits for over a century. In a well-known paper from
1904, Paul Drude predicts that the mutual inductance for an unloaded Tesla
transformer should be nonreciprocal. This historical curiosity is mostly forgotten
today, perhaps because it appears incorrect. However, Drude’s prediction is shown
to be correct for the conditions treated, demonstrating the importance of constraints
in deriving equivalent circuits for distributed systems. The predicted nonreciprocity
is not fundamental, but instead is an artifact of the misrepresentation of energy by
an equivalent circuit. The application to modern equivalent circuits is discussed.Physicsbhm2113ArticlesCumulus Microphysics and Climate Sensitivity
https://academiccommons.columbia.edu/catalog/ac:183320
Del Genio, Anthony D.; Kovari, William; Yao, Mao-Sung; Jonas, Jeffrey10.7916/D8KS6QC4Thu, 29 Jun 2017 03:38:03 +0000Precipitation processes in convective storms are potentially a major regulator of cloud feedback. An
unresolved issue is how the partitioning of convective condensate between precipitation-size particles that fall out of updrafts and smaller particles that are detrained to form anvil clouds will change as the climate warms. Tropical Rainfall Measuring Mission (TRMM) observations of tropical oceanic convective storms indicate higher precipitation efficiency at warmer sea surface temperature (SST) but also suggest that cumulus anvil sizes, albedos, and ice water paths become insensitive to warming at high temperatures. International Satellite Cloud Climatology Project (ISCCP) data show that instantaneous cirrus and deep convective cloud fractions are positively correlated and increase with SST except at the highest temperatures, but are sensitive to variations in large-scale vertical velocity. A simple conceptual model based on a Marshall–Palmer drop size distribution, empirical terminal velocity–particle size relationships, and assumed cumulus updraft speeds reproduces the observed tendency for detrained condensate to approach a limiting value at high SST. These results suggest that the climatic behavior of observed tropical convective clouds is intermediate between the extremes required to support the thermostat and adaptive iris hypotheses.Climatic changes, Physics, Ecologyadd1, wk14, jaj28Goddard Institute for Space Studies, Center for Climate Systems ResearchArticlesNear-field radiative transfer between two unequal sized spheres with large size disparities
https://academiccommons.columbia.edu/catalog/ac:179718
Sasihithlu, Karthik; Narayanaswamy, Arvind10.7916/D8X63KMQThu, 29 Jun 2017 03:05:42 +0000We compute near-field radiative transfer between two spheres of unequal radii R1 and R2 such that R2 ≲ 40R1. For R2 = 40R1, the smallest gap to which we have been able to compute radiative transfer is d = 0.016R1. To accomplish these computations, we have had to modify existing methods for computing near-field radiative transfer between two spheres in the following ways: (1) exact calculations of coefficients of vector translation theorem are replaced by approximations valid for the limit d ≪ R1, and (2) recursion relations for a normalized form of translation coefficients are derived which enable us to replace computations of spherical Bessel and Hankel functions by computations of ratios of spherical Bessel or spherical Hankel functions. The results are then compared with the predictions of the modified proximity approximation.Physicsks2683, an2288Mechanical EngineeringArticlesHelium-ion-induced radiation damage in LiNbO₃ thin-film electro-optic modulators
https://academiccommons.columbia.edu/catalog/ac:179745
Huang, Hsu-Cheng; Dadap, Jr., Jerry I.; Malladi, Girish; Kymissis, Ioannis; Bakhru, Hassaram; Osgood, Jr., Richard M.10.7916/D84Q7SPNThu, 29 Jun 2017 03:02:44 +0000Helium-ion-induced radiation damage in a LiNbO₃-thin-film (10 μm-thick) modulator is experimentally investigated. The results demonstrate a degradation of the device performance in the presence of He⁺ irradiation at doses of ≥ 1016 cm⁻². The experiments also show that the presence of the He⁺ stopping region, which determines the degree of overlap between the ion-damaged region and the guided optical mode, plays a major role in determining the degree of degradation in modulation performance. Our measurements showed that the higher overlap can lead to an additional ~5.5 dB propagation loss. The irradiation-induced change of crystal-film anisotropy(nₒ−nₑ )of ~36% was observed for the highest dose used in the experiments. The relevant device extinction ratio, VπL, and device insertion loss, as well the damage mechanisms of each of these parameters are also reported and discussed.Electrical engineering, Physicshh2362, jid5, ik2174, rmo1Electrical EngineeringArticlesMagma migration and magmatic solitary waves in 3-D
https://academiccommons.columbia.edu/catalog/ac:177438
Wiggins, Chris H.; Spiegelman, Marc W.10.7916/D8Z31X5JWed, 28 Jun 2017 20:57:06 +0000Numerical studies of fluid flow in the mantle suggest that magma migration is an inherently time-dependent process that produces magmatic solitary waves from obstructions in melt flux. Previous work has considered one and two dimensional problems. Here we present the results of three dimensional calculations that utilize a new, efficient multigrid scheme. We demonstrate that one and two dimensional solitary waves are unstable and break up into sets of 3-D solitary waves which are perfectly spherical when propagating through a uniform porosity medium. While these waves are not solitons, their non-linear interactions are qualitatively similar. The solitary waves are highly opportunistic and establish efficient pathways for migration by linking up with nearby waves. When the initial condition is a random distribution of porosity, the porosity structure can organize into elongate, time-dependent channels formed from chains of solitary waves. These results are natural consequences of the assumptions that the matrix is permeable and viscously deformable. We suggest that solitary waves are likely to exist in the mantle and may contribute to the episodicity of mantle magmatism.Physics, Geophysicschw2, mws6Applied Physics and Applied Mathematics, Earth and Environmental SciencesArticlesMicro-Raman spectroscopic visualization of lattice vibrations and strain in He+- implanted single-crystal LiNbO3
https://academiccommons.columbia.edu/catalog/ac:172060
Huang, Hsu-Cheng; Dadap, Jerry I.; Herman, Irving P.; Bakhru, Hassaram; Osgood, Jr., Richard M.10.7916/D8BC3WKFWed, 28 Jun 2017 20:28:52 +0000Scanning micro-Raman spectroscopy has been utilized to image and investigate strain in He+-implanted congruent LiNbO3 samples. By using abruptly patterned implanted samples, we show that the spatial two-dimensional mapping of the Raman spectral peaks can be used to image the strain distribution and determine its absolute magnitude. We demonstrate that both short- and long-range length-scale in-plane and out-of-plane strain and stress states can be determined using the secular equations of phonon-deformation-potential theory. We also show that two-dimensional Raman imaging can be used to visualize the relaxation of strain in the crystal during low-temperature annealing.Electrical engineering, Physicshh2362, jid5, iph1, rmo1ArticlesOrigin of defect-related green emission from ZnO nanoparticles: effect of surface modification
https://academiccommons.columbia.edu/catalog/ac:190428
Gong, Yinyan; Andelman, Tamar; Neumark, Gertrude; O’Brien, Stephen; Kuskovsky, Igor10.7916/D8125R3CWed, 28 Jun 2017 20:12:59 +0000We investigated the optical properties of colloidal-synthesized ZnO spherical nanoparticles prepared from 1-octadecene (OD), a mixture of trioctylamine (TOA) and OD (1:10), and a mixture of trioctylphosphine oxide (TOPO) and OD (1:12). It is found that the green photoluminescence (PL) of samples from the mixture of TOA/ OD and TOPO/OD is largely suppressed compared with that from pure OD. Moreover, it is found that all spherical nanoparticles have positive zeta potential, and spherical nanoparticles from TOA/OD and TOPO/OD have a smaller zeta potential than those from OD. A plausible explanation is that oxygen vacancies, presumably located near the surface, contribute to the green PL, and the introduction of TOA and TOPO will reduce the density of oxygen vacancies near the surfaces. Assuming that the green emission arises due to radiative recombination between deep levels formed by oxygen vacancies and free holes, we estimate the size of optically active spherical nanoparticles from the spectral energy of the green luminescence. The results are in good agreement with results from TEM. Since this method is independent of the degree of confinement, it has a great advantage in providing a simple and practical way to estimate the size of spherical nanoparticles of any size. We would like to point out that this method is only
applicable for samples with a small size distribution.Photoluminescence, Nanofluids, Spectral energy distribution, Nanoparticles, Nanoscience, Physics, Chemistry, Physical and theoreticalyg2002Applied Physics and Applied MathematicsArticlesTheory of thermal nonequilibrium entropy in near-field thermal radiation
https://academiccommons.columbia.edu/catalog/ac:166229
Narayanaswamy, Arvind; Zheng, Yi10.7916/D80C55XWWed, 28 Jun 2017 17:11:55 +0000We propose a theoretical formalism to evaluate the entropy density and entropy flux that takes into account near-field effects, i.e., interference, diffraction, and tunneling of waves. Using the fluctuation-dissipation theorem, expressions for entropy density and entropy flux in a vacuum cavity between planar multilayered media are derived in terms of local density of photons, local density of accessible microscopic states, and velocity of energy transmission. The proposed method is used to determine the maximum work that can be extracted and a thermodynamic limit of the energy conversion efficiency that can be obtained in near-field thermal radiation.Mechanical engineering, Nanoscience, Physicsan2288, yz2308Mechanical EngineeringArticlesThe Effect of a Hadley Circulation on the Propagation and Reflection of
Planetary Waves in a Simple One-Layer Model
https://academiccommons.columbia.edu/catalog/ac:167050
Esler, J. Gavin; Polvani, Lorenzo M.; Plumb, R. Alan10.7916/D8086GFPWed, 28 Jun 2017 16:59:34 +0000The effect of a simple representation of the Hadley circulation on the propagation and nonlinear reflection of planetary-scale Rossby waves in the winter hemisphere is investigated numerically in a single-layer shallow-water model.
In the first instance, waves are forced by a zonal wavenumber three topography centered in the extratropics. In the linear limit the location of the low-latitude critical line at which the waves are absorbed is displaced poleward by the Hadley circulation. At finite forcing amplitude the critical layer regions where the waves break are found to be displaced poleward by a similar distance. The Hadley circulation is also found to inhibit the onset of nonlinear reflection by increasing the dissipation of wave activity in the critical layer.
Second, for waves generated by an isolated mountain, the presence of the Hadley circulation further inhibits nonlinear reflection by generating a strong westerly flux of wave activity within the critical layer. This westerly flux is shown to be largely advective and is explained by the poleward displacement of the critical line into the region of westerly flow. A simple expression is derived for the minimum zonal wind strength allowing propagation in the case of a quasigeostrophic β-plane flow when the mean meridional wind ̅υ greater than 0.Geophysics, Atmosphere, Physicslmp3Applied Physics and Applied MathematicsArticlesNonlinear Geostrophic Adjustment, Cyclone/Anticyclone Asymmetry, and Potential Vorticity Rearrangement
https://academiccommons.columbia.edu/catalog/ac:167047
Kuo, Allen C.; Polvani, Lorenzo M.10.7916/D8VM4PD5Wed, 28 Jun 2017 16:59:34 +0000Within the context of the rotating shallow water equations, it is shown how initially unbalanced states possessing certain symmetries dynamically evolve to lose those symmetries during nonlinear geostrophic adjustment. Using conservation law methods, it is demonstrated that the adjustment of equal and opposite (circular) mass imbalances results in a balanced end state where cyclones are stronger than anticyclones; the reverse holds true for momentum imbalances. In both cases, the degree of this asymmetry is shown to be directly proportional to the amount of initial imbalance (a measure of the nonlinearity occurring during time-dependent adjustment). On the other hand, the degree of asymmetry is maximal for imbalances of Rossby deformation scale. As for the potential vorticity, it is shown that its final profile can be noticeably different from its initial one; from an Eulerian perspective, this rearrangement is not confined to uniform shifts of potential vorticity fronts. Direct 2D numerical initial value problems confirm the asymmetry in the predicted final states and establish a relatively fast time scale for adjustment to complete. The robustness of these results is confirmed by studying, in addition, the adjustment of elliptical mass imbalances. The numerical integrations reveal that, during geostrophic adjustment, potential vorticity rearrangement occurs irreversibly on a fast wave time scale.Physics, Geophysics, Mathematicslmp3Applied Physics and Applied MathematicsArticlesWave-Vortex Interaction in Rotating Shallow Water. Part 1. One Space Dimension
https://academiccommons.columbia.edu/catalog/ac:167056
Kuo, Allen C.; Polvani, Lorenzo M.10.7916/D8N3072RWed, 28 Jun 2017 16:59:09 +0000Using a physical space (i.e. non-modal) approach, we investigate interactions between fast inertio-gravity (IG) waves and slow balanced flows in a shallow rotating fluid. Specifically, we consider a train of IG waves impinging on a steady, exactly balanced vortex. For simplicity, the one-dimensional problem is studied first; the limitations of one-dimensionality are offset by the ability to define balance in an exact way. An asymptotic analysis of the problem in the small-amplitude limit is performed to demonstrate the existence of interactions. It is shown that these interactions are not confined to the modification of the wave field by the vortex but, more importantly, that the waves are able to alter in a non-trivial way the potential vorticity associated with that vortex. Interestingly, in this one-dimensional problem, once the waves have traversed the vortex region and have propagated away, the vortex exactly recovers its initial shape and thus bears no signature of the interaction. Furthermore, we prove this last result in the case of arbitrary vortex and wave amplitudes. Numerical integrations of the full one-dimensional shallow-water equations in strongly nonlinear regimes are also performed: they confirm that time-dependent interactions exist and increase with wave amplitude, while at the final state the vortex bears no sign of the interaction. In addition, they reveal that cyclonic vortices interact more strongly with the wave field than anticyclonic ones.Geophysics, Mathematics, Physicslmp3Applied Physics and Applied MathematicsArticlesTime-Dependent Fully Nonlinear Geostrophic Adjustment
https://academiccommons.columbia.edu/catalog/ac:167071
Kuo, Allen C.; Polvani, Lorenzo M.10.7916/D8GB2F4RWed, 28 Jun 2017 16:58:43 +0000Shock-capturing numerical methods are employed to integrate the fully nonlinear, rotating 1D shallow-water equations starting from steplike nongeostrophic initial conditions (a Rossby adjustment problem). Such numerical methods allow one to observe the formation of multiple bores during the transient adjustment process as well as their decay due to rotation. It is demonstrated that increasing the rotation and/or the nonlinearity increases the rate of decay. Additionally, the time required for adjustment to be completed and its dependence on nonlinearity is examined; this time is found to be highly measure dependent. Lastly, the final adjusted state of the system is observed through long time integrations. Although the bores that form provide a mechanism for dissipation, their decay results in a final state in very good agreement with the one computed by well-known (dissipationless) conservation methods.Physics, Geophysics, Mathematicslmp3Applied Physics and Applied MathematicsArticlesRossby Wave Breaking, Microbreaking, Filamentation, and Secondary Vortex Formation: The Dynamics of a Perturbed Vortex
https://academiccommons.columbia.edu/catalog/ac:167170
Polvani, Lorenzo M.; Plumb, R. Alan10.7916/D8KW5CXTWed, 28 Jun 2017 16:58:26 +0000The behavior of an isolated vortex perturbed by topographically forced Rossby waves is studied using the method of Contour Dynamics. For a single-contour vortex a distinct forcing threshold exists above which the wave breaks in a dynamically significant way, leading to a disruption of the vortex. This breaking is distinguished from the process of weak filamentary breaking described by Dritschel and classified here as microbreaking; the latter occurs in nondivergent flow even at very small forcing amplitudes but does not affect the vortex in a substantial manner. In cases with finite Rossby deformation radius (comparable with the vortex radius) neither breaking nor microbreaking occurs below the forcing threshold. In common with previous studies using high-resolution spectral models, the vortex is not diluted by intrusion of outside air, except during remerger with a secondary vortex shed previously from the main vortex during a breaking event. The kinematics of the breaking process and of the vortex interior and the morphology of material ejected from the vortex are described. When the Rossby radius is finite there is substantial mixing in the deep interior of the vortex, even when the vortex is only mildly disturbed. Implications for the stratospheric polar vortex are discussed.Atmosphere, Atmosphere, Upper, Physicslmp3Applied Physics and Applied MathematicsArticlesTwo-Layer Geostrophic Vortex Dynamics. Part 2. Alignment and Two-Layer V-States
https://academiccommons.columbia.edu/catalog/ac:167173
Polvani, Lorenzo M.10.7916/D8G44N6TWed, 28 Jun 2017 16:57:37 +0000The process of alignment, a new fundamental interaction between vortices in a stratified and rapidly rotating fluid, is defined and studied in detail in the context of the two-layer quasi-geostrophic model. Alignment occurs when two vortices in different density layers coalesce by reducing their horizontal separation. It is found that only vortices whose radii are comparable with or larger than the Rossby deformation radius can align. In the same way as the merger process (in a single two dimensional layer) is related to the reverse energy cascade of two-dimensional turbulence, geostrophic potential vorticity alignment is related the barotropic-to baroclinic energy cascade of geostrophic turbulence in two layers. It is also shown how alignment is intimately connected with the existence of two-layer doubly connected geostrophic potential vorticity equilibria (V-states), for which the analysis of the geometry of the stream function in the corotating frame is found to be a crucial diagnostic. The finite-area analogues of the hetons of Hogg and Stommel (1985) are also determined : they consist of a propagating pair of opposite-signed potential vorticity patches located in different layers.Atmosphere, Physics, Mathematicslmp3Applied Physics and Applied MathematicsArticlesWave–Wave Interaction of Unstable Baroclinic Waves
https://academiccommons.columbia.edu/catalog/ac:167188
Pedlosky, Joseph; Polvani, Lorenzo M.10.7916/D8TD9V7HWed, 28 Jun 2017 16:57:05 +0000Two slightly unstable baroclinic waves in the two-layer Phillips model are allowed to interact with each other as well as the mean flow. A theory for small dissipation rates is developed to examine the role of wave–wave interaction in the dynamics of vacillation and aperiodicity in unstable systems.
It is shown that the form of the dissipation mechanism as well as the overall dissipation timescale determines the nature of the dynamics. In particular, dissipation proportional to potential vorticity is shown to expunge amplitude vacillation due to wave–mean flow interactions.
Wave–wave interaction, however, can yield amplitude vacillation. As the dissipation is decreased, the solutions evolve from steady waves (although propagating) to periodic vacillation until finally at small dissipation rates, chaotic behavior is obtained.
This occurs in a range of relative growth rates of the two waves which depends on the strength of the wave–wave and wave–mean flow interactions.Atmosphere, Mathematics, Physicslmp3Applied Physics and Applied MathematicsArticlesThe Effect of Dissipation on Spatially Growing Nonlinear Baroclinic Waves
https://academiccommons.columbia.edu/catalog/ac:167185
Polvani, Lorenzo M.; Pedlosky, J.10.7916/D8Z60KZCWed, 28 Jun 2017 16:57:05 +0000The question of convective (i.e., spatial) instability of baroclinic waves on an f-plane is studied in the context of the two-layer model. The viscous and inviscid marginal curves for linear convective instability are obtained. The finite-amplitude problem shows that when dissipation is O(1) it acts to stabilize the waves that are of Eady type. For very small dissipation the weakly nonlinear analysis reveals that at low frequencies, contrary to what is known to occur in the temporal problem, in addition to the baroclinic component a barotropic correction to the “mean” flow is generated by the nonlinearities, and spatial equilibration occurs provided the ratio of shear to mean flow does not exceed some critical value. In the same limit, the slightly dissipative nonlinear dynamics reveals the presence of large spatial vacillations immediately downstream of the source, even if asymptotically (i.e., very far away from the source) the amplitudes are found to reach steady values. No case of period doubling or aperiodic behavior was found. The results obtained seem to be qualitatively independent of the form chosen to model the dissipation.Atmosphere, Physics, Mathematicslmp3Applied Physics and Applied MathematicsArticlesFilamentation of Unstable Vortex Structures via Separatrix Crossing: A Quantitative Estimate of Onset Time
https://academiccommons.columbia.edu/catalog/ac:167182
Polvani, Lorenzo M.; Flierl, G. R.; Zabusky, N. J.10.7916/D82Z13FRWed, 28 Jun 2017 16:57:05 +0000The onset of filamentation for compact vortex structures in two-dimensional incompressible flows is elucidated. An estimate is presented for the filamentation time of an unstably perturbed Kirchhoff ellipse, obtained from a linear analysis of the geometry of the instantaneous corotating streamfunction.Mathematics, Physicslmp3Applied Physics and Applied MathematicsArticlesTwo-Layer Geostrophic Vortex Dynamics. Part 1. Upper-Layer V-States and Merger
https://academiccommons.columbia.edu/catalog/ac:167179
Polvani, Lorenzo M.; Flierl, G. R.; Zabusky, N. J.10.7916/D86Q1V53Wed, 28 Jun 2017 16:57:05 +0000We generalize the methods of two-dimensional contour dynamics to study a two-layer rotating fluid that obeys the quasi-geostrophic equations. We consider here only the case of a constant-potential-vorticity lower layer. We derive equilibrium solutions for monopolar (rotating) and dipolar (translating) geostrophic vortices in the upper layer, and compare them with the Euler case. We show that the equivalent barotropic (infinite lower layer) case is a singular limit of the two-layer system. We also investigate the effect of a finite lower layer on the merger of two regions of equal-sign potential vorticity in the upper layer. We discuss our results in the light of the recent laboratory experiments of Griffiths and Hopfinger (1986). The process of filamentation is found to be greatly suppressed for equivalent barotropic dynamics on scales larger than the radius of deformation. We show that the variation of the critical initial distance for merger as a function of the radius of deformation and the ratio of the layers at rest is closely related to the existence of vortex-pair equilibria and their geometrical properties.Mathematics, Physics, Atmospherelmp3Applied Physics and Applied MathematicsArticlesChaotic Lagrangian Trajectories around an Elliptical Vortex Patch Embedded in a Constant and Uniform Background Shear Flow
https://academiccommons.columbia.edu/catalog/ac:167176
Polvani, Lorenzo M.; Wisdom, J.10.7916/D8BG2KWDWed, 28 Jun 2017 16:57:05 +0000The Lagrangian flow around a Kida vortex [J. Phys. Soc. Jpn. 5 0, 3517 (1981)], an elliptical two‐dimensional vortex patch embedded in a uniform and constant background shear, is described by a nonintegrable two‐degree‐of‐freedom Hamiltonian. For small values of shear, there exist large chaotic zones surrounding the vortex, often much larger than the vortex itself and extremely close to its boundary. Motion within the vortex is integrable. Implications for two‐dimensional turbulence are discussed.Physics, Mathematicslmp3Applied Physics and Applied MathematicsArticlesGeneralized Kirchhoff Vortices
https://academiccommons.columbia.edu/catalog/ac:167191
Polvani, Lorenzo M.; Flierl, G. R.10.7916/D8PN93H5Wed, 28 Jun 2017 16:56:46 +0000A family of exact solutions of the Euler equations is presented: they are generalizations of the Kirchhoff vortex to N confocal ellipses. Special attention is given to the case N=2, for which the stability is analyzed with a method similar to the one used by Love [Proc. London Math. Soc. 1, XXV 18 (1893)] for the Kirchhoff vortex. The results are compared with those for the corresponding circular problem.Mathematics, Physicslmp3Applied Physics and Applied MathematicsArticlesProduction of Heavy Particles by Protons on Protons
https://academiccommons.columbia.edu/catalog/ac:167194
Afek, Y.; Margolis, B.; Polvani, Lorenzo M.10.7916/D8JW8BSFWed, 28 Jun 2017 16:56:46 +0000We calculate the production of heavy particles in the multi-GeV energy range using parton-model and statistical considerations. We discuss both central production and fragmentation. Our picture has implications for the question of the existence of a limiting temperature in hadron interactions.Physics, Mathematicslmp3Applied Physics and Applied MathematicsArticlesInitiation propagation and termination of elastodynamic ruptures
associated with segmentation of faults and shaking hazard
https://academiccommons.columbia.edu/catalog/ac:162517
Shaw, Bruce E.10.7916/D8HM5KFNTue, 27 Jun 2017 20:05:06 +0000Using a model of a complex fault system, we examine the initiation, propagation, and termination of ruptures and their relationship to fault geometry and shaking hazard. We find concentrations of epicenters near fault step overs and ends; concentrations of terminations near fault ends; and persistent propagation directivity effects. Taking advantage of long sequences of dynamic events, we directly measure shaking hazards, such as peak ground acceleration exceedance probabilities, without need for additional assumptions. This provides a new tool for exploring shaking hazard from a physics-based perspective, its dependence on various physical parameters, and its correlation with other geological and seismological observables. Using this capability, we find some significant aspects of the shaking hazard can be anticipated by measures of the epicenters. In particular, asymmetries in the relative peak ground motion hazard along the faults appear well correlated with asymmetries in epicentral locations.Plate tectonics, Physicsbes11Lamont-Doherty Earth ObservatoryArticlesDynamic heterogeneities versus fixed heterogeneities in earthquake models
https://academiccommons.columbia.edu/catalog/ac:162505
Shaw, Bruce E.10.7916/D8ZS36JFTue, 27 Jun 2017 20:04:27 +0000A debate has raged over whether fixed material and geometrical heterogeneities, or alternatively dynamic stress heterogeneities, arising through frictional instabilities dominate earthquake complexity. It may also be that both types of heterogeneities interact and are important. This paper makes a first step in examining this interaction, combining two previously separate lines of research. One line examined friction, which has attractors (the subset of the phase space that the system evolves towards in the long run) on homogeneous faults, which are simple, and then added fixed heterogeneities to the faults to obtain complex attractors. Another line examined frictions, which produced complex attractors on homogeneous faults. Here, we examine frictions, which produce complex attractors on homogeneous faults, and study them on heterogeneous faults, in order to study the interaction of dynamic stress heterogeneities and fixed fault heterogeneities. We consider two types of fixed heterogeneities: an additive noise and a multiplicative noise to the frictional strength of the fault. Because of the linearity of the bulk elastodynamics, the attractor is unaffected by additive fixed noise in the strength of the fault: adding an arbitrary function of space, fixed in time, to the friction leaves the resulting attractor unchanged. In contrast, multiplicative fixed noise multiplying the friction can have a profound effect on the resulting attractor. In the small multiplicative noise amplitude limit, the frictional weakening attractor is little perturbed; at finite amplitudes, fixed heterogeneities substantially alter the attractor. We see, as one consequence, a shift toward longer length events at larger amplitudes. Fixed heterogeneities are seen to reduce the irregularities created by the frictional instability we study, but by no means destroy them. We quantify this by examining a measure of variability of the importance in hazard estimates, the coefficient of variation of large event recurrence times. The coefficient of variation is seen to remain substantial even for large fixed heterogeneities. For friction that weakens with time, so the underlying uniform fault attractor is simple, fixed heterogeneities increase irregularity. For all frictions examined, at low fixed heterogeneity the stress concentrations left over by the ends of the large events dominate where most of the small events occur, while at higher heterogeneity the stress irregularities left over by fixed fault heterogeneities begin to dominate where the small events occur. This may be the strongest signature of fixed heterogeneities, and should be examined further in the Earth. Finally, in what may have important implications for more sophisticated estimates of earthquake hazard, we see a correlation of locations with lower strength drop having higher variation in large event repeat times.Plate tectonics, Physicsbes11Lamont-Doherty Earth ObservatoryArticlesExistence of continuum complexity in the elastodynamics of repeated fault ruptures
https://academiccommons.columbia.edu/catalog/ac:162484
Shaw, Bruce E.; Rice, James R.10.7916/D8JT01FHTue, 27 Jun 2017 20:03:59 +0000What are the origins of earthquake complexity? The possibility that some aspects of the complexity displayed by earthquakes might be explained by stress heterogeneities developed through the self-organization of repeated ruptures has been suggested by some simple self-organizing models. The question of whether or not even these simple self-organizing models require at least some degree of material heterogeneity to maintain complex sequences of events has been the subject of some controversy. In one class of elastodynamic models, previous work has described complexity as arising on a model fault with completely uniform material properties. Questions were raised, however, regarding the role of discreteness, the relevance of the nucleation mechanism, and special parameter choices, in generating the complexity that has been reported. In this paper, we examine the question of whether or not continuum complexity is achieved under the stringent conditions of continuous loading, and whether the results are similar to previously claimed findings of continuum complexity or its absence. The elastodynamic model that we use consists of a 1-D fault boundary with friction, a steady slowly moving 1-D boundary parallel to the fault, and a 2-D scalar elastic media connecting the two boundaries. The constitutive law used involves a pair of sequential weakening processes, one occurring over a small slip (or velocity) and accomplishing a small fraction of the total strength drop, and the other at larger slip (or velocity) and providing the remaining strength drop. The large-scale process is motivated by a heat weakening instability. Our main results are as follows. (1) We generally find complexity of type I, a broad distribution of large event sizes with nonperiodic recurrence, when the modeled region is very long, along strike, compared to the layer thickness. (2) We find that complexity of type II, with numerous small events showing a power law distribution, is not a generic result but does definitely exist in a restricted range of parameter space. For that, in the slip weakening version of our model, the strength drop and nucleation size in the small slip process must be much smaller than in the large slip process, and the nucleation length associated with the latter must be comparable to layer thickness. This suggests a basis for reconciling different previously reported results. (3) Bulk dispersion appears to be relatively unimportant to the results. In particular, motions on the fault plane are seen to be relatively insensitive to a wide range of changes in the dispersion in the bulk away from the fault, both at long wavelengths and at short wavelengths. In contrast, the fault properties are seen to be very important to the results. (4) Nucleation from slip weakening and time-dependent weakening showed similar large-scale behavior. However, not all constitutive laws are insensitive to all nucleation approximations; those making a model “inherently discrete” and hence grid-dependent, in particular, can affect large scales. (5) While inherent discreteness has been seen to be a source of power law small-event complexity in some fault models, it does not appear to be the cause of the complexity in the attractors examined here, and reported in earlier work, fortuitously in the pecial parameter range, with the same class of continuum fault models and same or very similar constitutive relations. Continuum homogeneous dynamic complexity does indeed exist, although that includes type II small-event complexity only under restricted circumstances.Plate tectonics, Physicsbes11Lamont-Doherty Earth ObservatoryArticlesIntrinsic properties of a Burridge-Knopoff model of an earthquake fault
https://academiccommons.columbia.edu/catalog/ac:162401
Carlson, Jean M.; Langer, James S.; Shaw, Bruce E.; Tang, Chao10.7916/D84T6VBNTue, 27 Jun 2017 20:02:48 +0000We present a detailed numerical study of certain fundamental aspects of a one-dimensional homogeneous, deterministic Burridge-Knopoff model. The model is described by a massive wave equation, in which the key nonlinearity is associated with the stick-slip velocity-weakening friction force at the interface between tectonic plates. In this paper, we present results for the statistical distribution of slipping events in the limit of a very long fault and infinitesimally slow driving rates. Typically, we find that the magnitude distribution of smaller events is consistent with the Gutenberg-Richter law, while the larger events occur in excess of this distribution. The crossover from smaller to larger events is identified with a correlation length describing the transition from localized to delocalized events. We also find that there is a sharp upper cutoff describing the maximum large event. We identify how the correlation length and this upper cutoff scale with the parameters in the model. We find that both are independent of system size, while both do depend on the spatial discretization. In addition to the magnitude distribution, we present a series of measurements of other seismologically relevant quantities, including the event duration, the size of the rupture zone, and the energy release, and discuss the relationship between our measurements and the corresponding empirical laws in seismology.Physics, Plate tectonicsbes11Lamont-Doherty Earth ObservatoryArticlesUniversality in selection with local perturbations in the Saffman-Taylor problem
https://academiccommons.columbia.edu/catalog/ac:162398
Shaw, Bruce E.10.7916/D8TH8XPTTue, 27 Jun 2017 20:02:15 +0000An analytic theory using WKBJ methods for selection with local perturbations in the SaffmanTaylor [Proc. R. Soc. London, Ser. A 245, 312 (1958)] problem is presented. I obtain qualitative agreement with previously published phenomenology, including symmetric narrowed fingers for local reductions in the surface-tension parameter, narrowed asymmetric fingers for local increases,
and scaling of the tip curvature and asymmetry with the square root of the surface-tension parameter. The source of the universality in the perturbed problem is discussed, giving some explanation of why the experimental perturbations can be modeled by locally varying surface tension. Very good quantitative agreement between theory and a numerical simulation of the same perturbation is shown, with no adjustable parameters to fit. Finally, I outline experiments to test new behavior predicted by the theory; a quantitative prediction observable experimentally is given.Physicsbes11Lamont-Doherty Earth ObservatoryArticlesFinger narrowing under local perturbations in the Saffman-Taylor problem
https://academiccommons.columbia.edu/catalog/ac:162376
Zocchi, Giovanni; Shaw, Bruce E.; Libchaber, Albert; Kadanoff, Leo P.10.7916/D8280JKNTue, 27 Jun 2017 20:01:46 +0000We present an experimental study and a numerical simulation of the effect of time-independent, localized perturbations applied to the interface in the Saffman-Taylor fingering problem. When the perturbation is applied at a specific spot near the tip of the finger, the selection of the steady-state shape is drastically changed. In particular, one can obtain fingers with a width well below λ=1/2. A perturbation applied far away from the tip has no effect. We observe the same behavior in the simulation and in the experiment.Physicsbes11Lamont-Doherty Earth ObservatoryArticlesMeasurements of Anisotropic Ion Temperatures, Non-Thermal Velocities, and Doppler Shifts in a Coronal Hole
https://academiccommons.columbia.edu/catalog/ac:158038
Hahn, Michael; Savin, Daniel Wolf10.7916/D8JW8QQ3Tue, 27 Jun 2017 17:59:27 +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 (Ionized gases), Physics, Microphysicsmh2451, dws26Astronomy and AstrophysicsArticlesAstrochemistry in an Ion Storage Ring
https://academiccommons.columbia.edu/catalog/ac:158844
Novotny, Oldrich; Berg, M. H.; Buhr, H.; Froese, M.; Geppert, W.; Grieser, M.; Grussie, F.; Hamberg, M.; Krantz, C.; Lestinsky, M.; Mendes, M.; Nordhorn, C.; Novotny, S.; Orlov, D. A.; Petrignani, A.; Shornikov, A.; Stutzel, J.; Schwalm, D.; Savin, Daniel Wolf; Wolf, A.10.7916/D84X5JNMTue, 27 Jun 2017 17:57:26 +0000Storage ring studies of low energy electron collisions with molecular ions have been carried out for dissociative recombination (DR) of fluorine-bearing molecules. Here we report on work aiming to improve the understanding of astrochemistry involving HF, a possible spectroscopic tracer of interstellar H2. For CF+ the rate coefficient was obtained for temperatures down to 10 K. For D2F+ the DR fragmentation branching ratios were determined to be 66(3)%, 24(2)%, and 10(2)% for the F+D+D, DF+D, and D2+F channels, respectively. The molecular DR products of this reaction, DF and D2, display an unusually high level of internal excitation, close to their dissociation limit.Astrophysics, Plasma (Ionized gases), Physicson2138, dws26Astronomy and AstrophysicsReportsTheoretical electron-impact-ionization cross section for Fe11+ forming Fe12+
https://academiccommons.columbia.edu/catalog/ac:158077
Kwon, D. H.; Savin, Daniel Wolf10.7916/D82B97W2Tue, 27 Jun 2017 17:56:24 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesEvidence of Wave Damping at Low Heights in a Polar Coronal Hole
https://academiccommons.columbia.edu/catalog/ac:158023
Hahn, Michael; Landi, E.; Savin, Daniel Wolf10.7916/D8FJ2SMXTue, 27 Jun 2017 17:56:18 +0000We have measured the widths of spectral lines from a polar coronal hole using the Extreme Ultraviolet Imaging Spectrometer on board Hinode. Polar coronal holes are regions of open magnetic field and the source of the fast solar wind. We find that the line widths decrease at relatively low heights. Previous observations have attributed such decreases to systematic effects, but we find that such effects are too small to explain our results. We conclude that the line narrowing is real. The non-thermal line widths are believed to be proportional to the amplitude of Alfvén waves propagating along these open field lines. Our results suggest that Alfvén waves are damped at unexpectedly low heights in a polar coronal hole. We derive an estimate on the upper limit for the energy dissipated between 1.1 R ☉ and 1.3 R ☉ and find that it is enough to account for up to 70% of that required to heat the polar coronal hole and accelerate the solar wind.Astrophysics, Plasma (Ionized gases), Physicsmh2451, dws26Astronomy and AstrophysicsArticlesElectron-Ion Recombination of Mg6 + Forming Mg5 + and Of Mg7 + Forming Mg6 +: Laboratory Measurements and Theoretical Calculations
https://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 Wolf10.7916/D8ST80PFTue, 27 Jun 2017 17:56:17 +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 (Ionized gases), Physics, Microphysicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesElectron–Ion Recombination of Fe XII Forming Fe XI: Laboratory Measurements and Theoretical Calculations
https://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 Wolf10.7916/D8DJ5RGJTue, 27 Jun 2017 17:56:13 +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 (Ionized gases), Physics, Microphysicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesStorage-ring measurement of the hyperfine-induced 2s2p 3 P0→2s2 1 S0 transition rate in berylliumlike sulfur
https://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 Wolf10.7916/D88W3Q43Tue, 27 Jun 2017 17:56:05 +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 (Ionized gases), Physics, Microphysicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesAddendum: “Storage Ring Cross Section Measurements for Electron Impact Ionization of Fe11+ Forming Fe12+ and Fe13+” (2011, Apj, 729, 76)
https://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 Wolf10.7916/D8TT51TTTue, 27 Jun 2017 17:55:41 +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 (Ionized gases), Physics, Microphysicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesStorage Ring Cross-Section Measurements for Electron Impact Single and Double Ionization of Fe9 + and Single Ionization of Fe10 +
https://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 Wolf10.7916/D8ZK5SJ5Tue, 27 Jun 2017 17:55:38 +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 (Ionized gases), Physics, Microphysicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesAddendum: “Storage Ring Measurement of Electron Impact Ionization for Mg7+ Forming Mg8+” (2010, Apj, 712, 1166)
https://academiccommons.columbia.edu/catalog/ac:158029
Hahn, Michael; Bernhardt, D.; Lestinsky, M.; Muller, A.; Schippers, S.; Wolf, A.; Savin, Daniel Wolf10.7916/D8Q24948Tue, 27 Jun 2017 17:55:17 +0000Experimental cross-section data are presented as online data tables for electron impact single ionization of Mg7+ forming Mg8+.Astrophysics, Plasma (Ionized gases), Physics, Microphysicsmh2451, dws26Astronomy and AstrophysicsArticlesAddendum: “Storage Ring Cross-Section Measurements for Electron Impact Ionization of Fe12+ Forming Fe13+ and Fe14+” (2011, Apj, 735, 105)
https://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 Wolf10.7916/D8K93JDJTue, 27 Jun 2017 17:55:17 +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 (Ionized gases), Physics, Microphysicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesEffects of Configuration Interaction for Dielectronic Recombination of Na-like Ions Forming Mg-like Ions
https://academiccommons.columbia.edu/catalog/ac:157904
Kwon, D. H.; Savin, Daniel Wolf10.7916/D8TX3R6QTue, 27 Jun 2017 17:54:36 +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, Microphysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesDielectronic recombination of xenonlike tungsten ions
https://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 Wolf10.7916/D8Q530GPTue, 27 Jun 2017 17:54:36 +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 (Ionized gases), Physics, Microphysicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesFe15+ dielectronic recombination and the effects of configuration interaction between resonances with different captured electron principal quantum numbers
https://academiccommons.columbia.edu/catalog/ac:158735
Savin, Daniel Wolf; Kwon, D. H.10.7916/D8P84NR7Tue, 27 Jun 2017 17:54:36 +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, Microphysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesStorage Ring Cross Section Measurements for Electron Impact Ionization of Fe11+ Forming Fe12+ and Fe13+
https://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 Wolf10.7916/D8GQ77KSTue, 27 Jun 2017 17:54:18 +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, Microphysics, Plasma (Ionized gases), Physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesStorage Ring Cross Section Measurements for Electron Impact Ionization of Fe12 + Forming Fe13 + and Fe14 +
https://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 Wolf10.7916/D8BZ6GWHTue, 27 Jun 2017 17:54:18 +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, Microphysics, Plasma (Ionized gases), Physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesDifferential Emission Measure Analysis of a Polar Coronal Hole During the Solar Minimum in 2007
https://academiccommons.columbia.edu/catalog/ac:158020
Hahn, Michael; Landi, E.; Savin, Daniel Wolf10.7916/D8765R5HTue, 27 Jun 2017 17:54:18 +0000We have performed a differential emission measure (DEM) analysis for a polar coronal hole observed during solar minimum in 2007. Five observations are analyzed spanning the coronal hole from the central meridian to the boundary with the quiet-Sun corona. The observed heights ranged from 1.05 to 1.20 R ☉. The analysis shows that the plasma is not strictly isothermal anywhere, but rather has a high-temperature component that extends up to log T(K) = 6.2-6.3. The size and importance of this component depend on location, and its evolving magnitude with height marks the boundary between the coronal hole and the quiet corona, where it becomes dominant. The DEM of the coronal hole plasma below log T(K) = 6.0 decreases faster with height than that of the high-temperature component. We discuss the possible nature of the high-temperature component. Our results highlight the potential limitations of isothermal analyses. Such methods actually measure a DEM-weighted average temperature and as a result can infer artificial temperature gradients. Assuming the gas is isothermal along the line of sight can also yield incorrect electron densities. By revealing structures along the line of sight, a DEM analysis can also be used to more reliably interpret electron temperature and density measurements.Astrophysics, Plasma (Ionized gases), Physicsmh2451, dws26Astronomy and AstrophysicsArticlesA simple double-focusing electrostatic ion beam deflector
https://academiccommons.columbia.edu/catalog/ac:158723
Savin, Daniel Wolf; Kreckel, H.; Bruhns, H.; Miller, Kenneth; Davis, A.; Wahlin, E.; Hockh, S.10.7916/D86D63T9Tue, 27 Jun 2017 17:54:01 +0000We have developed an electrostatic, double-focusing 90° deflector for fast ion beams consisting of concentric cylindrical plates of differing heights. In contrast to standard cylindrical deflectors, our design allows for focusing of an incoming parallel beam not only in the plane of deflection but also in the orthogonal direction. The optical properties of our design resemble those of a spherical capacitor deflector while it is much easier and more cost effective to manufacture.Plasma (Ionized gases), Physics, Astrophysicsdws26, kam2211Astronomy and AstrophysicsArticlesA novel merged beams apparatus to study anion-neutral reactions
https://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.10.7916/D8B2854QTue, 27 Jun 2017 17:54:01 +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 (Ionized gases), Physics, Microphysicsdws26, kam2211Astronomy and AstrophysicsArticlesIs H+3 cooling ever important in primordial gas?
https://academiccommons.columbia.edu/catalog/ac:158047
Glover, S. C. O.; Savin, Daniel Wolf10.7916/D8BV7FXWTue, 27 Jun 2017 17:53:22 +0000Full tables of " Is H+3 cooling ever important in primordial gas?".Astrophysics, Plasma (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsData (information)Experimental rate coefficient for dielectronic recombination of neonlike iron forming sodiumlike iron
https://academiccommons.columbia.edu/catalog/ac:158840
Savin, Daniel Wolf; Schippers, S.; Schmidt, E. W.; Bernhardt, D.; Muller, A.; Lestinsky, M.; Hoffmann, J.; Orlov, D. A.; Wolf, A.; Lukic, D. V.10.7916/D8D227GCTue, 27 Jun 2017 17:53:22 +0000The rate coefficient for dielectronic recombination (DR) of Ne-like Fe16+ forming Na-like Fe15+ was measured employing the merged electron-ion beams technique at the heavy-ion storage-ring TSR of the Max-Planck-Institut für Kernphysik in Heidelberg, Germany. In the electron-ion collision energy range of 240–840 eV the merged-beams recombination rate coefficient is dominated by DR associated with 2s2 2p6 1S0 → 2s2 2p5 3d 1P1 core excitation. The experimental Fe16+ DR plasma rate coefficient is derived from the measured merged-beams rate coefficient. It is in good agreement with recent theoretical results.Astrophysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsReportsElectron-Ion Recombination of Fe X Forming Fe IX And of Fe XI Forming Fe X: Laboratory Measurements and Theoretical Calculations
https://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.10.7916/D8000BWTTue, 27 Jun 2017 17:53:02 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesA New Approach To Analyzing Solar Coronal Spectra And Updated Collisional Ionization Equilibrium Calculations. II. Updated Ionization Rate Coefficients
https://academiccommons.columbia.edu/catalog/ac:157841
Bryans, P.; Landi, E.; Savin, Daniel Wolf10.7916/D8RF64VGTue, 27 Jun 2017 17:52:37 +0000We have re-analyzed Solar Ultraviolet Measurement of Emitted Radiation (SUMER) observations of a parcel of coronal gas using new collisional ionization equilibrium (CIE) calculations. These improved CIE fractional abundances were calculated using state-of-the-art electron-ion recombination data for K-shell, L-shell, Na-like, and Mg-like ions of all elements from H through Zn and, additionally, Al- through Ar-like ions of Fe. They also incorporate the latest recommended electron impact ionization data for all ions of H through Zn. Improved CIE calculations based on these recombination and ionization data are presented here. We have also developed a new systematic method for determining the average emission measure (EM) and electron temperature (Te ) of an isothermal plasma. With our new CIE data and a new approach for determining average EM and Te , we have re-analyzed SUMER observations of the solar corona. We have compared our results with those of previous studies and found some significant differences for the derived EM and Te . We have also calculated the enhancement of coronal elemental abundances compared to their photospheric abundances, using the SUMER observations themselves to determine the abundance enhancement factor for each of the emitting elements. Our observationally derived first ionization potential factors are in reasonable agreement with the theoretical model of Laming.Astrophysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesElectron-ion recombination for Fe VIII forming Fe VII and Fe IX forming Fe VIII: measurements and theory
https://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.10.7916/D89G5XN7Tue, 27 Jun 2017 17:52:15 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesElectron-ion recombination of Si IV forming Si III: Storage-ring measurement and multiconfiguration Dirac-Fock calculations
https://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.10.7916/D8MW2T1QTue, 27 Jun 2017 17:51:54 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesLow-energy electron capture by Ne2+ ions from H(D)
https://academiccommons.columbia.edu/catalog/ac:158261
Savin, Daniel Wolf; Seredyuk, B.; Bruhns, H.; Seely, D. G.; Aliabadi, H.; Galutschek, E.; Havener, C. C.10.7916/D8H4229PTue, 27 Jun 2017 17:51:54 +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, Microphysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesElectron-ion recombination measurements of Fe7+, Fe8+, Fe13+ motivated by active galactic nuclei x-ray absorption features
https://academiccommons.columbia.edu/catalog/ac:158836
Savin, Daniel Wolf; Schippers, S.; Schmidt, E. W.; Bernhardt, D.; Brandau, C.; Muller, A.; Lestinsky, M.; Sprenger, F.; Hoffmann, J.; Orlov, D. A.; Grieser, M.; Repnow, R.; Wolf, A.; Lukic, D. V.; Schnell, M.10.7916/D8057RSTTue, 27 Jun 2017 17:51:53 +0000Recent spectroscopic models of active galactic nuclei have indicated that the recommended electron-ion recombination rate coefficients for iron ions with partially filled Mshells are incorrect in the temperature range where these ions form in photoionized plasmas. We have investigated this experimentally for Fe7+ forming Fe6+, Fe8+ forming Fe7+, and Fe13+ forming Fe12+. The recombination rate coefficient was measured employing the electron-ion merged beams method at the Heidelberg heavy-ion storage-ring TSR. The measured energy range encompassed at least all dielectronic recombination (DR) resonances associated with core excitations within the M-shell of the parent ions. Already in our first measurement, that is for Fe13+, we find unusually strong DR resonances at low electron-ion collision energies leading to low temperature plasma DR rate coefficients orders of magnitude larger than the recommended rate coefficientAstrophysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsReportsDielectronic Recombination of Fe XV Forming Fe XIV: Laboratory Measurements and Theoretical Calculations
https://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.10.7916/D8WD49F9Tue, 27 Jun 2017 17:51:53 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesCan Heavy Ion Storage Rings Contribute to Our Understanding of the Charge State Distributions in Cosmic Atomic Plasmas?
https://academiccommons.columbia.edu/catalog/ac:158732
Savin, Daniel Wolf10.7916/D8VD789XTue, 27 Jun 2017 17:51:52 +0000Interpreting cosmic spectra from ionized atomic gas hinges on our understanding the underlying physical processes which produce the observed spectra. Of particular importance are electron-ion recombination and electron impact ionization. These processes control the charge state distribution (CSD) of the gas. The CSD is intimately tied in to the observed spectral features and can also affect the thermal structure of the plasma. Heavy ion storage rings play a crucial role in improving our knowledge of electron-ion recombination and electron impact ionization, thereby deepening our understanding of the cosmos. Here we will review some of the astrophysical motivation behind laboratory astrophysics research with atomic ions at heavy ion storage rings. We also present some recent results, discuss some of the astrophysical implications, and present future astrophysical needs.Astrophysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsReportsDielectronic recombination data for dynamic finite-density plasmas II. The oxygen isoelectronic sequence
https://academiccommons.columbia.edu/catalog/ac:157835
Zatsarinny, O.; Gorczyca, T. W.; Korista, K. T.; Fu, J.; Badnell, N. R.; Mitthumsiri, W.; Savin, Daniel Wolf10.7916/D8H99G00Tue, 27 Jun 2017 17:51:10 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesCollisional Ionization Equilibrium for Optically Thin Plasmas. I. Updated Recombination Rate Coefficients for Bare through Sodium-like Ions
https://academiccommons.columbia.edu/catalog/ac:158086
Savin, Daniel Wolf; Bryans, P.; Badnell, N. R.; Gorczyca, T. W.; Laming, J. M.; Mitthumsiri, W.10.7916/D87S7ZK0Tue, 27 Jun 2017 17:51:10 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesImportance of Configuration Interaction for Accurate Atomic Data: Fluorescence Yields of K-Shell Vacancy, Lithium-Like Ions
https://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.10.7916/D8BK1P7STue, 27 Jun 2017 17:51:10 +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, Microphysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesStrong LSJ Dependence of Fluorescence Yields: Breakdown of the Configuration-average Approximation
https://academiccommons.columbia.edu/catalog/ac:157762
Savin, Daniel Wolf; Hasoǧlu, M. F.; Gorczyca, T. W.; Korista, K. T.; Manson, S. T.; Badnell, N. R.10.7916/D83205Q4Tue, 27 Jun 2017 17:51:10 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesDielectronic recombination data for dynamic finite-density plasmas IV. The carbon isoelectronic sequence
https://academiccommons.columbia.edu/catalog/ac:157813
Zatsarinny, O.; Gorczyca, T. W.; Korista, K. T.; Fu, J.; Badnell, N. R.; Savin, Daniel Wolf; Mitthumsiri, W.10.7916/D8N01HCFTue, 27 Jun 2017 17:51:00 +0000Mistakes in an earlier publication (Zatsarinny et al. 2004) have been discovered and are corrected. First, in Table 1, some of the DR fitting coefficients are incorrect due to initially undetected human errors in the postprocessing of the atomic data. As a result, we have refitted our archived totals for the entire sequence using up to seven terms in the summation of Eq. (3). We have retabulated in Table 1 only results for those ions that showed significant differences, which occur at lower temperatures, from those of our initial fitting procedure. We emphasize that these few errors were not in the atomic physics calculations, which are accurate for the entire sequence i.e. the adf09 files are unchanged, but rather only in the fitting algorithmAstrophysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesElectron capture by Ne4+ ions from atomic hydrogen
https://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.10.7916/D8J67SSJTue, 27 Jun 2017 17:50:48 +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, Microphysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesElectron capture by Ne3+ ions from atomic hydrogen
https://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.10.7916/D8QZ2MSQTue, 27 Jun 2017 17:50:25 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesDielectronic recombination data for dynamic finite-density plasmas
https://academiccommons.columbia.edu/catalog/ac:157810
Zatsarinny, O.; Gorczyca, T. W.; Korista, K. T.; Badnell, N. R.; Savin, Daniel Wolf10.7916/D8ZG732BTue, 27 Jun 2017 17:50:24 +0000Dielectronic recombination (DR) and radiative recombination (RR) data for carbon-like ions forming nitrogen-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 are presented and the results discussed for N+ to Zn24+, as well as Kr30+, Mo36+, Cd42+, and Xe48+. We find that the 2 → 2 (no change in the principal quantum number of the core electron) low-temperature DR does not scale smoothly with nuclear charge Z due to resonances straddling the ionization limit, thereby making explicit calculations for each ion necessary. The 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 (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesDielectronic recombination data for dynamic finite-density plasmas VII. The neon isoelectronic sequence
https://academiccommons.columbia.edu/catalog/ac:157817
Savin, Daniel Wolf; Zatsarinny, O.; Gorczyca, T. W.; Korista, K. T.; Badnell, N. R.10.7916/D8GF149XTue, 27 Jun 2017 17:50:24 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesDielectronic recombination data for dynamic finite-density plasmas II. The oxygen isoelectronic sequence
https://academiccommons.columbia.edu/catalog/ac:157838
Zatsarinny, O.; Gorczyca, T. W.; Korista, K. T.; Badnell, N. R.; Savin, Daniel Wolf10.7916/D8542ZDPTue, 27 Jun 2017 17:50:00 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesDielectronic Recombination of Fe XXI and Fe XXII via N = 2→N' = 2 Core Excitations
https://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.10.7916/D82B97VMTue, 27 Jun 2017 17:49:37 +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.Astrophysics, Plasma (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesElectron capture by Ne2+ ions from atomic hydrogen
https://academiccommons.columbia.edu/catalog/ac:158696
Savin, Daniel Wolf; Mroczkowski, T.; Rejoub, R.; Krstic, P. S.; Havener, C. C.10.7916/D8XP7FR6Tue, 27 Jun 2017 17:49:37 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesAssessment of the Fluorescence and Auger Database Used in Plasma Modeling
https://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.10.7916/D86400JFTue, 27 Jun 2017 17:49:36 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesShortcomings of the R-matrix method for treating dielectronic recombination
https://academiccommons.columbia.edu/catalog/ac:158705
Savin, Daniel Wolf; Gorczyca, T. W.; Badnell, N. R.10.7916/D81J9MKBTue, 27 Jun 2017 17:49:23 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesDielectronic Recombination (via N = 2 → N' = 2 Core Excitations) and Radiative Recombination of Fe XX: Laboratory Measurements and Theoretical Calculations
https://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.10.7916/D8WS941JTue, 27 Jun 2017 17:49:23 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesDielectronic Recombination of Fe XIX Forming Fe XVIII: Laboratory Measurements and Theoretical Calculations
https://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.10.7916/D8S18C94Tue, 27 Jun 2017 17:49:23 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesUncertainties in Dielectronic Recombination Rate Coefficients: Effects on Solar and Stellar Upper Atmosphere Abundance Determinations
https://academiccommons.columbia.edu/catalog/ac:158146
Savin, Daniel Wolf; Laming, J. M.10.7916/D8N87MMVTue, 27 Jun 2017 17:49:23 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesRate Coefficients for D(1s) + H+ ⇆ D+ + H(1s) Charge Transfer and Some Astrophysical Implications
https://academiccommons.columbia.edu/catalog/ac:158134
Savin, Daniel Wolf10.7916/D8HM5K8DTue, 27 Jun 2017 17:49:23 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesSimulating a Maxwellian plasma using an electron beam ion trap
https://academiccommons.columbia.edu/catalog/ac:158720
Savin, Daniel Wolf; Beiersdorfer, P.; Brown, G. V.; Kahn, S. M.; Beck, B. R.; Gu, M. F.; Liedahl, D. A.; Scofield, J. H.10.7916/D8MG809HTue, 27 Jun 2017 17:48:39 +0000We describe a technique for producing a Maxwell–Boltzmann electron energy distribution using an electron beam ion trap (EBIT). The technique was implemented on the Lawrence Livermore EBIT to simulate Maxwellian plasmas. We discuss technical and experimental issues related to these simulations. To verify the fidelity of the quasi-Maxwellian, we have measured line emission due to dielectronic recombination (DR) and electron impact excitation (EIE) of heliumlike neon, magnesium, and argon for a range of simulated electron temperatures. The ratio of DR to EIE lines in heliumlike ions is a well understood electron temperature diagnostic. The spectroscopically inferred quasi-Maxwellian temperatures are in excellent agreement with the simulated temperatures.Plasma (Ionized gases), Physics, Astrophysicsdws26Astronomy and AstrophysicsArticlesLaboratory Measurements of Fe XXIV Line Emission: 3→2 Transitions Near
Excitation Threshold
https://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.10.7916/D8MP5D3QTue, 27 Jun 2017 17:48:02 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesReevaluation of experiments and new theoretical calculations for electron-impact excitation of C3+
https://academiccommons.columbia.edu/catalog/ac:158693
Savin, Daniel Wolf; Janzen, P. H.; Gardner, L. D.; Reisenfeld, D. B.; Kohl, J. L.; Bartschat, K.10.7916/D8C53WP1Tue, 27 Jun 2017 17:48:02 +0000Experimental absolute-rate coefficients for electron-impact excitation of C3+ (2s2S1/2→2p2P1/2,3/2) near threshold [D. W. Savin, L. D. Gardner, D. B. Reisenfeld, A. R. Young, and J. L. Kohl, Phys. Rev. A 51, 2162 (1995)] have been reanalyzed to include a more accurate determination of optical efficiency and revised radiometric uncertainties which reduce the total systematic uncertainty of the results. Also, new R matrix with pseudostates (RMPS) calculations for this transition near threshold are presented. Comparison of the RMPS results to those of simpler close-coupling calculations indicates the importance of accounting for target continuum effects. The reanalyzed results of Savin et al. are in excellent agreement with the RMPS calculations; comparisons are also made to other measurements of this excitation. Agreement with the RMPS results is better for fluorescence technique measurements than for electron-energy-loss measurements.Astrophysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesImproved electron-beam ion-trap lifetime measurement of the Ne8+ 1s2s3S1 level
https://academiccommons.columbia.edu/catalog/ac:158681
Savin, Daniel Wolf; Trabert, E.; Beiersdorfer, P.; Brown, G. V.; Smith, A. J.; Utter, S. B.; Gu, M. F.10.7916/D8ZW1WRPTue, 27 Jun 2017 17:48:02 +0000An earlier electron-beam ion-trap (EBIT) lifetime measurement of the Ne8+ 1s2s3S1 level has been improved upon, reducing the uncertainties to less than the scatter in the existing theoretical calculations. The new result, 91.7±0.4 μs, agrees with the previous value, but is more precise by a factor of 4. The new value distinguishes among theoretical values, as agreement is obtained only with those calculations that employ "exact" nonrelativistic or relativistic wave functions. Routes to measurements with even higher accuracy are discussed.Astrophysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesDielectronic Recombination in Photoionized Gas. II. Laboratory Measurements for Fe XVIII and Fe XIX
https://academiccommons.columbia.edu/catalog/ac:157768
Savin, Daniel Wolf; Kahn, S. M.; Linkeman, J.; Saghiri, A. A.; Schmitt, M.; Grieser, M.; Repnow, R.; Schwalm, D.; Wolf, A.; Bartsch, T.; Brandau, C.; Hoffknecht, A.; Muller, A.; Schippers, S.; Chen, M. H.; Badnell, N. R.10.7916/D87D34ZPTue, 27 Jun 2017 17:48:02 +0000In photoionized gases with cosmic abundances, dielectronic recombination (DR) proceeds primarily via nlj → nl'j' core excitations (Δn = 0 DR). We have measured the resonance strengths and energies for Fe XVIII to Fe XVII and Fe XIX to Fe XVIII Δn = 0 DR. Using our measurements, we have calculated the Fe XVIII and Fe XIX Δn = 0 DR rate coefficients. Significant discrepancies exist between our inferred rates and those of published calculations. These calculations overestimate the DR rates by factors of ~2 or underestimate it by factors of ~2 to orders of magnitude, but none are in good agreement with our results. Almost all published DR rates for modeling cosmic plasmas are computed using the same theoretical techniques as the above-mentioned calculations. Hence, our measurements call into question all theoretical Δn = 0 DR rates used for ionization balance calculations of cosmic plasmas. At temperatures where the Fe XVIII and Fe XIX fractional abundances are predicted to peak in photoionized gases of cosmic abundances, the theoretical rates underestimate the Fe XVIII DR rate by a factor of ~2 and overestimate the Fe XIX DR rate by a factor of ~1.6. We have carried out new multiconfiguration Dirac-Fock and multiconfiguration Breit-Pauli calculations which agree with our measured resonance strengths and rate coefficients to within typically better than ≲30%. We provide a fit to our inferred rate coefficients for use in plasma modeling. Using our DR measurements, we infer a factor of ~2 error in the Fe XX through Fe XXIV Δn = 0 DR rates. We investigate the effects of this estimated error for the well-known thermal instability of photoionized gas. We find that errors in these rates cannot remove the instability, but they do dramatically affect the range in parameter space over which it forms.Astrophysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesAbsolute cross section for Si2+(3s21S→3s3p1P) electron-impact excitation
https://academiccommons.columbia.edu/catalog/ac:158678
Savin, Daniel Wolf; Reisenfeld, D. B.; Gardner, L. D.; Janzen, P. H.; Kohl, J. L.10.7916/D83N2D6XTue, 27 Jun 2017 17:48:00 +0000We have measured the absolute cross section for electron-impact excitation (EIE) of Si2+(3s21S→3s3p1P) from energies below threshold to 11 eV above. A beams modulation technique with inclined electron and ion beams was used. Radiation at 120.7 nm from the excited ions was detected using an absolutely calibrated optical system. The fractional population of the Si2+(3s3p3Po) metastable state in the incident ion beam was determined to be 0.210±0.018 (1.65σ). The data have been corrected for contributions to the signal from radiative decay following excitation from the metastable state to 3s3p1P and 3p23P, and excitation from the ground state to levels above the 3s3p1P level. The experimental 0.56±0.08-eV energy spread allowed us to resolve complex resonance structure throughout the studied energy range. At the reported ±14% total experimental uncertainty level (1.65σ), the measured structure and absolute scale of the cross section are in good agreement with 12-state close-coupling R-matrix calculations.Astrophysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesExperimentally Derived Dielectronic Recombination Rate Coefficients For Helium-Like C V and Hydrogenic O VIII
https://academiccommons.columbia.edu/catalog/ac:157774
Savin, Daniel Wolf10.7916/D8V69VCJTue, 27 Jun 2017 17:48:00 +0000Using published measurements of dielectronic recombination (DR) resonance strengths and energies for C V to C IV and O VIII to O VII, we have calculated the DR rate coefficient for these ions. Our derived rates are in good agreement with multiconfiguration, intermediate-coupling and multiconfiguration, fully relativistic calculations, as well as with most LS-coupling calculations. Our results are not in agreement with the recommended DR rates commonly used for modeling cosmic plasmas. We have used theoretical radiative recombination (RR) rates in conjunction with our derived DR rates to produce a total recombination rate for comparison with unified RR + DR calculations in LS coupling. Our results are not in agreement with undamped, unified calculations for C V but are in reasonable agreement with damped, unified calculations for O VIII. For C V, the Burgess general formula (GF) yields a rate that is in very poor agreement with our derived rate. The Burgess and Tworkowski modification of the GF yields a rate that is also in poor agreement. The Merts et al. modification of the GF yields a rate that is in fair agreement. For O VIII, the GF yields a rate that is in fair agreement with our derived rate. The Burgess and Tworkowski modification of the GF yields a rate that is in good agreement, and the Merts et al. modification yields a rate that is in very poor agreement. These results suggest that for ΔN = 1 DR, it is not possible to know a priori which formula will yield a rate closer to the true DR rate. We describe the technique used to obtain DR rate coefficients from laboratory measurements of DR resonance strengths and energies. For use in plasma modeling, we also present easy-to-use fitting formulae for the experimentally derived DR rates.Astrophysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesDielectronic recombination for boronlike ions
https://academiccommons.columbia.edu/catalog/ac:158690
Savin, Daniel Wolf; Chen, M. H.; Reed, K. J.; Guo, D. S.10.7916/D8HX1PGXTue, 27 Jun 2017 17:47:42 +0000We have calculated the total dielectronic recombination (DR) coefficients for the 2P1/2 and 2P3/2 states in B-like Ti17+, Fe21+, and Mo37+ ions for electron temperatures 0.1<~T<~10000 eV. The calculations are carried out using the multiconfiguration Dirac-Fock method in intermediate coupling with a configuration interaction. We find that accurate Coster-Kronig energies are critical for a successful determination of low-temperature DR coefficients. We also find that the DR involving fine-structure excitations can be as important as the 2s-2p excitation channels in the low-temperature regime for some ions.Astrophysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesA high-resolution transmission-type x-ray spectrometer designed for observation of the Kα transitions of highly charged high-Z ions
https://academiccommons.columbia.edu/catalog/ac:158717
Savin, Daniel Wolf; Widmann, K.; Beiersdorfer, P.; Brown, G. V.; Lopez-Urrutia, J. R. Crespo; Decaux, V.10.7916/D8JT0188Tue, 27 Jun 2017 17:47:40 +0000High-resolution reflection-type crystal spectrometers have been used for x-ray energies up to 13 keV, e.g., the K-shell radiation of heliumlike Kr. In order to extend crystal spectrometer measurements to higher energy x rays from higher-Z elements, we employ the crystal in transmission. The geometry we use is known as DuMond geometry. Using such a transmission-type crystal x-ray spectrometer, we have measured the K-shell radiation of various highly charged high-Z ions. In particular, we present a measurement of the 1s2p 1P1→1s2 1S0 transition in heliumlike xenon, Xe52+. For this transition, we measure a linewidth of 34 eV, which demonstrates that the resolving power we achieved with the new spectrometer is on the order of 1000Plasma (Ionized gases), Physics, Astrophysicsdws26Astronomy and AstrophysicsArticlesPrecision measurement of the lifetime of the 1s2s3S1 metastable level in heliumlike O6+
https://academiccommons.columbia.edu/catalog/ac:158672
Savin, Daniel Wolf; Lopez-Urrutia, J. R. Crespo; Beiersdorfer, P.; Widmann, K.10.7916/D88D063GTue, 27 Jun 2017 17:47:38 +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, Microphysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesLaboratory Measurements of Fe XXIV L-Shell Line Emission
https://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.10.7916/D8BC48B7Tue, 27 Jun 2017 17:47:21 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesDirect Observation of the Spontaneous Emission of the Hyperfine Transition F = 4 to F = 3 in Ground State Hydrogenlike 165Ho66+ in an Electron Beam Ion Trap
https://academiccommons.columbia.edu/catalog/ac:158708
Savin, Daniel Wolf; Lopez-Urrutia, Jose R. Crespo; Beiersdorfer, P.; Widmann, Klaus10.7916/D82V2RZPTue, 27 Jun 2017 17:47:13 +0000We report the first direct laboratory measurement of the spontaneous emission due to the hyperfine splitting of the ground state of a highly charged hydrogenlike ion excited by electron collisions. The transition between the F = 4 and F = 3 levels of the 1s2S1/2 configuration of hydrogenlike 165Ho65+ was observed and its wavelength was determined to 5726.4±1.5Å. After taking into account relativistic, nuclear charge distribution, Bohr-Weisskopf, and QED corrections, we observe a significant deviation from commonly tabulated values of the nuclear dipole magnetic moment of this nucleusAstrophysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesDielectronic Recombination in Photoionized Gas: The Importance of Fine-structure Core Excitations
https://academiccommons.columbia.edu/catalog/ac:157801
Savin, Daniel Wolf; Bartsch, T.; Chen, M. H.; Kahn, S. M.; Liedahl, D. A.; Linkemann, J.; Muller, A.; Schippers, S.; Schmitt, M.; Schwalm, D.; Wolf, A.10.7916/D89C7779Tue, 27 Jun 2017 17:46:53 +0000At the low electron temperatures existing in photoionized gases with cosmic abundances, dielectronic recombination (DR) proceeds primarily via nlj→nl`j` excitations of core electrons (Δn=0 DR). At these temperatures, the dominant DR channel often involves 2p1/2→2p3/2 fine-structure core excitations, which are not included in LS-coupling calculations or the Burgess formula. Using the heavy-ion storage ring at the Max-Planck-Institut für Kernphysik in Heidelberg, Germany, we have verified experimentally for Fe XVIII that DR proceeding via this channel can be significant in relation to other recombination rates, especially at the low temperatures characteristic of photoionized gases. At temperatures in photoionized gases near where Fe XVIII peaks in fractional abundance, our measured Fe XVIII to Fe XVII Δn=0 DR rate coefficient is a factor of ~2 larger than predicted by existing theoretical calculations. We provide a fit to our measured rate coefficient for ionization equilibrium models. We have carried out new fully relativistic calculations using intermediate coupling, which include the 2p1/2→2p3/2 channel and agree to within ~30% with our measurements. DR via the 2p1/2→2p3/2 channel may also have spectroscopic implications, providing unique spectral signatures at soft X-ray wavelengths that could provide good electron temperature diagnostics.Astrophysics, Plasma (Ionized gases), Physicsdws26Astronomy and AstrophysicsArticlesLaboratory Measurements of Fe XXIV L-Shell Line Emission
https://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.10.7916/D8G169N7Tue, 27 Jun 2017 17:46:43 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesAbsolute measurement of dielectronic recombination for C3+ in a known external field
https://academiccommons.columbia.edu/catalog/ac:158056
Gardner, L. D.; Reisenfeld, D. B.; Young, A. R.; Kohl, J. L.; Savin, Daniel Wolf10.7916/D8KS72B6Tue, 27 Jun 2017 17:46:35 +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 (Ionized gases), Physics, Microphysicsdws26Astronomy and AstrophysicsArticlesIn situ absolute calibration of a channel electron multiplier for detection of positive ions
https://academiccommons.columbia.edu/catalog/ac:158714
Savin, Daniel Wolf; Gardner, L. D.; Reisenfeld, D. B.; Young, A. R.; Kohl, J. L.10.7916/D81263GTTue, 27 Jun 2017 17:46:35 +0000A technique has been developed to determine the absolute single particle counting efficiency of a channel electron multiplier (CEM) for positively charged ions at keV energies. The calibration technique is applicable to positive ion detectors in general. Ion beam currents of C2+ were created by charge transfer of C3+ on H2 in the thin target regime. By adjusting the H2 pressure in the beam scattering chamber from 10−10 to 10−6 Torr, C2+ currents could be created either low enough to be detected by the CEM in the particle counting mode or high enough to be measured as a current using the CEM as a Faraday cup. The CEM counting efficiency was determined by comparing the C2+ count rate to the C2+ current, scaling by the change in H2 pressure, and also scaling by the incident C3+ current for each C2+ measurement. This method, which effectively uses the charge transfer cross section as a ‘‘transfer standard,’’ allows the CEM counting efficiency to be determined in situ and to be monitored accurately over extended periods of time. The calibration requires that only the relative, not the absolute, pressure change be known. The technique does not require the value of the charge transfer cross section to be known. The accuracy of the calibration technique for the present results was 10% at a confidence level considered to be equivalent to a statistical 90% confidence level. For the present work, the peak counting efficiency of a Galileo 4039 CEM for 32.5 keV C2+ ions was determined to be 96%.Plasma (Ionized gases), Physics, Astrophysicsdws26Astronomy and AstrophysicsArticles