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Spectral catalogue of the intermediate ionization states of iron in the extreme ultraviolet

Description: Using precisely controlled laboratory conditions we have begun to establish a spectral catalogue of the intermediate ionization states of iron, Fe IX - Fe XXIV, in the extreme ultraviolet. The measurements are being performed in support of the development of reliable modeling codes for the analysis of data from the Extreme Ultraviolet Explorer and future space astrophysics missions sensitive to extreme ultraviolet radiation. They aim to resolve the controversies surrounding the short-wavelength spectra of stellar coronae. Preliminary measurements showing the wealth of iron lines in the 50-120 {Angstrom} region are presented.
Date: May 13, 1998
Creator: Beiersdorfer, P.; Utter, S. B. & Brown, G. V.
Partner: UNT Libraries Government Documents Department

Polarization measurements of the Lyman-(alpha)1 x-ray emission lines of hydrogenlike Ar17+ and Fe25+ at high electron impact energies

Description: We have measured the polarization of the 2p{sub 3/2} {yields} 1s{sub 1/2} Lyman-{alpha}{sub 1} x-ray line of hydrogenlike Ar{sup 17+} and Fe{sup 25+} at electron impact energies ranging from 7 to 25 threshold units. The highly charged argon and iron ions were produced using the Lawrence Livermore National Laboratory SuperEBIT electron beam ion trap. A combination of two crystal spectrometers and a microcalorimeter were used to record the Lyman-{alpha} x-ray emission of Ar{sup 17+} and Fe{sup 25+} and to infer the polarization of the Lyman-{alpha}{sub 1} line. Our results show a systematic discrepancy with the predictions of distorted-wave calculations.
Date: January 29, 2006
Creator: Robbins, D. L.; Beiersdorfer, P.; Faenov, A. Y.; Pikuz, T. A.; Thorn, D. B.; Chen, H. et al.
Partner: UNT Libraries Government Documents Department

Spectropolarimetry of FIRST 0840 + 3633

Description: We present Keck spectropolarimetry of a rare ``Iron Lo- BALQSO,`` FIRST 0840+3633. The continuum is {approximately}4% polarized near 2000{Angstrom} rest-frame, but falls to {approximately}2% at longer wavelengths, and maintains a relatively constant position angle of 50{degrees}. The emission lines are unpolarized. The polarization increases up to {approximately}8% in the low-ionization absorption troughs of Mg II {lambda}2800 and Al III {lambda}1860. The polarization and its position angle vary in a complicated manner across the metastable Fe II absorption lines, suggesting that more than one mechanism is at work or that the system geometry is complex.
Date: February 1, 1997
Creator: Brotherton, M.S.; Van Breugel, N.; Dey, A. & Antonucci, R.
Partner: UNT Libraries Government Documents Department

Capella Corona Revisited: a Combined View from Textit XMM-Newton RGS, Textit Chandra HETGS, and LETGS

Description: We present a combined analysis of the X-ray emission of the Capella corona obtained with XMM-Newton RGS, Chandra HETGS, and LETGS. An improved atomic line database and a new differential emission measure (DEM) deconvolution method are developed for this purpose. Our new atomic database is based on the Astrophysical Plasma Emission Database and incorporates improved calculations of ionization equilibrium and line emissivities for L-shell ions of abundant elements using the Flexible Atomic Code. The new DEM deconvolution method uses a Markov Chain Monte-Carlo (MCMC) technique which differs from existing MCMC or {chi}{sup 2}-fitting based methods. We analyze the advantages and disadvantages of each individual instrument in determining the DEM and elemental abundances. We conclude that results from either RGS or HETGS data alone are not robust enough due to their failure to constrain DEM in some temperature region or the lack of significant continuum emission in the wavelength band of the spectrometers, and that the combination of HETGS and RGS gives more stringent constraints on the DEM and abundance determinations. Using the LETGS data, we show that the recently discovered inconsistencies between the EUV and X-ray lines of Fe XVIII and XIX also exist in more highly charged iron ions, up to Fe XXIII, and that enhanced interstellar absorption due to partially ionized plasma along the Capella line of sight may explain some, but not all, of these discrepancies.
Date: June 19, 2006
Creator: Gu, Ming Feng; Gupta, R.; Peterson, J.R.; Sako, M.; Kahn, S.M. & /Stanford U., Phys. Dept. /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

Lack of Bystander Effects From High LET Radiation For Early Cytogenetic Endpoints.

Description: The aim of this work was to study radiation-induced bystander effects for early cytogenetic end points in various cell lines using the medium transfer technique after exposure to high- and low-LET radiation. Cells were exposed to 20 MeV/ nucleon nitrogen ions, 968 MeV/nucleon iron ions, or 575 MeV/nucleon iron ions followed by transfer of the conditioned medium from the irradiated cells to unirradiated test cells. The effects studied included DNA double-strand break induction, {gamma}-H2AX focus formation, induction of chromatid breaks in prematurely condensed chromosomes, and micronucleus formation using DNA repair-proficient and -deficient hamster and human cell lines (xrs6, V79, SW48, MO59K and MO59J). Cell survival was also measured in SW48 bystander cells using X rays. Although it was occasionally possible to detect an increase in chromatid break levels using nitrogen ions and to see a higher number of {gamma}-H2AX foci using nitrogen and iron ions in xrs6 bystander cells in single experiments, the results were not reproducible. After we pooled all the data, we could not verify a significant bystander effect for any of these end points. Also, we did not detect a significant bystander effect for DSB induction or micronucleus formation in these cell lines or for clonogenic survival in SW48 cells. The data suggest that DNA damage and cytogenetic changes are not induced in bystander cells. In contrast, data in the literature show pronounced bystander effects in a variety of cell lines, including clonogenic survival in SW48 cells and induction of chromatid breaks and micronuclei in hamster cells. To reconcile these conflicting data, it is possible that the epigenetic status of the specific cell line or the precise culture conditions and medium supplements, such as serum, may be critical for inducing bystander effects.
Date: May 7, 2008
Creator: Groesser, Torsten; Cooper, Brian & Rydberg, Bjorn
Partner: UNT Libraries Government Documents Department

Homologous recombination contributes to the repair of DNA double-strand breaks induced by high-energy iron ions

Description: To test the contribution of homologous recombinational repair (HRR) in repairing DNA damaged sites induced by high-energy iron ions, we used: (1) HRR-deficient rodent cells carrying a deletion in the RAD51D gene and (2) syngeneic human cells impaired for HRR by RAD51D or RAD51 knockdown using RNA interference. We show that in response to iron ions, HRR contributes to cell survival in rodent cells, and that HRR-deficiency abrogates RAD51 foci formation. Complementation of the HRR defect by human RAD51D rescues both enhanced cytotoxicity and RAD51 foci formation. For human cells irradiated with iron ions, cell survival is decreased, and, in p53 mutant cells, the levels of mutagenesis are increased when HRR is impaired. Human cells synchronized in S phase exhibit more pronounced resistance to iron ions as compared with cells in G1 phase, and this increase in radioresistance is diminished by RAD51 knockdown. These results implicate a role for RAD51-mediated DNA repair (i.e. HRR) in removing a fraction of clustered lesions induced by charged particle irradiation. Our results are the first to directly show the requirement for an intact HRR pathway in human cells in ensuring DNA repair and cell survival in response to high-energy high LET radiation.
Date: June 29, 2010
Creator: Zafar, Faria; Seidler, Sara B.; Kronenberg, Amy; Schild, David & Wiese, Claudia
Partner: UNT Libraries Government Documents Department

Investigation of Mn Implanted LiNbO{sub 3} applying electron paramagnetic resonance technique

Description: The effect of ion implantation on the LiNbO{sub 3} crystal is studied using electron paramagnetic resonance spectroscopy (EPR). EPR measurements on these crystals were performed as a function of ion species Mn and Fe and fluence at room temperature. Also the effect of the laser illumination on the EPR signal was determined by illuminating the crystal in situ and measuring the decay and growth of the EPR signal. LiNbO{sub 3}:Mn{sup 2+} at a depth of approximately 200 nm was formed by implantation of 2.5 {times} 10{sup 14} Mncm{sup 2} and 1 {times} 10{sup 17} Mn/cm{sup 2} at 2 MeV. The implanted samples were compared with bulk doped crystals. It was found that the decay and growth of Mn EPR for the implanted crystal is very small compared with the bulk doped LiNbO{sub 3}:Mn crystal. This was found to be primarily due to the spin concentration on the crystals. On the other, hand the decay time of the high fluence is about 40% slower than the decay of the low fluence implanted crystal.
Date: October 1, 1997
Creator: Darwish, A.; Ila, D.; Poker, D.B. & Hensley, D.K.
Partner: UNT Libraries Government Documents Department

Laboratory x-ray spectroscopy experiments in support of NASA`s x-ray satellite missions

Description: With support from NASA, we are performing a series of laboratory astrophysics investigations designed to address fundamental uncertainties in basic atomic physics processes relevant to the interpretation of discrete X-ray spectra of cosmic plasmas. Moderate resolution spectra acquired by the ASCA Observatory already demonstrate the inadequacy of currently available spectral modelling codes for this wavelength band. With the upcoming launches of AXAF, XMM, ASTRO E, and Spektrum Roentgen-Gamma, the demand for significant advances in this field will increase dramatically. Our program is based on the exploitation of the Electron Beam Ion Trap facility at the Lawrence Livermore National Laboratory, and a unique set of spectrometers and experimental techiques specifically developed for this purpose. Recent experiments have been devoted to definitive measurements of line emissivities for iron L-shell ions in optically thin, collisional plasmas.
Date: May 22, 1998
Creator: Kahn, S. M., Columbia University
Partner: UNT Libraries Government Documents Department

Effect of irradiation spectrum on the microstructure of ion-irradiated Al{sub 2}O{sub 3}

Description: Polycrystalline samples of alpha-alumina have been irradiated with various ions ranging from 3.6 MeV Fe{sup +} to 1 MeV H{sup +} ions at 650 C. Cross-section transmission electron microscopy was used to investigate the depth-dependent microstructure of the irradiated specimens. The microstructure following irradiation was observed to be dependent on the irradiation spectrum. In particular, defect cluster nucleation was effectively suppressed in specimens irradiated with light ions such as 1 MeV H{sup +} ions. On the other hand, light ion irradiation tended to accelerate the growth rate of dislocation loops. The microstructural observations are discussed in terms of ionization enhanced diffusion processes.
Date: December 31, 1994
Creator: Zinkle, S.J.
Partner: UNT Libraries Government Documents Department

Strong directional out-of-plane scattering in multiple ionizing highly charged ion-atom collisions

Description: The azimuthal ({phi}{sub r}) and polar angle ({theta}{sub r}) scattering of projectiles in coincidence with recoil ions has been studied for 0.53 MeV/u F{sup 8+} + Ne. For high degree of ionization of the target we find the resultant transverse momentum of all electrons emitted into the continuum to increase with the number of ejected electrons and to have a direction mostly not co-planar with the scattering plane.
Date: December 31, 1990
Creator: Gonzalez, A.; Hagmann, S.; Quinteros, T.; Kraessig, B.; Koch, R.; Schmidt-Boecking, H. et al.
Partner: UNT Libraries Government Documents Department

Persistence of gamma-H2AX and 53BP1 foci in proliferating and nonproliferating human mammary epithelial cells after exposure to gamma-rays or iron ions

Description: To investigate {gamma}-H2AX (phosphorylated histone H2AX) and 53BP1 (tumour protein 53 binding protein No. 1) foci formation and removal in proliferating and non-proliferating human mammary epithelial cells (HMEC) after exposure to sparsely and densely ionizing radiation under different cell culture conditions. HMEC cells were grown either as monolayers (2D) or in extracellular matrix to allow the formation of acinar structures in vitro (3D). Foci numbers were quantified by image analysis at various time points after exposure. Our results reveal that in non-proliferating cells under 2D and 3D cell culture conditions, iron-ion induced {gamma}-H2AX foci were still present at 72 h after exposure, although 53BP1 foci returned to control levels at 48 h. In contrast in proliferating HMEC, both {gamma}-H2AX and 53BP1 foci decreased to control levels during the 24-48 h time interval after irradiation under 2D conditions. Foci numbers decreased faster after {gamma}-ray irradiation and returned to control levels by 12 h regardless of marker, cell proliferation status, and cell culture condition. Conclusions: The disappearance of radiation induced {gamma}-H2AX and 53BP1 foci in HMEC have different dynamics that depend on radiation quality and proliferation status. Notably, the general patterns do not depend on the cell culture condition (2D versus 3D). We speculate that the persistent {gamma}-H2AX foci in iron-ion irradiated non-proliferating cells could be due to limited availability of double strand break (DSB) repair pathways in G0/G1-phase, or that repair of complex DSB requires replication or chromatin remodeling.
Date: December 22, 2010
Creator: Groesser, Torsten; Chang, Hang; Fontenay, Gerald; Chen, James; Costes, Sylvain V.; Barcellos-Hoff, Mary Helen et al.
Partner: UNT Libraries Government Documents Department

Optical and magnetic properties of silica implanted with N{sup +} and Fe{sup +}

Description: Silica platelets (Corning 7940) were implanted sequentially with N{sup +} at 52 keV to different doses ranging from 0 to 1.2{times}10{sup 17} ions cm{sup {minus}2} and then with Fe{sup +} at 160 keV to a dose of 6{times}l0{sup 16} ions cm{sup {minus}2}. The optical absorption decreased with increasing N{sup +} dose at photon energies ranging from 1.4 to 6.5 eV. The relative intensity, S(0{degrees}), of the ferromagnetic resonance absorption and its resonance field, H{sub s}(0{degrees}), at {theta}=0{degrees} were larger than S(90{degrees}) and H{sub s}(90{degrees}), at {theta}=0{degrees}, where {theta} is the angle between the applied magnetic field and the normal to the implanted surface. The maximum values of S(0{degrees}) and S(90{degrees}) were observed near the N/Fe atomic ratio of 0.2. At the similar atomic ratio, the differential relative intensity, S(0{degrees}){minus} S(90{degrees}), and the differential resonance field, H{sub s}(0{degrees}){minus} H{sub s}(90{degrees}), associated with the degree of magnetic interaction between the produced compounds, also showed maxima. We conclude that sequential ion-implantation of N{sup +} and Fe{sup +} into silica causes a chemical interaction to produce iron nitrides.
Date: December 1, 1995
Creator: Isobe, T.; Weeks, R.A. & Zuhr, R.A.
Partner: UNT Libraries Government Documents Department

Analytical electron microscopy of precipitates in ion-implanted MgAl{sub 2}O{sub 4} spinel

Description: Magnesium aluminate spinel (MgAl{sub 2}O{sub 4}) is being considered as an insulator material within proposed fusion reactors where considerable radiation fields are anticipated. Analytical electron microscopy (AEM) has been used to investigate precipitates within MgAl{sub 2}O{sub 4} spinel following implantation of Al{sup +}, Mg{sup +}, or Fe{sup 2+} ions. Combined diffraction experiments, energy dispersive X-ray spectrometry (EDS), electron energy-loss spectrometry (EELS), and energy-filtered imaging were employed to identify and characterize precipitates observed in the implanted ion region. Diffraction studies suggested these are metallic aluminum colloids, although EELS and energy-filtered images revealed this to be the case only for the Al{sup +} and Mg{sup +} implantations, and not for Fe{sup 2+} ion implantations. Multiple-least-squares (MLS) fitting of EELS spectra was employed to quantify the volume fraction of metallic aluminum when present in the implanted ion region. Energy-filtered images of the implanted ion region clearly show the colloid distribution in the Al{sup +} and Mg{sup +} implanted spinel. Energy-filtered images from the Fe {sup 2+} ion implanted spinel indicate that the features visible in diffraction contrast cannot be associated with either metallic aluminum or iron-rich precipitates.
Date: 1994
Creator: Evans, N. D.; Zinkle, S. J. & Bentley, J.
Partner: UNT Libraries Government Documents Department

XUV and X-ray spectra from Texas Experimental Tokamak plasmas

Description: The first XUV and x-ray spectra were recorded from TEXT with a grazing-incidence grating spectrograph and new crystal spectrographs. Time- and space-integrated data yielded a qualitative description of the plasma. Line radiation from O, Cr, Fe, and Ni ions was recorded and identified with the aid of ab initio atomic structure calculations. Approximate values of plasma characteristics were obtained from the spectra. A derived electron temperature of 800 eV and electron density of 2 {times} 10{sup 13} cm{sup {minus}3} are consistent with results from other diagnostics. Spectrometers which will provide time- and space-resolved data are being designed for quantitative rate and transport studies.
Date: May 28, 1982
Creator: Bleach, R.D.; Burkhalter, P.G.; Nagel, D.J. & Rowan, W.
Partner: UNT Libraries Government Documents Department

Triple ion-beam studies of radiation damage in 9Cr2WVTa ferritic/martensitic steel

Description: To simulate radiation damage under a future Spallation Neutron Source (SNS) environment, irradiation experiments were conducted on a candidate 9Cr-2WVTa ferritic/martensitic steel using the Triple Ion Facility (TIF) at ORNL. Irradiation was conducted in single, dual, and triple ion beam modes using 3.5 MeV Fe{sup ++}, 360 keV He{sup +}, and 180 keV H{sup +} at 80, 200, and 350{degrees}C. These irradiations produced various defects comprising black dots, dislocation loops, line dislocations, and gas bubbles, which led to hardening. The largest increase in hardness, over 63 %, was observed after 50 dpa for triple beam irradiation conditions, revealing that both He and H are augmenting the hardening. Hardness increased less than 30 % after 30 dpa at 200{degrees}C by triple beams, compatible with neutron irradiation data from previous work which showed about a 30 % increase in yield strength after 27.2 dpa at 365{degrees}C. However, the very large concentrations of gas bubbles in the matrix and on lath and grain boundaries after these simulated SNS irradiations make predictions of fracture behavior from fission reactor irradiations to spallation target conditions inadvisable.
Date: November 1, 1997
Creator: Lee, E.H.; Hunn, J.D.; Rao, G.R.; Klueh, R.L. & Mansur, L.K.
Partner: UNT Libraries Government Documents Department

Laboratory astrophysics: Measurements of n = n{prime} to n = 2 line emission in Fe{sup 16+} to Fe{sup 23+}

Description: One of the dominant forms of astronomical line emission in the 6 {angstrom} to 18 {angstrom} spectral region is line emission produced by n = n{prime} to n = 2 transitions in Fe{sup 16+} to Fe{sup 23+} (i.e., Fe L-shell n-2 line emission). Using the Lawrence Livermore National Laboratory electron beam ion trap (EBIT) facility, the authors have carried out a number of measurements designed to address astrophysical issues concerning Fe L-shell line emission. Desired ions are produced and trapped using the nearly monoenergetic electron beam of EBIT. Trapped ions are collisionally excited and the resulting X-ray line emission detected using Bragg crystal spectrometers. They have recently completed a line survey of Fe L-shell 3-2 line emission. The line survey will allow a more reliable accounting of line blending in astronomical spectra. They have now begun a series of broadband, high resolution line ratio measurements. These measurements are designed to benchmark atomic calculations used in astronomical plasma emission codes and also for comparison with X-ray spectral observations of astronomical objects. Initial measurements have been carried out in Fe{sup 23+}. Preliminary results agree with distorted wave calculations to within 20% and better.
Date: March 5, 1996
Creator: Savin, D.W.; Beiersdorfer, P.; Lopez-Urrutia, J.C.; Decaux, V.; Liedahl, D.A.; Reed, K.J. et al.
Partner: UNT Libraries Government Documents Department

SUBSTITUTED IRON OXIDES FOR THE GRANT ENTITLED LASER PROCESSING OF ADVANCED MAGNETIC MATERIALS

Description: Structural and morphological characteristics of (1-x){alpha}-Fe{sub 2}O{sub 3}-xSnO{sub 2} (x = 0.0-1.0) nanoparticles obtained under hydrothermal conditions have been investigated by X-ray diffraction (XRD), transmission Moessbauer spectroscopy, scanning (SEM) and transmission electron microscopy (TEM) as well as energy dispersive X-ray analysis (EDX). On the basis of the Rietveld structure refinements of the XRD spectra at low tin concentrations, it was found that Sn{sup 4+} ions partially substitute for Fe{sup 3+} at the octahedral sites and also occupy the interstitial octahedral sites which are vacant in {alpha}-Fe{sub 2}O{sub 3} corundum structure. A phase separation of {alpha}-Fe{sub 2}O{sub 3} and SnO{sub 2} was observed for x {ge} 0.4: the {alpha}-Fe{sub 2}O{sub 3} structure containing tin decreases simultaneously with the increase of the SnO{sub 2} phase containing substitutional iron ions. The mean particle dimension decreases from 70 nm to 6 nm, as the molar fraction x increases up to x = 1.0. The estimated solubility limits in the nanoparticle system (1-x){alpha}-Fe{sub 2}O{sub 3}-xSnO{sub 2} synthesized under hydrothermal conditions are: x {le} 0.2 for Sn{sup 4+} in {alpha}-Fe{sub 2}O{sub 3} and x {ge} 0.7 for Fe{sup 3+} in SnO{sub 2}. These findings are in press in the Journal of Physics and Chemistry of Solids.
Date: March 1, 2004
Creator: Sorescu, Monica
Partner: UNT Libraries Government Documents Department

Influence of Radiation and Multivalent Cation Additions on Phase Separation and Crystallization of Glass

Description: This report presents results of: (1) measurement of valence state ratios of iron in glass, and (2) a study of the effect of iron redox ratio on phase separation behavior in a glass. The redox ratio of iron in two sodium silicate (NS) glasses has been determined using a colorimetric method, Moessbauer analysis, and optical absorption. The experimental procedures were described in a previous report. We found that these three methods gave excellent agreement for the values of the Fe++/Fe+++ (redox ratio) in the glasses. Also, using the results of the colorimetric analysis we were able to find the extinction coefficients for the18.56% NS and the 13% NS glasses. We have utilized the optical absorption data that was taken for purposes of determining redox ratios to provide glass structural information. In particular, it has been suggested that the band centered near 14,500 cm-1 is indicative of Fe2+ - O2- - Fe3+ formation. In addition, the relative band intensities at 10,000 cm-1 and 4,800 cm-1 could give us information as to the environment around the Fe2+ responsible for the 4,800 cm-1 band. The Moessbauer data will provide supporting structural information. For example, the relative number of clustered and free ferric ions can be computed from the ratio of areas under the doublet and sextet in the liquid He spectra. Also, the change in shift parameter with redox ratio will provide an indication of whether there is an increase or decrease in tetrahedral site symmetry about both ferrous and ferric ions. Finally, the quadrupole splitting parameter provides information regarding the site symmetries about the Fe++ and Fe+++. Currently, we are analyzing the spectral data for these purposes. The Moessbauer work was done in conjunction with colleagues at PNNL, and a manuscript is currently in preparation. The effect of oxidation state of iron ...
Date: August 9, 2002
Creator: Weinberg, Michael C.; Uhlmann, Donald R. & Smith, Gary L.
Partner: UNT Libraries Government Documents Department

The investigation of electron-ion radiative and dielectronic recombination in high-temperature plasmas. Progress report for 1990--1991

Description: (1) The unified description of radiative and dielectronic recombination, which the authors have developed to provide corrections to the conventional independent-processes approximation, has been generalized to self-consistently incorporate the effects of charged-particle collisions and plasma electric fields. (2) The K{sub {alpha}} model for the dielectronic satellite spectra of highly-charged Fe ions, which the authors have developed based on the conventional theory of dielectronic satellite line intensities, has been incorporated into the multi-ion-species transport code MIST. Excellent agreement has been obtained between the simulated spectra and the observed Fe K{sub {alpha}} spectra from PLT and TFTR. (3) A detailed investigation has been completed on the dielectronic recombination satellite spectra in the presence of a distribution of plasma electric microfields. The calculations have been carried out for the lowest-lying n=2 satellites, which are affected by the electric fields only in high-density laser-produced plasma. For application to the lower-density conditions in tokamak plasmas, in which the electron density is about ten orders of magnitude smaller, a number of alternatives are under consideration for evaluating the recombination rates associated with the Rydberg autoionizing sates corresponding to large values of n. (3) A manuscript entitled ``Observation of Density-Enhanced Dielectronic Satellite Spectra Produced During Subpicosecond Laser-Matter Interactions`` has been submitted for publication in the Physical Review A. This work provides a convincing experimental verification of the theoretical predictions on the density sensitivity of diagnostically-important dielectronic satellite spectra in dense plasmas.
Date: December 31, 1991
Creator: Jacobs, V. L.
Partner: UNT Libraries Government Documents Department

Theoretical study of reactions at the electrode-electrolyte interface. Progress report, February 1, 1993--March 31, 1994

Description: Electron transfer rates are predicted by numerical methods, in collaboration with ANL. Emphasis is on electron transfer involving ions known to be important in enhancing stress corrosion cracking in light water reactors and on electron transfer at oxide surfaces. We have completed studies of the ferrous-ferric electron transfer rate in which effects of electric field, entropic effects in the free energy and quantum effects are included for the first time in the calculation of the rate of an electrochemical (heterogeneous) reaction rate. These new results confirm assumptions made in earlier calculations. The ferric ion has been modelled in a dissociable polarizable model showing the six-fold coordination of this ion in aqueous solution is stabilized by the three body interactions arising from the polarizability of water. In our studies of oxides, we have completed a Hartree self consistent calculation of the electronic structure of fayalite. The calculation utilizes a new method which takes phenomenological account of local electron correlations which have plagued electronic structure calculations of oxides for a long time. No electronic structure calculation of fayalite has been previously reported to our knowledge. Similar methods have been used to calculate the electronic structure of a vacancy in rutile (TiO{sub 2}). Results show that the screening donor electrons are anisotropically distributed around the vacancy.
Date: April 1, 1994
Creator: Halley, J. W.
Partner: UNT Libraries Government Documents Department

High-resolution measurements, line identification, and spectral modeling of K{alpha} transitions in Fe XVIII-XXV

Description: The iron K{alpha} emission spectrum covering the wavelength region from 1.840 to 1.940 {Angstrom} is analyzed. Measurements are made with a high-resolution Bragg crystal spectrometer on the Princeton Large Torus (PLT) tokamak for plasma conditions which closely resemble those of solar flares. A total of 40 features are identified consisting of either single or multiple lines from eight charge states in iron, Fe XVIII through Fe XXV, and their wavelengths are determined with an accuracy of 0.1--0.4 m{Angstrom}. Many of these features are identified for the first time. In the interpretation of our observations we rely on model calculations that determine the ionic species abundances from electron density and temperature profiles measured independently with non-spectroscopic techniques and that incorporate theoretical collisional excitation and dielectronic recombination rates resulting in the excitation of the 1s2s{sup r}2p{sup s} configurations. The model calculations also include the effect of diffusive ion transport. Good overall agreement between the model calculations and the observations is obtained, which gives us confidence in our line identifications and spectral modeling capabilities. The results are compared with earlier analyses of the K{alpha} emission from the Sun. While many similarities are found, a few differences arise from the somewhat higher electron density in tokamak plasmas (10{sup 13} cm{sup {minus}3}), which affects the fine-structure level populations of the ground states of the initial ion undergoing electron-impact excitation or dielectronic recombination. We also find that several spectral features are comprised of different transitions from those reported in earlier analyses of solar data.
Date: November 1, 1992
Creator: Beiersdorfer, P.; Phillips, T.; Jacobs, V. L.; Hill, K. W.; Bitter, M.; von Goeler, S. et al.
Partner: UNT Libraries Government Documents Department

Helium, iron and electron particle transport and energy transport studies on the TFTR tokamak

Description: Results from helium, iron, and electron transport on TFTR in L-mode and Supershot deuterium plasmas with the same toroidal field, plasma current, and neutral beam heating power are presented. They are compared to results from thermal transport analysis based on power balance. Particle diffusivities and thermal conductivities are radially hollow and larger than neoclassical values, except possibly near the magnetic axis. The ion channel dominates over the electron channel in both particle and thermal diffusion. A peaked helium profile, supported by inward convection that is stronger than predicted by neoclassical theory, is measured in the Supershot The helium profile shape is consistent with predictions from quasilinear electrostatic drift-wave theory. While the perturbative particle diffusion coefficients of all three species are similar in the Supershot, differences are found in the L-Mode. Quasilinear theory calculations of the ratios of impurity diffusivities are in good accord with measurements. Theory estimates indicate that the ion heat flux should be larger than the electron heat flux, consistent with power balance analysis. However, theoretical values of the ratio of the ion to electron heat flux can be more than a factor of three larger than experimental values. A correlation between helium diffusion and ion thermal transport is observed and has favorable implications for sustained ignition of a tokamak fusion reactor.
Date: March 1, 1993
Creator: Synakowski, E. J.; Efthimion, P. C.; Rewoldt, G.; Stratton, B. C.; Tang, W. M.; Grek, B. et al.
Partner: UNT Libraries Government Documents Department

Particle and energy transport studies on TFTR and implications for helium ash in future fusion devices

Description: Local thermal particle and energy transport studies of balanced-injection L-mode and Supershot deuterium plasmas with the same toroidal field, plasma current, and neutral beam heating power have been performed on TFTR. The particle transport of He{sup 2+} and electrons following a small helium gas puff and Fe{sup 24+} induced by laser ablation has been examined and compared to the local energy transport characteristics inferred from power balance analysis. All particle perturbation diffusivities are radially hollow and are similar in magnitude and shape to the effective thermal conductivities found by power balance analysis. All particle diffusivities are 1--2 orders of magnitude larger than neoclassical values, except near the magnetic axis. A reduction in the helium diffusivity D{sub He} in the Supershot as compared to the L-mode is accompanied by a similar reduction in the effective single fluid thermal conductivity {chi}fluid. Also, the helium core convective velocity V{sub He} is found to increase in the Supershot over the L-Mode for r/a < 0.5. A quasilinear model of electrostatic drift waves has been used to calculate ratios between particle and energy fluxes in the Supershot. The measured ratios of the helium and iron particle diffusivities are in good accord with predictions, as are predicted ratios of V{sub He}/D{sub He}. Modelling indicates that the similarity in magnitude and profile shape of D{sub He} and {chi}fluid has generally favorable implications for helium ash content in a future fusion reactor. The core convection found in the Supershot increases the helium concentration on axis but does not reduce the plasma reactivity significantly.
Date: March 1, 1993
Creator: Synakowski, E. J.; Efthimion, P. C.; Rewoldt, G.; Stratton, B. C.; Tang, W. M.; Bell, R. E. et al.
Partner: UNT Libraries Government Documents Department