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Projectile-charge-state dependence of target L-shell ionization by 1.86-MeV/amu fluorine and silicon ions and 1.8-MeV/amu chlorine ions

Description: This article discusses projectile-charge-state dependence of target L-shell ionization by 1.86-MeV/amu and silicon ions and 1.8-MeV/amu chlorine ions.
Date: April 1979
Creator: McDaniel, Floyd Del. (Floyd Delbert), 1942-; Toten, R. S.; Peterson, J. L.; Duggan, Jerome L.; Wilson, Scott R.; Gressett, J. D. et al.
Partner: UNT College of Arts and Sciences

Perspective on the Role of Negative Ions and Ion-Ion Plasmas in Heavy Ion Fusion Science, Magnetic Fusion Energy,and Related Fields

Description: Some years ago it was suggested that halogen negative ions could offer a feasible alternative path to positive ions as a heavy ion fusion driver beam which would not suffer degradation due to electron accumulation in the accelerator and beam transport system, and which could be converted to a neutral beam by photodetachment near the chamber entrance if desired. Since then, experiments have demonstrated that negative halogen beams can be extracted and accelerated away from the gas plume near the source with a surviving current density close to what could be achieved with a positive ion of similar mass, and with comparable optical quality. In demonstrating the feasibility of halogen negative ions as heavy ion driver beams, ion - ion plasmas, an interesting and somewhat novel state of matter, were produced. These plasmas, produced near the extractor plane of the sources, appear, based upon many lines of experimental evidence, to consist of almost equal densities of positive and negative chlorine ions, with only a small component of free electrons. Serendipitously, the need to extract beams from this plasma for driver development provides a unique diagnostic tool to investigate the plasma, since each component - positive ions, negative ions, and electrons - can be extracted and measured separately. We discuss the relevance of these observations to understanding negative ion beam extraction from electronegative plasmas such as halogens, or the more familiar hydrogen of magnetic fusion ion sources. We suggest a concept which might improve negative hydrogen extraction by the addition of a halogen. The possibility and challenges of producing ion - ion plasmas with thin targets of halogens or, perhaps, salt, is briefly addressed.
Date: August 1, 2008
Creator: Grisham, L. R. & Kwan, J. W.
Partner: UNT Libraries Government Documents Department

Amorphization and the effect of implanted ions in SiC

Description: The effects of implanted ion chemistry and displacement damage on the amorphization threshold dose of SiC were studied using cross-section transmission electron microscopy. Room temperature as well as 200 and 400 C irradiations were carried out with 3.6 MeV Fe, 1.8 MeV Cl, 1 MeV He or 0.56 MeV Si ions. The room temperature amorphization threshold dose in irradiated regions well separated from the implanted ions was found to range from 0.3 to 0.5 dpa for the four different ion species. The threshold dose for amorphization in the He, Si and Fe ion-implanted regions was also {approximately}0.3 to 0.5 dpa. On the other hand, the amorphization threshold in the Cl-implanted region was only about 0.1 dpa. The volume change associated with amorphization was {approximately}17%. No evidence for amorphization was obtained in specimens irradiated at 200 or 400 C. An understanding of the microstructural evolution of SiC under irradiation is critical to the application of these materials in fusion energy systems.
Date: December 31, 1994
Creator: Snead, L.L. & Zinkle, S.J.
Partner: UNT Libraries Government Documents Department

Semiempirical studies of atomic structure. Progress report, 1 March 1992--15 December 1992

Description: The energy level structure, transition probabilities, and general spectroscopic properties of highly ionized many-electron systems are studied through the combined use of sensitive semiempirical data systematizations, selected precision experimental measurements, and specialized theoretical computations. Measurements are made primarily through the use of fast ion beam excitation methods, which are combined with available data from laser-and tokamak-produced plasmas, astrophysical sources, and conventional light sources. The experimental studies are strengthened through large-scale ab initio calculations. Typical examples are the following: lifetime measurements in the neon isoelectronic sequence; multiplexed decay curve measurements of Li-like Si XII; and isoelectronic specification of intershell resonance and intercombination decay rates using measured transition probabilities and spectroscopically determined singlet-mixing amplitudes.
Date: December 31, 1992
Creator: Curtis, L. J.
Partner: UNT Libraries Government Documents Department

Perspective on the Role of Negative Ions and Ion-Ion Plasmas in Heavy Ion Fusion Science, Magnetic Fusion Energy, and Related Fields

Description: Some years ago it was suggested that halogen negative ions [1]could offer a feasible alternative path to positive ions as a heavy ion fusion driver beam which would not suffer degradation due to electron accumulation in the accelerator and beam transport system, and which could be converted to a neutral beam by photodetachment near the chamber entrance if desired. Since then, experiments have demonstrated that negative halogen beams can be extracted and accelerated away from the gas plume near the source with a surviving current density close to what could be achieved with a positive ion of similar mass, and with comparable optical quality. In demonstrating the feasibility of halogen negative ions as heavy ion driver beams, ion - ion plasmas, an interesting and somewhat novel state of matter, were produced. These plasmas, produced near the extractor plane of the sources, appear, based upon many lines of experimental evidence, to consist of almost equal densities of positive and negative chlorine ions, with only a small component of free electrons. Serendipitously, the need to extract beams from this plasma for driver development provides a unique diagnostic tool to investigate the plasma, since each component - positive ions, negative ions, and electrons -- can be extracted and measured separately. We discuss the relevance of these observations to understanding negative ion beam extraction from electronegative plasmas such as halogens, or the more familiar hydrogen of magnetic fusion ion sources. We suggest a concept which might improve negative hydrogen extraction by the addition of a halogen. The possibility and challenges of producing ion-ion plasmas with thin targets of halogens or, perhaps, salt, is briefly addressed.
Date: August 1, 2008
Creator: Grisham, L.R. & Kwan, J.W.
Partner: UNT Libraries Government Documents Department

A Negative-Surface Ionization for Generation of Halogen Radioactive Ion Beams

Description: A simple and efficient negative surface ionization source has been designed, fabricated and initially tested for on-line generation of radioactive ion beams of the halogens (Cl, Br, I, and At) for use in the nuclear-structure and nuclear-astrophysics research programs at the Holifield Radioactive Ion Beam Facility. The source utilizes a solid, spherical geometry LaB{sub 6} surface ionizer for forming highly electronegative atoms and molecules. Despite its widely publicized propensity for being easily poisoned, no evidences of this effect were experienced during testing of the source. Nominal efficiencies of 15% for Br{sup {minus}} beam generation were obtained during off-line evaluation of the source with AlBr3 feed material when account is taken of the fractional dissociation of the molecule. Principles of operation, design features, operational parameter data, initial performance results, and beam quality data (emittance) are presented in this article.
Date: April 16, 2001
Creator: Zaim, H.
Partner: UNT Libraries Government Documents Department

Target selection for the HRIBF Project

Description: Experiments are in progress at the Oak Ridge National Laboratory (ORNL) which are designed to select the most appropriate target materials for generating particular radioactive ion beams for the Holifield Radioactive Ion Beam Facility (HRIBF). The 25-MV tandem accelerator is used to implant stable complements of interesting radioactive elements into refractory targets mounted in a high-temperature FEBIAD ion source which is on-line at the UNISOR facility. These experiments permit selection of the target material most appropriate for the rapid release of the element of interest, as well as realistic estimates of the efficiency of the FEBIAD source. From diffusion release data information on the release times and diffusion coefficients can be derived. Diffusion coefficients for CI implanted into and diffused from CeS and Zr{sub 5}Si{sub 3} and As, Br, and Se implanted into and diffused from Zr{sub 5}Ge{sub 3} have been derived from the resulting intensity versus time profiles.
Date: December 31, 1994
Creator: Dellwo, J.; Alton, G.D. & Batchelder, J.C.
Partner: UNT Libraries Government Documents Department

Experimental evaluation of a negative ion source for a heavy ionfusion negative ion driver

Description: Negative halogen ions have recently been proposed as a possible alternative to positive ions for heavy ion fusion drivers because electron accumulation would not be a problem in the accelerator, and if desired, the beams could be photodetached to neutrals [1,2,3]. To test the ability to make suitable quality beams, an experiment was conducted at Lawrence Berkeley National Laboratory using chlorine in an RF-driven ion source. Without introducing any cesium (which is required to enhance negative ion production in hydrogen ion sources) a negative chlorine current density of 45 mA/cm{sup 2} was obtained under the same conditions that gave 57 mA/cm{sup 2} of positive chlorine, suggesting the presence of nearly as many negative ions as positive ions in the plasma near the extraction plane. The negative ion spectrum was 99.5% atomic chlorine ions, with only 0.5% molecular chlorine, and essentially no impurities. Although this experiment did not incorporate the type of electron suppression technology that is used in negative hydrogen beam extraction, the ratio of co-extracted electrons to Cl{sup -} was as low as 7 to 1, many times lower than the ratio of their mobilities, suggesting that few electrons are present in the near-extractor plasma. This, along with the near-equivalence of the positive and negative ion currents, suggests that the plasma in this region was mostly an ion-ion plasma. The negative chlorine current density was relatively insensitive to pressure, and scaled linearly with RF power. If this linear scaling continues to hold at higher RF powers, it should permit current densities of 100 mA/cm{sup 2}, sufficient for present heavy ion fusion injector concepts. The effective ion temperatures of the positive and negative ions appeared to be similar and relatively low for a plasma source.
Date: January 18, 2005
Creator: Grisham, L. R.; Hahto, S. K.; Hahto, S. T.; Kwan, J. W. & Leung, K. N.
Partner: UNT Libraries Government Documents Department

Experimental Evaluation of a Negative Ion Source for a Heavy Ion Fusion Negative Ion Driver

Description: Negative halogen ions have recently been proposed as a possible alternative to positive ions for heavy ion fusion drivers because electron accumulation would not be a problem in the accelerator, and if desired, the beams could be photo-detached to neutrals. To test the ability to make suitable quality beams, an experiment was conducted at Lawrence Berkeley National Laboratory using chlorine in an RF-driven ion source. Without introducing any cesium (which is required to enhance negative ion production in hydrogen ion sources) a negative chlorine current density of 45 mA/cm{sup 2} was obtained under the same conditions that gave 57 45 mA/cm{sup 2} of positive chlorine, suggesting the presence of nearly as many negative ions as positive ions in the plasma near the extraction plane. The negative ion spectrum was 99.5% atomic chlorine ions, with only 0.5% molecular chlorine, and essentially no impurities. Although this experiment did not incorporate the type of electron suppression technology that i s used in negative hydrogen beam extraction, the ratio of co-extracted electrons to Cl{sup -} was as low as 7 to 1, many times lower than the ratio of their mobilities, suggesting that few electrons are present in the near-extractor plasma. This, along with the near-equivalence of the positive and negative ion currents, suggests that the plasma in this region was mostly an ion-ion plasma. The negative chlorine current density was relatively insensitive to pressure, and scaled linearly with RF power. If this linear scaling continues to hold at higher RF powers, it should permit current densities of 100 45 mA/cm{sup 2}, sufficient for present heavy ion fusion injector concepts. The effective ion temperatures of the positive and negative ions appeared to be similar and relatively low for a plasma source.
Date: June 16, 2004
Creator: L.R. Grisham, S.K. Hahto, S.T. Hahto, J.W. Kwan, and K.N. Leung
Partner: UNT Libraries Government Documents Department

Semiempirical studies of atomic structure. [Dept. of Physics and Astronomy, Univ. of Toledo]

Description: The energy level structure, transition probabilities, and general spectroscopic properties of highly ionized many-electron systems are studied through the combined use of sensitive semiempirical data systematizations, selected precision experimental measurements, and specialized theoretical computations. Measurements are made primarily through the use of fast ion beam excitation methods, which are combined with available data from laser-and tokamak-produced plasmas, astrophysical sources, and conventional light sources. The experimental studies are strengthened through large-scale ab initio calculations. Typical examples are the following: lifetime measurements in the neon isoelectronic sequence; multiplexed decay curve measurements of Li-like Si XII; and isoelectronic specification of intershell resonance and intercombination decay rates using measured transition probabilities and spectroscopically determined singlet-mixing amplitudes.
Date: January 1, 1992
Creator: Curtis, L.J.
Partner: UNT Libraries Government Documents Department

Excited state populations and charge-exchange of fast ions in solids

Description: Excited state populations and charge state fractions of 445 MeV Cl ions have been measured for a range of thicknesses of solid C targets. Cross sections for electron capture, loss, excitation and excited state quenching have been determined and these data are found to predict a quantitative difference between equilibrium charge state distributions from gases and solids for a special case of the Bohr-Lindhard density effect model. 8 references, 1 figure, 1 table.
Date: January 1, 1984
Creator: Miller, P.D.; Sofield, C.J.; Woods, C.J.; Cowern, N.E.B.; Bridwell, L.B.; Moak, C.D. et al.
Partner: UNT Libraries Government Documents Department

Investigations of molecular orbitals with accel-decel beams

Description: Quasimolecular transition energies can be found directly from the impact-parameter dependence of interference structure observed in measured K x-ray spectra. As these experiments require a K-vacancy bearing projectile at collision velocities small compared to the equivalent K-shell electron velocity, the accel-decel technique has to be used. Such an experiment was performed at the BNL Tandem Accel-Decel Facility for collisions of Cl/sup 16 +/ with Ar at energies ranging from 2.5 to 20 MeV. A new method of analysis using the uniform asymptotic approximation is described here. Quasimolecular transition energies derived using this method are compared to results of a previous analysis based on the determination of the relative positions of maxima and minima in the interference patterns. 6 references, 3 figures.
Date: September 1, 1984
Creator: Meron, M.; Johnson, B.M.; Jones, K.W.; Schuch, R.; Schmidt-Boecking, H. & Tserruya, I.
Partner: UNT Libraries Government Documents Department

Line intensities for diagnosing laser-produced plasmas

Description: We have measured relative line intensities of the K x-ray spectra of Si, Cl, and Ca from laser-produced plasmas to assess their usefulness as a plasma diagnostic. The different elements are added at low concentrations to CH disks which are irradiated at 5 x 10/sup 14/ W/cm/sup 2/ with a 0.53 ..mu..m laser pulse of 20 Joules at 1 nsec. The concentration of each element is kept low in order not to change the Z of the plasma, and therefore the plasma dynamics. The various spectra are measured with a time-resolved spectrograph to obtain line intensities as a function of time over the length of the laser pulse. These relative intensities of various He-like and H-like lines are compared with calculations from a steady-state level population code. The results give good consistency among the various line ratios. Agreement is not as good for analysis of the Li-like satellite lines. Modelling of the Li-like lines need further investigation. 10 references, 9 figures.
Date: October 31, 1983
Creator: Kauffman, R.L.; Matthews, D.L.; Lee, R.W.; Whitten, B.L. & Kilkenny, J.D.
Partner: UNT Libraries Government Documents Department

Experimental approaches to the measurement of dielectronic recombination

Description: In dielectronic recombination, the first step involves a continuum electron which excites a previously bound electron and, in so doing, loses just enough energy to be captured in a bound state (nl). This results in a doubly excited ion of a lower charge state which may either autoionize or emit a photon resulting in a stabilized recombination. The complete signature of the event is an ion of reduced charge and an emitted photon. Methods of measuring this event are discussed.
Date: January 1, 1984
Creator: Datz, S.
Partner: UNT Libraries Government Documents Department

Solvation in supercritical water

Description: The aim of this work is to determine the solvation structure in supercritical water composed with that in ambient water and in simple supercritical solvents. Molecular dynamics studies have been undertaken of systems that model ionic sodium and chloride, atomic argon, and molecular methanol in supercritical aqueous solutions using the simple point charge model of Berendsen for water. Because of the strong interactions between water and ions, ionic solutes are strongly attractive in supercritical water, forming large clusters of water molecules around each ion. Methanol is found to be a weakly-attractive solute in supercritical water. The cluster of excess water molecules surrounding a dissolved ion or polar molecule in supercritical aqueous solutions is comparable to the solvent clusters surrounding attractive solutes in simple supercritical fluids. Likewise, the deficit of water molecules surrounding a dissolved argon atom in supercritical aqueous solutions is comparable to that surrounding repulsive solutes in simple supercritical fluids. The number of hydrogen bonds per water molecule in supercritical water was found to be about one third the number in ambient water. The number of hydrogen bonds per water molecule surrounding a central particle in supercritical water was only mildly affected by the identify of the central particle--atom, molecule, or ion. These results should be helpful in developing a qualitative understanding of important processes that occur in supercritical water. 29 refs., 6 figs.
Date: January 1, 1991
Creator: Cochran, H.D. (Oak Ridge National Lab., TN (USA)); Cummings, P.T. & Karaborni, S. (Virginia Univ., Charlottesville, VA (USA). Dept. of Chemical Engineering)
Partner: UNT Libraries Government Documents Department

Dielectronic recombination measurements of multicharged ions

Description: Dielectronic recombination rates have been measured for several charge states of isoelectronic Li-like, Be-like, B-like, and Na-like ions. The amount of electron capture attending the passage of MeV/nucleon ion beams through a collinear, magnetically confined space-charge-limited electron beam as a function of relative energy has been observed. The experimental rates are consistent in magnitude and shape with rates determined from distorted-wave calculations of the dielectronic-recombination cross sections. 72 refs., 6 figs.
Date: January 1, 1987
Creator: Dittner, P.F.
Partner: UNT Libraries Government Documents Department

Chemical applications of molecular quantum theory

Description: Molecular systems of chemical interest are investigated with the aid of molecular quantum theory. The self-consistent field (SCF) method is used to predict the molecular structures of ClF/sub 2/, ClF/sub 4/ and Cl/sub 3/ radicals, and the ions ClF/sub 2//sup +/, ClF/sub 2//sup -/, ClF/sub 4//sup +/ and ClF/sub 4//sup -/. The ClF/sub 2/ and Cl/sub 3/ radicals are predicted to be bent with bond angles of 145.2/sup 0/ and 158.6/sup 0/, respectively, while the ions ClF/sub 2//sup +/ and ClF/sub 2//sup -/ are predicted to be bent with a bond angle of 97.4/sup 0/ and linear, respectively. The geometry predictions for the ClF/sub 4/ radical and the ClF/sub 4//sup +/ ion are found to be notably basis set dependent. The ClF/sub 4//sup -/ ion is predicted to be square-planar. Multi-configuration self-consistent field (MCSCF) calculations have yielded the dipole moment function for the /sup 1/sigma/sup +/ state of HI, which qualitatively confirms the experimental finding that the dipole derivative at R/sub e/ is negative. The /sup 2/sigma/sup +/ F + H/sub 2/ potential energy surface is studied extensively with the configuration interaction (CI) method. The most complete calculations yield an activation energy of 2.74 kcal/mole and an exothermicity of 30.0 kcal/mole. The production of a potential energy surface of ''chemical accuracy'' for this system is found to be more difficult than previously believed. The simplest hydrophobic model, the water-methane system, is studied with the SCF method in order to determine the nature and magnitude of the interaction. The most favorable geometric arrangement corresponds to an attraction of 0.5 kcal/mole.
Date: September 1, 1977
Creator: Ungemach, S.R.
Partner: UNT Libraries Government Documents Department

Atomic collision experiments utilizing low-velocity, highly-charged ion beams

Description: Intense beams of highly-stripped ions are now routinely produced at low velocities using the Brookhaven dual MP-tandens in a unique four-stage accel/decel mode. This mode of operation combines three stages of acceleration, stripping at high energy, and one stage of deceleration to near-zero velocity. To date, experiments have used 10-100 nA beams of bare and few-electron heavy ions at energies as low as 0.2 MeV/amu, and upgrades of the facility should push the lower limit below 0.1 MeV/amu. Recent experiments, such as measurements of charge transfer and x-ray production for S/sup 6-16+/ on He and Ar at 6 to 20 MeV and P(b) measurements for MO x-rays produced in Cl/sup 16 +/ + Ar collisions at 20, 10, and 5 MeV have demonstrated the usefulness of highly-stripped, low-velocity projectiles. These experiments and a few possibilities for future experiments are discussed.
Date: January 1, 1982
Creator: Johnson, B.M.; Jones, K.W. & Meron, M.
Partner: UNT Libraries Government Documents Department