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Steiger, J.
Heidelberg Univ. (Germany, F.R.). Naturwissenschaftlich-Mathematische Gesamtfakultaet1989
Heidelberg Univ. (Germany, F.R.). Naturwissenschaftlich-Mathematische Gesamtfakultaet1989
AbstractAbstract
[en] In the Heidelberg Spheromak Experiment two types of double-toroidal plasmas were investigated: Spheromak and tokamak type plasmas. The double toroids were produced by a modified Theta-Z-Pinch technique. Without additional stabilization these plasmas relax into a helical equilibrium. Even with help of figure-8-coils it was not possible to produce cylindrically symmetric configurations, which only worked with use of an isolated axial conductor carrying part of the axial electric current. The equilibrium corresponds to that of a tokamak with small aspect ratio. It was shown that these plasmas relax into a Taylor state. The radial field profiles can be described by a simple analytical model. A numerical solution of the Grad-Shafranov equation explains the axial field distributions. Electron density and temperature were measured through Thomson scattering in order to determine the plasma pressure. The medium beta ratio was found to be 12%. (orig.)
[de]
Am Heidelberger Spheromakexperiment wurden neben Einfachtoroiden auch Doppeltoroide erzeugt. Die experimentellen Untersuchungen am HSE lassen sich in zwei Bereiche einteilen: 1. spheromakaehnliche Plasmen: Doppeltoroide ohne zusaetzliche stabilisierende Massnahmen beziehungsweise durch Figur-8-Spulen stabilisierte Doppeltoroide. 2. tokamakaehnliche Plasmen: Doppeltoroide mit axialem Leiter entlang der Symmetrieachse. Die untersuchten Doppeltoroide wurden durch eine modifizierte Θ-Z-Pinch Technik erzeugt. Ohne zusaetzliche Stabilisierung relaxieren diese Plasmen in ein helisches Gleichgewicht. Auch durch den Einsatz von Figur-8-Spulen konnten keine zylindersymmetrischen Konfigurationen hergestellt werden. Durch den Einbau eines nicht isolierten, axialen Leiters, den einen Teil des axialen Stroms traegt, konnten zylindersymmetrische Plasmen mit Feldumkehrzeiten bis zu 80 μs erzeugt werden. Das entstandene Gleichgewicht entspricht dem eines Tokamaks mit kleinem Aspektverhaeltnis. Es konnte gezeigt werden, dass diese Plasmen, ebenso wie der Spheromak, in einen Taylorschen Zustand relaxieren. Die radialen Feldprofile lassen sich durch ein einfaches analytisches Modell beschreiben. Eine numerische Loesung der Grad-Shafranov-Gleichung, die auch die Abhaengigkeit des Flusses von z beruecksichtigt, erklaert den axialen Verlauf der Felder. Zur Bestimmung des Plasmadrucks wurden Elektronendichte und Temperatur mittels Thomsonstreung gemessen. Die so bestimmten Druecke sind mit der Annahme einer im Fluss linearen Druckfunktion vertraeglich; sie stimmen mit den aus den magnetischen Messungen bestimmten Druecken im Rahmen der Messgenauigkeit ueberein. Das mittlere Beta betraegt in den hier untersuchten Plasmen ungefaehr 12%. (orig.)Original Title
Untersuchungen von Plasmen doppeltoroidaler Struktur vom Typ des Spheromaks und des Spherical Torus am Heidelberger Spheromak Experiment
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1989; 98 p; Available from the library of Heidelberg Univ. (Germany, F.R.); Diss. (Dr.rer.nat.).
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Beck, B. R.; Church, D. A.; Gruber, L.; Holder, J. P.; Schneider, D.; Steiger, J.
Lawrence Livermore National Lab., CA (United States). Funding organisation: USDOE Office of Defense Programs (DP) (United States)1998
Lawrence Livermore National Lab., CA (United States). Funding organisation: USDOE Office of Defense Programs (DP) (United States)1998
AbstractAbstract
[en] Storage rings and Penning traps are being used to study ions in their highest charge states. Both devices must have the capability for ion cooling in order to perform high precision measurements such as mass spectrometry and laser spectroscopy. This is accomplished in storage rings in a merged beam arrangement where a cold electron beam moves at the speed of the ions. In RETRAP, a Penning trap located at Lawrence Livermore National Laboratory, a sympathetic laser/ion cooling scheme has been implemented. In a first step, singly charged beryllium ions are cooled electronically by a tuned circuit and optically by a laser. Then hot, highly charged ions are merged into the cold Be plasma. By collisions, their kinetic energy is reduced to the temperature of the Be plasma. First experiments indicate that the highly charged ions form a strongly coupled plasma with a Coulomb coupling parameter
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22 Oct 1998; 243 Kilobytes; International Conference on Trapped Charged Particles and Fundamental Physics; Monterey, CA (United States); 31 Aug - 4 Sep 1998; DP--0102012/96-ERD-052; W-7405-ENG-48; Available from PURL: https://www.osti.gov/servlets/purl/2835-abhWdi/native/
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Beck, B. R.; Church, D. A.; Gruber, L.; Holder, J. P.; Schneider, D.; Steiger, J.
Lawrence Livermore National Lab., CA (United States). Funding organisation: USDOE Office of Defense Programs (DP) (United States)1998
Lawrence Livermore National Lab., CA (United States). Funding organisation: USDOE Office of Defense Programs (DP) (United States)1998
AbstractAbstract
[en] In the past few years a cryogenic Penning trap (RETRAP) has been operational at the Electron Beam Ion Trap (EBIT) facility at Lawrence Livermore National Laboratory. The combination of RETRAP and EBIT provides a unique possibility of producing and re-trapping highly charged ions and cooling them to very low temperatures. Due to the high Coulomb potentials in such an ensemble of cold highly charged ions the Coulomb coupling parameter (the ratio of Coulomb potential to the thermal energy) can easily reach values of 172 and more. To study such systems is not only of interest in astrophysics to simulate White Dwarf star interiors but opens up new possibilities in a variety of areas (e.g. laser spectroscopy), cold highly charged ion beams
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22 Oct 1998; 216 Kilobytes; 15. International Conference on the Application of Accelerators in Research and Industry; Denton, TX (United States); 4-7 Nov 1998; DP--0102012/96-ERD-052; W-7405-ENG-48; Available from PURL: https://www.osti.gov/servlets/purl/2836-eaks8X/native/
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[en] The resonant nuclear reaction 1H(15N,αγ)12C was used to measure hydrogen concentrations in thin Nb films as a function of the external H2 pressure (H solubility). Experiments were performed in the pressure range up to 1 mbar and temperatures between 166 and 200 degree C, i.e., in the region around the critical temperature (177 degree C) of the α-α' phase transition. We find that the hydrogen solubility in thin epitaxial films is considerably reduced compared to bulk data. The analysis of the data within mean-field theory for a lattice gas shows that the H-Nb interaction remains, within the experimental error, unchanged with respect to the bulk value but that the attractive H-H interaction energy is strongly reduced (0.1 eV in the film compared to 0.2 eV in the bulk). The difference is attributed to strain effects due to the clamping of the films to the substrate
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CHEMICAL ANALYSIS, CHEMICAL REACTIONS, DECAY, ELECTROMAGNETIC RADIATION, ELEMENTS, FILMS, HEAVY ION REACTIONS, IONIZING RADIATIONS, METALS, NONDESTRUCTIVE ANALYSIS, NONMETALS, NUCLEAR DECAY, NUCLEAR REACTIONS, PHYSICAL PROPERTIES, PLATINUM METALS, RADIATIONS, TEMPERATURE RANGE, THERMODYNAMIC PROPERTIES, TRANSITION ELEMENTS, TRANSITION TEMPERATURE
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[en] Investigations of the behavior of hydrogen in thin Nb-Hf-Nb layers were performed by the nuclear reaction 1H(15N, αγ)12C. The preparation of the samples as well as first studies of the surfaces and interfaces of this system by Auger electron spectroscopy and low-energy electron diffraction are described. The influence of lattice distortions at the metal-metal interfaces on the depth profile of the hydrogen concentration is discussed. (orig.)
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1. European conference on accelerators in applied research and technology (ECAART-1); Frankfurt am Main (Germany, F.R.); 5-9 Sep 1989
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Nuclear Instruments and Methods in Physics Research, Section B; ISSN 0168-583X; ; CODEN NIMBE; v. 50(1-4); p. 31-34
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[en] Multicomponent non-neutral ion plasmas in a Penning trap consisting of Be+ and highly charged Xe ions, having different mass-to-charge ratios than Be+ , are cooled to form strongly coupled plasmas by applying a laser-based collisional cooling scheme. The temperature of the plasma was determined from a Doppler broadened transition in Be+ . For the Xe ions, which are centrifugally separated from the Be, the Coulomb coupling parameter was estimated to be ∼1000 . Molecular dynamics simulations of the ion mixture show ordered structures, indicating crystallization of the Xe
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Othernumber: PRLTAO000086000004000636000001; 040103PRL; The American Physical Society
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Physical Review Letters; ISSN 0031-9007; ; v. 86(4); p. 636-639
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[en] The retrapping of highly charged Xe44+ and Th68+,72+ ions extracted from an ''electron-beam ion trap'' (EBIT) is demonstrated after injection of the ions into RETRAP, a cryogenic Penning trap (up to 6 T magnetic field) currently with an open cylinder design. Ion extraction in a short pulse (5--20 μs) from EBIT, essential for efficient retrapping, is employed. The ions are slowed down upon entering a deceleration tube mounted above the trap within the magnetic field. The potential is then rapidly (100 ns) decreased, enabling low-energy ions to enter the trap. Capture efficiencies up to 25% are observed via detection of the delayed ion release pulse with a detector below the trap. Signal voltages induced in a tuned circuit due to single and multiple ions have been observed by tuning the ion resonant axial oscillation frequencies for different ions. Results from transporting and retrapping of the ions, as well as their detection, are described and the trapping efficiency is discussed. The motivation for these studies is to cool the trapped very highly charged ions to low temperatures (<4 K) in order to perform ultrahigh-resolution precision spectroscopy, collision studies at ultralow energies, and to observe phase transitions in Coulomb clusters of highly charged ions
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[en] A vacuum toroidal field has been superimposed on a spheromak by means of an axial conductor. It has been observed that the resulting configuration corresponds to a tokamak with limiting low aspect ratio, i.e. a spherical torus with aspect ratio 1.1. The corresponding spheromak is unstable to n = 1 tilt and shift modes, but this tokamak configuration is found to be globally stable without additional passive stabilization. (author). Letter-to-the-editor. 11 refs, 4 figs
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Erxmeyer, J.; Dortmann, G.; Balogh, A.; Steiger, J.; Boebel, O.; Weidinger, A.; Stritzker, B.; Zander, W.
High-temperature superconductors. Materials aspects. Proceedings. Vol. 21991
High-temperature superconductors. Materials aspects. Proceedings. Vol. 21991
AbstractAbstract
[en] The main idea of this experiment is to use hydrogen as an electron donor to change the carrier concentration in high-Tc superconductors. The dependence of the superconducting properties, in particular the superconducting transition temperature on the carrier concentration is of great importance for the understanding of the pairing mechanism in these materials. In this work, the effect of hydrogen charging on the electrical resistivity, the change of the superconducting transition temperature and the Hall number was studied. We find that the concentration of charge carriers is strongly reduced by hydrogen doping. The data can be understood assuming that hydrogen compensates the (hole) charge carriers in YBaCuO. In contrast, the superconducting transition temperature is not much affected by H-doping in the concentration range studied. (orig.)
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Freyhardt, H.C.; Fluekiger, R.; Peuckert, M. (eds.); 588 p; ISBN 3-88355-163-5; ; 1991; p. 891-894; DGM Informationsgesellschaft Verl; Oberursel (Germany); ICMC topical conference on high-temperature superconductors (HTSC): Materials aspects; Fachtagung ueber Hochtemperatur-Supraleiter (HTSL): Materialentwicklung; Garmisch-Partenkirchen (Germany); 9-11 May 1990
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Book
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ALKALINE EARTH METAL COMPOUNDS, AMINES, BARIUM COMPOUNDS, CHALCOGENIDES, COPPER COMPOUNDS, ELECTRICAL PROPERTIES, FILMS, MATERIALS, ORGANIC COMPOUNDS, OXIDES, OXYGEN COMPOUNDS, PHYSICAL PROPERTIES, SUPERCONDUCTORS, TEMPERATURE RANGE, THERMODYNAMIC PROPERTIES, TRANSITION ELEMENT COMPOUNDS, YTTRIUM COMPOUNDS
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[en] Electron transfer from H2 to Th79+ was studied in a cryogenic Penning trap by non-destructively observing the sequential development with time of the charge state of one or a few stored particles. The ratio of the true double capture cross section to the total capture cross section was found to be 0.21 ± 0.11 at a mean center-of-mass energy near 6 eV. (orig.)
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2. Euroconference on atomic physics with stored highly charged ions; Stockholm (Sweden); 3-7 Jun 1996; 8 refs.
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