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  • Elsevier  (353)
  • Springer Nature  (50)
  • American Institute of Physics  (46)
  • American Geophysical Union  (45)
  • American Institute of Physics (AIP)  (33)
  • 1995-1999  (382)
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  • 1
    Publikationsdatum: 1997-11-01
    Print ISSN: 0723-2020
    Digitale ISSN: 1618-0984
    Thema: Biologie
    Publiziert von Elsevier
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3369-3387 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Particle-in-cell simulations of applied-B ion diodes using the QUICKSILVER code [D. B. Seidel et al., in Proceedings of the Europhysics Conference on Computational Physics, Amsterdam, 1990, edited by A. Tenner (World Scientific, Singapore, 1991), p. 475] have been augmented with Monte Carlo calculations of electron–anode interactions (reflection and energy deposition). Extraction diode simulations demonstrate a link between the instability evolution and increased electron loss and anode heating. Simulations of radial and extraction ion diodes show spatial nonuniformity in the predicted electron loss profile leading to hot spots on the anode that rapidly exceed the 350 °C–450 °C range, known to be sufficient for plasma formation on electron-bombarded surfaces. Thermal desorption calculations indicate complete desorption of contaminants with 15–20 kcal/mole binding energies in high-dose regions of the anode during the power pulse. Comparisons of parasitic ion emission simulations and experiment show agreement in some aspects, but also highlight the need for better ion source, plasma, and neutral gas models. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2175-2182 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Magnetically insulated ion diodes are being developed to drive inertial confinement fusion. Ion beam microdivergence must be reduced to achieve the very high beam intensities required to achieve this goal. Three-dimensional particle-in-cell simulations [Phys. Rev. Lett. 67, 3094 (1991)] indicate that instability-induced fluctuations can produce significant ion divergence during acceleration. These simulations exhibit a fast growing mode early in time, which has been identified as the diocotron instability. The divergence generated by this mode is modest, due to the relatively high-frequency ((approximately-greater-than)1 GHz). Later, a low-frequency low-phase-velocity instability develops with a frequency that is approximately the reciprocal of the ion transit time. This instability couples effectively to the ions, and can generate unacceptably large ion divergences ((approximately-greater-than)30 mrad). Linear stability theory reveals that this mode has structure parallel to the applied magnetic field and is related to the modified two-stream instability. Measurements of ion density fluctuations and energy-momentum correlations have confirmed that instabilities develop in ion diodes and contribute to the ion divergence. In addition, spectroscopic measurements indicate that lithium ions have a significant transverse temperature very close to the emission surface. Passive thin-film lithium fluoride (LiF) anodes have larger transverse beam temperatures than laser-irradiated active sources. Calculations of the ion beam source divergence for the LiF film due to surface roughness and the possible loss of adhesion and fragmentation of this film are presented. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Calculations are presented for a high yield inertial fusion design, employing indirect drive with a double-ended z-pinch-driven hohlraum radiation source. A high current (∼60 MA) accelerator implodes z pinches within an enclosing hohlraum. Radial spoke arrays and shine shields isolate the capsule from the pinch plasma, magnetic field, and direct x-ray shine. Our approach places minimal requirements on z-pinch uniformity and stability, usually problematic due to magneto-Rayleigh–Taylor instability. Large inhomogeneities of the pinch and spoke array may be present, but the hohlraum adequately smooths the radiation field at the capsule. Simultaneity and reproducibility of the pinch x-ray output to better than 7% are required, however, for good symmetry. Recent experiments suggest a pulse shaping technique, through implosion of a multishell z pinch. X-ray bursts are calculated and observed to occur at each shell collision. A capsule absorbing 1 MJ of x rays at a peak drive temperature of 210 eV is found to have adequate stability and to produce 400 MJ of yield. A larger capsule absorbs 2 MJ with a yield of 1200 MJ. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2963-2969 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In a recent paper [A. D. Bailey et al., Phys. Rev. Lett. 34, 3124 (1993)], the authors presented direct planar laser induced fluorescence measurements of the oscillatory ion fluid velocity field in the presence of a large amplitude drift-Alfven wave. Surprisingly, the measured speeds were an order of magnitude lower than predicted by standard fluid theory, yet the flow pattern was consistent with the fluid theory. A new model, based on the connection between stochasticity and bulk behavior, is presented which gives insights into the cause of this behavior. It is shown that when particle motion is stochastic, invariant sets of a ‘Poincaré map' define a flat-topped particle distribution function consistent with both the electromagnetic field driving the Vlasov equation and the fine-scale single particle dynamics. The approach is described for the general case and explored for a slab model of the observed drift wave. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1051-1054 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We have developed and tested a multilayer mirror (MLM) polarimeter optimized for λ=304 Å using electron impact on helium. Specifically we present the first experimental results of the polarization of the extreme ultraviolet Lyman-α emission from He+ [He II (2p)2P°→(1s)2S] as a function of the electron impact energy for impact energies ranging from 150 to 980 eV. A major challenge to performing this measurement is the suppression of the dominant He I (1snp)1P°→(1s2)1S radiation originating from the excitation of helium. Excellent spectral selectivity has been achieved with a VYNS copolymer filter whose transmission ratio of He II to He I emission has been measured to be greater than 1200:1. Additionally, we have measured the instrumental polarization using two identical MLMs in a crossed polarizer configuration. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Kα emission spectroscopy is an important diagnostic technique used for plasmas created in intense light ion beam experiments.b),c) Emission lines can be produced as 2p electrons drop down to fill 1s vacancies created by the ion beam. Bailey et al.b) reported the first spectroscopic measurements of Kα x-ray satellites in intense proton beam experiments on PBFA-II at Sandia. Kα emission spectra have also recently been observed in intense Li-beam experiments on PBFA-II.d) Two approaches are used to analyze time-integrated x-ray spectra. In the first, CRE calculations are performed to compute synthetic time-integrated spectra using plasma conditions predicted from radiation-hydrodynamic simulations. In the second approach, plasma conditions are deduced from Kα satellite line intensity ratios measured from the highest ionization stages observed in the experiments. Results will be presented from our analysis of recent PBFA-II x-ray spectra. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 8
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Stark-shift measurements using emission spectroscopy are a powerful tool for advancing understanding in many plasma physics experiments. We use simultaneous two-dimensional space- and time-resolved spectra to study the electric field evolution in the 20 TW Particle Beam Fusion Accelerator II ion diode acceleration gap. Fiber optic arrays transport light from the gap to remote streaked spectrographs operated in a multiplexed mode that enables recording time-resolved spectra from eight spatial locations on a single instrument. Design optimization and characterization measurements of the multiplexed spectrograph properties include the astigmatism, resolution, dispersion, and sensitivity. A semiautomated line-fitting procedure determines the Stark shift and the related uncertainties. Fields up to 10 MV/cm are measured with an accuracy ±2%–4%. Detailed tests of the procedure confirm that the uncertainty in the wavelength-shift error bars is less than ±20%. Development of an active spectroscopy probe technique that uses laser-induced fluorescence from an injected atomic beam to obtain three-dimensional space- and time-resolved measurements of the electric and magnetic fields is in progress. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A review of the diagnostics used at Sandia National Laboratories to measure the parameters of intense lithium ion-beam hohlraum target experiments on Particle Beam Fusion Accelerator II will be presented. This diagnostic package contains an extensive suite of x-ray spectral and imaging diagnostics that enable measurements of target temperature and x-ray output. The x-ray diagnostics include time-integrated and time-resolved pinhole cameras, energy-resolved one-dimensional streaked imaging diagnostics, time-integrated and time-resolved grazing incidence spectrographs, a transmission grating spectrograph, an elliptical crystal spectrograph, a bolometer array, an 11- element x-ray diode array, and an 11-element PIN diode detector array. The incident Li beam symmetry and an estimate of incident Li beam power density can be measured from ion beam-induced characteristic x-ray line emission and neutron emission. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 10
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The heat capacity of crystalline zinc tris (thiourea) sulphate, has been measured in the range from 220 to 500 K by differential scanning calorimetry, and was found to obey the relationship Cp(T)=2.76×10−3 T+0.366 J g−1 K−1. Thermal expansion data have been measured in the range from 150 to 473 K. From these data, the principal thermal expansion coefficients were found to be α1=6.41×10−5 K−1, α2=4.52×10−5 K−1, and α3=−4.32×10−6 K−1. The thermal conductivity tensor of this orthorhombic crystal was calculated from values of the thermal diffusivity in the directions normal to the (100), (010), and (001) crystal planes by the laser flash method. The thermal conductivity coefficients at 295 K are k1=0.27 W m−1 K−1, k2=0.34 W m−1 K−1, and k3=0.54 W m−1 K−1. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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