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  • 1995-1999  (16)
  • 1990-1994  (11)
  • 1985-1989  (8)
  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-temperature-superconductor Josephson junctions with an edge geometry of superconductor/normal-metal/superconductor have been fabricated on yttria-stabilized zirconia substrates by engineering the electrode and N-layer material to reduce the lattice mismatches (a, b, and c). With GdBa2Cu3O7−δ as electrodes and Pr-doped Y0.6Pr0.4Ba2Cu3O7−δ as a barrier, the lattice mismatches from electrode and barrier layer are reduced to a very low level. The junctions fabricated with such a design demonstrate resistively shunted junction current-voltage characteristics under dc bias at temperatures in the range of 77–88 K. The quite low specific interface resistivity on the order of 10−10 Ω cm2 indicates that the junction performance is controlled by the normal-metal (N) layer material instead of the interfaces. The use of lattice-matched electrode and N-layer material is one of the key design rules to obtain controllable high-temperature superconductor Josephson junctions. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have performed aperture measurements and simulations for vacuum hohlraums heated by wire array implosions. A low-Z plastic coating is often applied to the aperture to create a high ablation pressure which retards the expansion of the gold hohlraum wall. However this interface is unstable and may be subject to the development of highly nonlinear perturbations ("jets") as a result of shocks converging near the edge of the aperture. These experiments have been simulated using Lagrangian and Eulerian radiation hydrodynamics codes. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3712-3713 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The strength of the magnetostrictive material, Terfenol-D, Tb0.27Dy0.73Fe2.0, has been evaluated by measuring the modulus of rupture as a function of the Fe stoichiometry of the compound. It is shown that the strength improves markedly as the Fe concentration decreases from the stoichiometric value of 2.0 in the compound. The increased strength results from the increasing volume fraction of the rare-earth metal phase produced in the Terfenol-D matrix by the solidification process at lower Fe concentrations.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 5057-5060 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The high-temperature superconductor YBa2Cu3O7−x has been irradiated in a transmission electron microscope to investigate the effect of high doses of ionizing energy on the microstructure of this material. Electrons of energies low enough to avoid knock-on displacement damage (80 and 100 keV) were used to achieve radiation doses of 1×1012 Gy at 115 K and 2×1013 Gy at room temperature. Using the criteria of twin fading and formation of extended defects, no microstructural damage was observed. These results indicate that YBa2Cu3O7−x is extremely resistant to damage by radiolytic processes.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2087-2090 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental results of enhanced interdiffusion of GaAs-AlGaAs interfaces are reported. These are obtained by implanting Ar ions at doses ranging from 2×1013 to 5×1014 cm−2 into heterostructure samples followed by rapid thermal annealing at 950 °C for 30 s. The degree of intermixing decreases from the surface up to the projected ion range and is a function of the implantation dose. It is postulated that this variation results from the coalescence of some of the excess vacancies into extended defects, which are then unavailable to assist in the enhanced interdiffusion process. By assuming that the concentration of mobile vacancies at any depth is proportional to the ion's electronic energy loss and inversely proportional to the ion's nuclear energy loss, the calculated intermixing results are shown to be in good agreement with the experimental data.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3448-3468 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of two-dimensional radiation magnetohydrodynamic calculations are presented of a Z-pinch implosion using a plasma flow switch. Results from a recent experiment using the high explosive driven generator Procyon, which delivered 16.5 MA to a plasma flow switch and switched about 15 MA into a static load, are used to study the implosion of a 29 mg load foil [J. H. Goforth et al., "Review of the Procyon Explosive Pulsed Power System,'' in Ninth IEEE Pulsed Power Conference, June 1993, Albuquerque, edited by K. R. Prestwich and W. L. Baker (Institute of Electrical and Electronics Engineers, Piscataway, NJ, 1993), p. 36]. The interaction of the switch with the load plasma and the effects of background plasma on the total radiation output is examined. Models which assume ideal switching are also included. Also included are the effects of perturbations in the load plasma which may be associated with initial vaporization of the load foil. If the background plasma density in the switch region and in the load region does not affect the dynamics, the pinch is predicted to produce a total radiation output of about 4 MJ. Including perturbations of the load plasma associated with switching and assuming a background plasma density after switching in excess of 10−7 g/cm3 results in a total output from the pinch of about 0.6 MJ. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1415-1429 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two-dimensional radiation magnetohydrodynamic simulations are presented that demonstrate the effects of magnetically driven Rayleigh–Taylor instabilities on the soft x-ray output from Z pinches. Instability models, which reproduce the current drive wave form and match visible framing camera data for instability wavelength and amplitude for implosions on capacitively driven inductive store systems, are used to study the structure of the x-ray output and the spectrum of radiation emitted from the pinch. The results indicate that standard magnetohydrodynamics is capable of reproducing much of the observed data when two-dimensional effects associated with Rayleigh–Taylor instabilities are included. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two-dimensional (2D) Eulerian radiation-magnetohydrodynamic code has been used to successfully simulate hollow metallic z-pinch experiments fielded on several facilities with a wide variety of drive conditions, time scales, and loads. The 2D simulations of these experiments reproduce important quantities of interest including the radiation pulse energy, power, and pulse width. This match is obtained through the use of an initial condition: the amplitude of a random density perturbation imposed on the initial plasma shell. The perturbations seed the development of magnetically driven Rayleigh–Taylor instabilities which greatly affect the dynamics of the implosion and the resulting production of radiation. Analysis of such simulations allows insights into the physical processes by which these calculations reproduce the experimental results. As examples, the insights gained from the simulations of Sandia "Z" accelerator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] experiments have allowed for the investigation of possible physical processes which produce high powers in "nested array" implosions and high temperatures within "dynamic hohlraum" loads. Building on these insights, the 2D code has been used in designing new experiments to optimize the desired physical conditions and in interpreting the experimental results obtained. These examples and others will be discussed as well as examples of simulation results where improvement is needed and what steps are being taken to make that improvement. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High wire number, 25-mm-diameter tungsten wire arrays have been imploded on the 8-MA Saturn generator [R. B. Spielman et al., AIP Conference Proceeding 195, 3 (American Institute of Physics, Woodbury, NY 1989)], operating in a long-pulse mode. By varying the mass of the arrays from 710 to 6140 μg/cm, implosion times of 130–250 ns have been obtained with implosion velocities of 50–25 cm/μs, respectively. These Z-pinch implosions produced plasmas with millimeter diameters that radiated 600–800 kJ of x-rays, with powers of 20–49 TW; the corresponding pulsewidths were 19–7.5 ns, with risetimes ranging from 6.5 to 4.0 ns. These powers and pulsewidths are similar to those achieved with 50-ns implosion times on Saturn. Two-dimensional, radiation-magnetohydrodynamic calculations indicate that the imploding shells in these long implosion time experiments are comparable in width to those in the short-pulse cases. This can be due to lower initial perturbations. A heuristic wire array model suggests that the reduced perturbations, in the long-pulse cases, may be due to the individual wire merger occurring well before the acceleration of the shell. The experiments and modeling suggest that 150–200 ns implosion time Z-pinches could be employed for high-power, x-ray source applications. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2605-2608 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reducing the length of 30 mm diam tungsten wire arrays on the 20 MA Z pulsed power accelerator [R. B. Spielman, S. F. Breeze, C. Deeney et al., Proceedings of the 11th International Conference on Particle Beams, Prague, Czech Republic, edited by K. Junwirth and J. Ullschmied (Czech Academy of Sciences, Prague, 1996), p. 150] from 2 to 0.75 cm has shown that the radiated powers are energies that remain constant at 170±30 TW and 1600±150 kJ. The length-independent nature of the power and energy results in the radiated power per unit length increasing from 85±10 to 240±30 TW/cm. These high-power densities should result in approximately a 20% increase in radiation temperatures produced by a Z-pinch-driven vacuum or internal hohlarums. Two-dimensional radiation magnetohydrodynamic calculations indicate that the constant radiated energies with varying pinch lengths is consistent with the energy input being due to the work done by the Lorentz forces during the radial collapse, resulting in kinetic energy and during the on-axis pinch phase, resulting in pdV or compressional heating. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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