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  • 1
    Electronic Resource
    Electronic Resource
    High-power high-frequency-induced Langmuir turbulence in the smooth ionosphere at Arecibo. I. Theoretical predictions for altitude-resolved plasma line radar spectra (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 791-801 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This is the first of two papers comprising a theoretical and observational study of new, altitude-resolved, observations at Arecibo of Langmuir turbulence induced in the ionosphere by a powerful high-frequency (hf) heater operated at very low duty cycles. As shown in paper II [Cheung et al., Phys. Plasmas 8, 802 (2001)], higher power enabled the first observation at Arecibo of the well-developed decay-cascade features in the Thomson scatter radar power spectrum at the unmodified matching altitudes. New theoretical predictions are presented here for the parameters of these observations emphasizing the altitude and pump power dependence of the radar spectra and the time dependence of the spectra from the decaying spectra following heater switch-off. Further details of the strong turbulence signatures from higher altitudes are also presented. At the lower matching altitudes the increase, with hf power, of the angular width of the well-developed decay-cascade spectrum allows these spectral features to come into the view of the Arecibo radar. The favorable comparison of the simulation predictions and observations is discussed in the second paper. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1345703
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  • 2
    Electronic Resource
    Electronic Resource
    The Enigma of the Extinction of the Dinosaurs (1979)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Earth and Planetary Sciences 7 (1979), S. 163-182 
    Details
    ISSN: 0084-6597
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ea.07.050179.001115
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  • 3
    Electronic Resource
    Electronic Resource
    Flow Lasers (1975)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 7 (1975), S. 115-139 
    Details
    ISSN: 0066-4189
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.fl.07.010175.000555
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  • 4
    Electronic Resource
    Electronic Resource
    A quasilinear, Fokker–Planck description of fast wave minority heating permitting off-axis tangency interactions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 52-63 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The off-axis quasilinear fast wave minority heating description of Catto and Myra [Phys. Fluids B 4, 187 (1992)] has been improved and implemented in a code which solves the combined quasilinear and collision operator equation for the minority distribution function. Geometrical complications of a minority resonance nearly tangent to a flux surface in the presence of trapped as well as passing particles are retained. The tangency interactions alter the moments and the fusion reaction rate parameter in a model which explores heating on a single flux surface. The strong tangency interactions enhance the more familiar interactions due to trapped particles turning in the vicinity of the minority resonance. An asymmetry in off-axis heating effects occurs because heating on the low field side of the magnetic axis heats more trapped particles than high field side heating. This asymmetry is responsible for the better performance of the low field side case relative to the high and on-axis cases and provides some control over the power absorbed by and the energy stored in the trapped particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870558
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  • 5
    Electronic Resource
    Electronic Resource
    Coaxial mode excitation and dissipation in ion Bernstein wave experiments (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 283-294 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In recent ion Bernstein wave (IBW) heating experiments on the Tokamak Fusion Test Reactor (TFTR) [J. R. Wilson. R. E. Bell, S. Bernabei, K. Hill et al., Phys. Plasmas 5, 1721 (1998)] a velocity shear layer in the plasma core was obtained. The magnitude of velocity shear was believed to be too small to create an internal transport barrier, because of parasitic edge processes which reduced the power coupled to the core. In this paper we investigate these rf (radio frequency) edge processes by employing a model which includes both coaxial modes and their dissipation in rf plasma sheaths. The coaxial mode (here, an electron plasma wave trapped in the halo plasma between the lower hybrid layer and the vessel wall) can propagate at low poloidal wave numbers. This feature is shown to relate to the observed poloidal phasing dependence of the antenna loading. Results of analytical models and a three-dimensional antenna code are presented. The experimentally observed loading is also nonlinear, being larger at very low powers. This feature is explored using an rf sheath dissipation model. Loading into the coaxial mode is expected to maximize when the density gradient at the lower hybrid layer is steep, preventing efficient mode transformation to the IBW. The role of ponderomotive force in modifying the density profile is also discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873798
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  • 6
    Electronic Resource
    Electronic Resource
    Role of ponderomotive density expulsion in ion Bernstein wave coupling to the core plasma (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 743-751 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When the density at the ion Bernstein wave (IBW) antenna is relatively low, mode transformation of the electron plasma wave to the IBW is sensitive to the density gradient scale length, and hence to ponderomotive effects. A second-order nonlinear ordinary differential equation that describes mode transformation at the lower-hybrid layer, including self-consistent ponderomotive density profile modification, is solved for the rf electrostatic potential in front of the IBW antenna, for the particular case of heating just below the second harmonic of the deuterium cyclotron frequency. The complex antenna impedance and a local reflectivity are calculated, assuming vacuum within the antenna box. These calculations reveal diminished antenna coupling to the IBW with increasing ponderomotive density expulsion, as compared to the linear prediction. The ponderomotive force increases the density gradient in the edge plasma, thus enhancing reflection and lowering the loading resistance. The model also describes the direct launch of IBWs in high edge density regimes, lacking a lower-hybrid layer, where the impedance is found to be much smaller than in the low density regime. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872772
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  • 7
    Electronic Resource
    Electronic Resource
    Recent Trident single hot spot experiments: Evidence for kinetic effects, and observation of Langmuir decay instability cascade : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 2311-2320 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single hot spot experiments offer several unique opportunities for developing a quantitative understanding of laser-plasma instabilities. These include the ability to perform direct numerical simulations of the experiment due to the finite interaction volume, isolation of instabilities due to the nearly ideal laser intensity distribution, and observation of fine structure due to the homogeneous plasma initial conditions. Experiments performed at Trident in the single hot spot regime have focused on the following issues. First, the intensity scaling of stimulated Raman scattering (SRS) for classically large damping regimes (kλD=0.35) was examined, and compared to classical SRS theory. SRS onset was observed at intensities much lower than expected (2×1015 W/cm2), from which nonclassical damping is inferred. Second, Thomson scattering was used to probe plasma waves driven by SRS, and structure was observed in the scattered spectra consistent with multiple steps of the Langmuir decay instability. Finally, scattering from a plasma wave was observed whose frequency and phase velocity are between an ion acoustic wave and an electron plasma wave. The presence of this wave cannot be explained by linear Landau theory, and it is shown to be consistent with a BGK-type mode due to electron trapping. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1468857
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  • 8
    Electronic Resource
    Electronic Resource
    Scattering of radiation by alpha particle induced fluctuations : Eighth topical conference on high−temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3211-3213 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Motivated by the possibility of diagnosing alpha particles in a burning fusion plasma by scattering radiation off of the fluctuations that they induce, we model the linear Maxwell–Vlasov theory of the scattering in a homogeneous plasma consisting of electrons, deuterium ions, and alpha particles. The fluctuating electric field is driven by the undressed particle current so that the problem of finding the power spectrum of the scattered radiation amounts to solving a system of linear algebraic equations "driven'' by the power spectrum of the undressed current density fluctuations; a coefficient matrix contains the dielectric tensor. Scattering off of field fluctuations is included in the model in addition to the usual scattering off of electron density fluctuations. The model is solved numerically and we compare our results to earlier studies that neglected scattering off field fluctuations and assumed electrostatic shielding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141636
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  • 9
    Electronic Resource
    Electronic Resource
    Running Dinosaurs (1976)
    [s.l.] : Nature Publishing Group
    Nature 264 (1976), S. 486-486 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] ALEXANDER'S1 use of stride length and footprint size to determine from trackways the speed of terrestrial vertebrates will greatly increase our understanding of dinosaurian behaviour. None of the trackways he cited were of large running dinosaurs, although he did not suggest that large dinosaurs ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/264486a0
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  • 10
    Electronic Resource
    Electronic Resource
    Fossil charcoal and the palaeoatmosphere (1981)
    [s.l.] : Nature Publishing Group
    Nature 290 (1981), S. 428-428 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] IT has been proposed by Cope and Chaloner1 that oxygen levels in palaeoatmospheres may be assessed by the presence or absence of charcoal in the geological record. Although oxygen is required for burning, it is not necessary for charcoal formation. When wood is subjected to high temperatures, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/290428a0
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