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  • 1
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    Modeling the effect of lithium-induced pedestal profiles on scrape-off-layer turbulence and the heat flux width (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-09-15
    Description: The effect of lithium (Li) wall coatings on scrape-off-layer (SOL) turbulence in the National Spherical Torus Experiment (NSTX) is modeled with the Lodestar SOLT ( SOL T urbulence) code. Specifically, the implications for the SOL heat flux width of experimentally observed, Li-induced changes in the pedestal profiles are considered. The SOLT code used in the modeling has been expanded recently to include ion temperature evolution and ion diamagnetic drift effects. This work focuses on two NSTX discharges occurring pre- and with-Li deposition. The simulation density and temperature profiles are constrained, inside the last closed flux surface only, to match those measured in the two experiments, and the resulting drift-interchange-driven turbulence is explored. The effect of Li enters the simulation only through the pedestal profile constraint: Li modifies the experimental density and temperature profiles in the pedestal, and these profiles affect the simulated SOL turbulence. The power entering the SOL measured in the experiments is matched in the simulations by adjusting “free” dissipation parameters (e.g., diffusion coefficients) that are not measured directly in the experiments. With power-matching, (a) the heat flux SOL width is smaller, as observed experimentally by infrared thermography and (b) the simulated density fluctuation amplitudes are reduced with Li, as inferred for the experiments as well from reflectometry analysis. The instabilities and saturation mechanisms that underlie the SOLT model equilibria are also discussed.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Turbulent transport regimes and the scrape-off layer heat flux width (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-04-29
    Description: Understanding the responsible mechanisms and resulting scaling of the scrape-off layer (SOL) heat flux width is important for predicting viable operating regimes in future tokamaks and for seeking possible mitigation schemes. In this paper, we present a qualitative and conceptual framework for understanding various regimes of edge/SOL turbulence and the role of turbulent transport as the mechanism for establishing the SOL heat flux width. Relevant considerations include the type and spectral characteristics of underlying instabilities, the location of the gradient drive relative to the SOL, the nonlinear saturation mechanism, and the parallel heat transport regime. We find a heat flux width scaling with major radius R that is generally positive, consistent with the previous findings [Connor et al. , Nucl. Fusion 39 , 169 (1999)]. The possible relationship of turbulence mechanisms to the neoclassical orbit width or heuristic drift mechanism in core energy confinement regimes known as low (L) mode and high (H) mode is considered, together with implications for the future experiments.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Mean flows and blob velocities in scrape-off layer (SOLT) simulations of an L-mode discharge on Alcator C-Mod (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-06-11
    Description: Two-dimensional scrape-off layer turbulence (SOLT) code simulations are compared with an L-mode discharge on the Alcator C-Mod tokamak [Greenwald et al ., Phys. Plasmas 21 , 110501 (2014)]. Density and temperature profiles for the simulations were obtained by smoothly fitting Thomson scattering and mirror Langmuir probe (MLP) data from the shot. Simulations differing in turbulence intensity were obtained by varying a dissipation parameter. Mean flow profiles and density fluctuation amplitudes are consistent with those measured by MLP in the experiment and with a Fourier space diagnostic designed to measure poloidal phase velocity. Blob velocities in the simulations were determined from the correlation function for density fluctuations, as in the analysis of gas-puff-imaging (GPI) blobs in the experiment. In the simulations , it was found that larger blobs moved poloidally with the E × B flow velocity, v E , in the near-SOL, while smaller fluctuations moved with the group velocity of the dominant linear (interchange) mode, v E  + 1/2 v di , where v di is the ion diamagnetic drift velocity. Comparisons are made with the measured GPI correlation velocity for the discharge. The saturation mechanisms operative in the simulation of the discharge are also discussed. It is found that neither sheared flow nor pressure gradient modification can be excluded as saturation mechanisms.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Secondary organic aerosol from diesel vs. gasoline [Environmental Sciences] (2012)
    National Academy of Sciences
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    Publication Date: 2012-11-08
    Description: Emissions from gasoline and diesel vehicles are predominant anthropogenic sources of reactive gas-phase organic carbon and key precursors to secondary organic aerosol (SOA) in urban areas. Their relative importance for aerosol formation is a controversial issue with implications for air quality control policy and public health. We characterize the chemical...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 5
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    Multiple Beam Two-Plasmon Decay: Linear Threshold to Nonlinear Saturation in Three Dimensions (2014)
    American Physical Society (APS)
    Details
    Publication Date: 2014-09-03
    Description: Author(s): J. Zhang, J. F. Myatt, R. W. Short, A. V. Maximov, H. X. Vu, D. F. DuBois, and D. A. Russell The linear stability of multiple coherent laser beams with respect to two-plasmon-decay instability in an inhomogeneous plasma in three dimensions has been determined. Cooperation between beams leads to absolute instability of long-wavelength decays, while shorter-wavelength shared waves are shown t... [Phys. Rev. Lett. 113, 105001] Published Tue Sep 02, 2014
    Keywords: Plasma and Beam Physics
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society (APS)
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  • 6
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    Cardiovascular evidence for an intermediate or higher metabolic rate in an ornithischian dinosaur (2000)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2000-04-25
    Description: Computerized tomography scans of a ferruginous concretion within the chest region of an ornithischian dinosaur reveal structures that are suggestive of a four-chambered heart and a single systemic aorta. The apparently derived condition of the cardiovascular system in turn suggests the existence of intermediate-to-high metabolic rates among dinosaurs.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Fisher, P E -- Russell, D A -- Stoskopf, M K -- Barrick, R E -- Hammer, M -- Kuzmitz, A A -- New York, N.Y. -- Science. 2000 Apr 21;288(5465):503-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Biomedical Imaging Facility, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough Street, Raleigh, NC 27606, USA. PaulvFisher@ncsu.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10775107" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Aorta/anatomy & histology ; Basal Metabolism ; Birds/anatomy & histology/metabolism ; Body Weight ; *Fossils ; Heart/*anatomy & histology/radiography ; Image Processing, Computer-Assisted ; Iron Compounds/analysis ; Minerals ; Paleontology ; Reptiles/*anatomy & histology/*metabolism ; Tomography Scanners, X-Ray Computed ; Tomography, X-Ray Computed ; X-Ray Diffraction
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    The Dinosaurs of' 47 (1991)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1991-02-15
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Russell, D A -- New York, N.Y. -- Science. 1991 Feb 15;251(4995):814.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17775461" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 8
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    Theory based scaling of edge turbulence and implications for the scrape-off layer width (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-11-02
    Description: Turbulence and plasma parameter data from the National Spherical Torus Experiment (NSTX) [Ono et al ., Nucl. Fusion 40 , 557 (2000)] is examined and interpreted based on various theoretical estimates. In particular, quantities of interest for assessing the role of turbulent transport on the midplane scrape-off layer heat flux width are assessed. Because most turbulence quantities exhibit large scatter and little scaling within a given operation mode, this paper focuses on length and time scales and dimensionless parameters between operational modes including Ohmic, low (L), and high (H) modes using a large NSTX edge turbulence database [Zweben et al ., Nucl. Fusion 55 , 093035 (2015)]. These are compared with theoretical estimates for drift and interchange rates, profile modification saturation levels, a resistive ballooning condition, and dimensionless parameters characterizing L and H mode conditions. It is argued that the underlying instability physics governing edge turbulence in different operational modes is, in fact, similar, and is consistent with curvature-driven drift ballooning. Saturation physics, however, is dependent on the operational mode. Five dimensionless parameters for drift-interchange turbulence are obtained and employed to assess the importance of turbulence in setting the scrape-off layer heat flux width λ q and its scaling. An explicit proportionality of the width λ q to the safety factor and major radius (qR) is obtained under these conditions. Quantitative estimates and reduced model numerical simulations suggest that the turbulence mechanism is not negligible in determining λ q in NSTX, at least for high plasma current discharges.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 9
    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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  • 10
    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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