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  1. Taking a fresh look at boiling heat transfer on the road to improved nuclear economics and efficiency

    Pointer, William David ; Baglietto, Emilio - Nuclear Espana (1996)
    Here, in the effort to reinvigorate innovation in the way we design, build, and operate the nuclear power generating stations of today and tomorrow, nothing can be taken for granted. Not even the seemingly familiar physics of boiling water. The Consortium for the Advanced Simulation of Light Water Reactors, or CASL, is focused on the deployment of advanced modeling and simulation capabilities to enable the nuclear industry to reduce uncertainties in the prediction of multi-physics phenomena and continue to improve the performance of today’s Light Water Reactors and their fuel. An important part of the CASL mission is the developmentmore » of a next generation thermal hydraulics simulation capability, integrating the history of engineering models based on experimental experience with the computing technology of the future.« less

  2. DShaper: An approach for handling missing low-Q data in pair distribution function analysis of nanostructured systems

    Olds, Daniel ; Wang, Hsiu -Wen ; Page, Katharine L. - Journal of Applied Crystallography (Online)
    In this work we discuss the potential problems and currently available solutions in modeling powder-diffraction based pair-distribution function (PDF) data from systems where morphological feature information content includes distances in the nanometer length scale, such as finite nanoparticles, nanoporous networks, and nanoscale precipitates in bulk materials. The implications of an experimental finite minimum Q-value are addressed by simulation, which also demonstrates the advantages of combining PDF data with small angle scattering data (SAS). In addition, we introduce a simple Fortran90 code, DShaper, which may be incorporated into PDF data fitting routines in order to approximate the so-called shape-function for anymore » atomistic model.« less

  3. Intrinsic torque reversals induced by magnetic shear effects on the turbulence spectrum in tokamak plasmas

    Lu, Z. X. ; Wang, W. X. ; Diamond, P. H. ; ... - Physics of Plasmas
    We report that intrinsic torque, which can be generated by turbulent stresses, can induce toroidal rotation in a tokamak plasma at rest without direct momentum injection. Reversals in intrinsic torque have been inferred from the observation of toroidal velocity changes in recent lower hybrid current drive (LHCD) experiments. Here we focus on understanding the cause of LHCD-induced intrinsic torque reversal using gyrokinetic simulations and theoretical analyses. A new mechanism for the intrinsic torque reversal linked to magnetic shear (sˆ) effects on the turbulence spectrum is identified. This reversal is a consequence of the ballooning structure at weak sˆ . Basedmore » on realistic profiles from the Alcator C-Mod LHCD experiments, simulations demonstrate that the intrinsic torque reverses for weak sˆ discharges and that the value of sˆ crit is consistent with the experimental results sˆ expcrit [Rice et al., Phys. Rev. Lett. 111, 125003 (2013)]. In conclusion, the consideration of this intrinsic torque feature in our work is important for the understanding of rotation profile generation at weak and its consequent impact on macro-instability stabilization and micro-turbulence reduction, which is crucial for ITER. It is also relevant to internal transport barrier formation at negative or weakly positive sˆ .« less

  4. Assessment of uncertainties in the response of the African monsoon precipitation to land use change simulated by a regional model

    Hagos, Samson M. ; Leung, Lai-Yung Ruby ; Xue, Yongkang ; ... - Climate Dynamics
    Land use and land cover over Africa have changed substantially over the last sixty years and this change has been proposed to affect monsoon circulation and precipitation. This study examines the uncertainties on the effect of these changes on the African Monsoon system and Sahel precipitation using an ensemble of regional model simulations with different combinations of land surface and cumulus parameterization schemes. Furthermore, the magnitude of the response covers a broad range of values, most of the simulations show a decline in Sahel precipitation due to the expansion of pasture and croplands at the expense of trees and shrubsmore » and an increase in surface air temperature.« less

  5. Linear fixed-field multipass arcs for recirculating linear accelerators

    Morozov, V. S. ; Bogacz, S. A. ; Roblin, Y. R. ; ... - Physical Review Special Topics. Accelerators and Beams

  6. Spatially resolved distribution function and the medium-range order in metallic liquid and glass

    Fang, Xiaowei ; Wang, Cai-Zhuang ; Hao, Shaogang ; ... - Scientific Reports
    The structural description of disordered systems has been a longstanding challenge in physical science. We propose an atomic cluster alignment method to reveal the development of three-dimensional topological ordering in a metallic liquid as it undercools to form a glass. By analyzing molecular dynamic (MD) simulation trajectories of a Cu64.5Zr35.5 alloy, we show that medium-range order (MRO) develops in the liquid as it approaches the glass transition. Specifically, around Cu sites, we observe 'Bergman triacontahedron' packing (icosahedron, dodecahedron and icosahedron) that extends out to the fourth shell, forming an interpenetrating backbone network in the glass. The discovery of Bergman-type MROmore » from our order-mining technique provides unique insights into the topological ordering near the glass transition and the relationship between metallic glasses and quasicrystals.« less

  7. Forward-backward asymmetry in top quark-antiquark production

    Abazov, Victor Mukhamedovich - Physical Review. D, Particles, Fields, Gravitation and Cosmology
    We present a measurement of forward-backward asymmetry in top quark-antiquark production in proton-antiproton collisions in the final state containing a lepton and at least four jets. Using a dataset corresponding to an integrated luminosity of 5.4 fb-1, collected by the D0 experiment at the Fermilab Tevatron Collider, we measure the t{bar t} forward-backward asymmetry to be (9.2 ± 3.7)% at the reconstruction level. When corrected for detector acceptance and resolution, the asymmetry is found to be (19.6 ± 6.5)%. We also measure a corrected asymmetry based on the lepton from a top quark decay, found to be (15.2 ± 4.0)%.more » The results are compared to predictions based on the next-to-leading-order QCD generator mc@nlo. The sensitivity of the measured and predicted asymmetries to the modeling of gluon radiation is discussed.« less

  8. Future Challenges for Nuclear Data Research in Fission

    Chadwick, Mark B. - Journal of the Korean Physical Society
    I describe some high priority research areas in nuclear fission, where applications in nuclear reactor technologies and in modeling criticality in general are demanding higher accuracies in our databases. Here, we focus on fission cross sections, fission neutron spectra, and fission product data.

  9. Coupling impedance and wake functions for laminated structures with an application to the Fermilab Booster

    Macridin, Alexandru ; Spentzouris, Panagiotis ; Amundson, James ; ... - Physical Review Special Topics - Accelerators and Beams

  10. Structural Analysis of the SHMS Cosine Theta Superconducting Dipole Force Collar

    Lassiter, Steven ; Brindza, Paul ; Fowler, Mike ; ... - IEEE Transactions on Applied Superconductivity
    Jefferson Laboratory is developing a set of innovative superconducting magnets for the 12 GeV upgrade in JLAB Hall C. Here, we will report on the finite element analysis (FEA) of the force collar for the Super High Momentum Spectrometer Cosine Theta Dipole magnet. The force collar is designed with an interference fit and intended to provide enough pressure after cool down to operating temperature to counteract Lorentz forces acting on the dipole coil during operation. By counteracting the Lorentz forces and keeping the coil pack in overall compression, movement of the coils is expected to be minimized. The dimensional geometrymore » of the cold mass is maintained in the commercial solid modeling code UG/I-DEAS while the magnetic field design is maintained in the commercial TOSCA code from Vector Fields. The three dimensional FEA was conducted in the commercial codes ANSYS and IDEAS. The method for converting the models and calculating the loads transferred to the structure is discussed. The results show the cold mass response to: force collar assembly preload, differential thermal contraction, and operational Lorentz loads. Evaluations are made for two candidate force collar materials and two candidate force collar designs.« less
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