Search Results - (Author, Cooperation:A. R. Bell)

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  1. 1
    Staff View
    Publication Date:
    2012-01-28
    Publisher:
    Nature Publishing Group (NPG)
    Print ISSN:
    0028-0836
    Electronic ISSN:
    1476-4687
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Published by:
    http://www.nature.com/

    Latest Papers from Table of Contents or Articles in Press
  2. 2
    Beg, F. N. ; Bell, A. R. ; Dangor, A. E. ; Danson, C. N. ; Fews, A. P. ; Glinsky, M. E. ; Hammel, B. A. ; Lee, P. ; Norreys, P. A. ; Tatarakis, M.

    [S.l.] : American Institute of Physics (AIP)
    Published 1997
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The interaction of a 1053 nm picosecond laser pulse with a solid target has been studied for focused intensities of up to 1019 W cm−2. The maximum ion energy cutoff Emax (which is related to the hot electron temperature) is in the range 1.0–12.0 MeV and is shown to scale as Emax(approximate)I1/3. The hot electron temperatures were in the range 70–400 keV for intensities up to 5×1018 W cm−2 with an indication of a high absorption of laser energy. Measurements of x-ray/γ-ray bremsstrahlung emission suggest the existence of at least two electron temperatures. Collimation of the plasma flow has been observed by optical probing techniques. © 1997 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.872103

    Articles: DFG German National Licenses
  3. 3
    Bell, A. R.

    [S.l.] : American Institute of Physics (AIP)
    Published 1994
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    In a series of three idealized magnetohydrodynamic (MHD) calculations in cylindrical geometry, we show that an azimuthal magnetic field can produce well-collimated jets by the pinch effect. In a laser-produced plasma, the magnetic field is generated by crossed density and temperature gradients (∇n×∇T), and may be responsible for the "imprint problem.'' In an astrophysical plasma, differential rotation associated with an accretion disk can generate the magnetic field, which may then be responsible for jet formation on stellar and galactic scales.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.870666

    Articles: DFG German National Licenses
  4. 4
    Zdravkovic, D. ; Coppins, M. ; Bell, A. R.

    [S.l.] : American Institute of Physics (AIP)
    Published 2001
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The effect of radial dynamics on the ideal magnetohydrodynamic (MHD) linear m=0 instability in diffuse profile Z pinches is investigated with a two-dimensional (2D) MHD code. The radial dynamics impose a periodic behavior within which three distinct phases of instability development can be distinguished. The comparison with the Rayleigh–Taylor instability is presented. The behavior is best characterized as MHD instability enhanced by the radial dynamics. © 2001 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.1337617

    Articles: DFG German National Licenses
  5. 5
    Ersfeld, B. ; Bell, A. R.

    [S.l.] : American Institute of Physics (AIP)
    Published 2000
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The influence of the shape of the electron velocity distribution on collisional absorption of laser irradiation in a plasma is considered, describing its self-consistent evolution by a Boltzmann equation, and treating collisions with (immobile) ions and among electrons in Fokker–Planck approximation. In order to facilitate numerical solutions for intensities where the distribution is displaced by several times its width it is approximated as isotropic in a reference frame moving with the average electron velocity. In the limit of high ion charges the resulting non-Maxwellian radial shape fairly reproduces those features of the complete solution relevant for absorption. For singly charged ions the shape is closer to Maxwellian, as expected, but the remaining differences still affect the absorption. For low collision frequency, averaging over the laser time scale yields a generalization of Langdon's analysis for low intensities [Phys. Rev. Lett. 44, 575 (1980)]. © 2000 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.873899

    Articles: DFG German National Licenses
  6. 6
    Chittenden, J. P. ; Aliaga Rossel, R. ; Lebedev, S. V. ; Mitchell, I. H. ; Tatarakis, M. ; Bell, A. R. ; Haines, M. G.

    [S.l.] : American Institute of Physics (AIP)
    Published 1997
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    A two-dimensional magneto-hydrodynamic simulation incorporating cold start conditions is used to explain the early phase of carbon fiber Z-pinch experiments. The rapid development of large scale, nonlinear m=0 perturbations in the plasma corona is reproduced. X-ray bright spot formation in the necks of the instability is followed by bright spot bifurcation and fast axial motion. Bright spot bifurcation is found to be due to axial components of the j×B force and occurs off-axis due to the presence of a residual core of unionized carbon. Artificial diagnostic images are generated from the simulations data to allow direct comparison with experimental x-ray imaging and laser probing diagnostics. The accurate reproduction of the experimental images provides confirmation that the experimentally observed features are a repercussion of the non-linear development of the m=0 instability in an ionizing medium. © 1997 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.872593

    Articles: DFG German National Licenses
  7. 7
    Bell, A. R.

    [S.l.] : American Institute of Physics (AIP)
    Published 1985
    Staff View
    ISSN:
    1089-7666
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Electron energy transport in a laser-produced ablating plasma is modeled by the Vlasov–Fokker–Planck equation for electrons and the fluid equations for cold ions. These equations are solved using approximations which maintain good accuracy but allow faster computational solution than was previously possible. It is found that the spatial profiles for temperature and density in planar geometry differ very little from those calculated from the Spitzer conductivity. At high laser intensities, the plasma flow diverges as it flows away from the solid target and the effects of nonplanar flow are important. This is modeled by the adoption of spherical geometry, and it is found that the Spitzer conductivity breaks down and the temperature and density profiles differ significantly from those calculated using the Spitzer conductivity.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.865378

    Articles: DFG German National Licenses
  8. 8
    BELL, A. R. ; GULL, S. F. ; KENDERDINE, S.

    [s.l.] : Nature Publishing Group
    Published 1975
    Staff View
    ISSN:
    1476-4687
    Source:
    Nature Archives 1869 - 2009
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Notes:
    [Auszug] During November 1974, Cas A was observed with the Cambridge 5-km telescope4 at a frequency of 5 GHz, giving half-power beamwidths of 2" in right ascension and 2.3" in declination. A total of 128 interferometer spacings were used, so that the synthesised beamshape has its first grating response at ...
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1038/257463a0

    Articles: DFG German National Licenses
  9. 9
    Bell, A. R.

    [s.l.] : Nature Publishing Group
    Published 1990
    Staff View
    ISSN:
    1476-4687
    Source:
    Nature Archives 1869 - 2009
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1038/345136a0

    Articles: DFG German National Licenses
  10. 10
    Bell, A. R.

    [s.l.] : Nature Publishing Group
    Published 1989
    Staff View
    ISSN:
    1476-4687
    Source:
    Nature Archives 1869 - 2009
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Notes:
    [Auszug] THE diversity of nonlinear interactions involving waves in plasmas is both a fascination and a frustration to plasma physicists. Often the interactions arise unexpectedly to frustrate attempts to design useful plasma devices, but the very wealth of interactions gives great scope for inventive ...
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1038/341026a0

    Articles: DFG German National Licenses
  11. 11
    Savopulos, M. ; Quenby, J. J. ; Bell, A. R.
    Springer
    Published 1995
    Staff View
    ISSN:
    1573-093X
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Physics
    Notes:
    Abstract A new method for solving the transport equation and boundary condition describing diffusive shock acceleration for interplanetary corotating interaction regions is provided. It involves inverting a quindiagonal matrix. Application of this method to realistic parameters indicates that the parallel diffusion coefficient magnitude is critical in determining whether observed particle distribution functions are exponential or power law.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00680626

    Articles: DFG German National Licenses