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  • 1
    Electronic Resource
    Electronic Resource
    Theoretical and experimental studies of CO2 laser evaporation of clouds (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4601-4616 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A study of the effects of laser radiation on cloud drops and of the possibility of producing a clear optical channel in a cloud is presented. In order to produce a model that is appropriate to a realistic cloud with a distribution of drop sizes it is first necessary to study what happens to a single water drop subjected to laser radiation of different intensities. Various heating regimes are mapped out as a function of laser flux and fluence at the 10.6 μm wavelength. It is found that typical cloud drops can superheat until they become unstable and explode from the center. For a long laser pulse the boundary for this to occur is found to be 50(5/r)2 kW/cm2, where r is the drop radius in microns. Using these results a model that is spatially one-dimensional through the cloud is constructed for a distribution of drop sizes. Laser beam intensity as the light penetrates a cloud is calculated from Mie scattering and absorption cross sections for a beam diameter that is small in the sense that light scattered once is assumed lost. The internal temperature distribution of the drops is calculated and a phenomenological drop explosion model is given for drops that reach the unstable 305 °C spinodal temperature at their center. Energy and water mass content are conserved as the cloud background is modified in an average sense by drop evaporation or recondensation. Recondensation is treated in the diffusion regime according to the Kohler model, with vapor pressure over a drop modified by surface tension and dissolved nonwater content. Comparison with experimental data for a laboratory produced cloud is given and good agreement, particularly with respect to the predicted onset of drop explosion, is found. Results are also presented for hypothetical cloud conditions and laser intensities. The possibility of clearing a thin cloud with low fluence to the 3.8 μm is considered, as well as the passive evaporation of melted ice crystal clouds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349097
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  • 2
    Electronic Resource
    Electronic Resource
    Two-dimensional kinetic field-reversed equilibria (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1026-1040 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two-dimensional kinetic description of field-reversed equilibria has been developed. Three equilibrium models are presented: a kinetic model, a rigidly rotating model, and a magnetohydrodynamics (MHD) model. The kinetic model of equilibrium provides spatial distributions of the macroscopic moments, including velocity shear, that are in good agreement with experimental observations. The rigidly rotating and MHD models allow more general pressure profiles than previous studies. These models, which allow the computation of a wide range of equilibria, suggest that for parameters typical of the current experiments kinetic modifications of the equilibrium are small; however, they may be important if the field-reversed configuration is interacting strongly with a magnetic mirror. Also, the ability to compute kinetic equilibria makes possible a self-consistent examination of the stability of field-reversed configurations, which is believed to be strongly influenced by kinetic effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859831
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  • 3
    Electronic Resource
    Electronic Resource
    Flux confinement measurements in large field-reversed configuration equilibria (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1706-1708 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The poloidal magnetic flux φ in large field-reversed configuration plasmas is examined experimentally. A wide range of initial equilibrium conditions, with 1≤φ≤8 mWb, is produced by varying the reverse bias magnetic field strength. The flux confinement time τφ at first improves with bias, albeit with field-null resistivities an order of magnitude larger than classical. A further increase in bias results in a reduction of τφ, which is inconsistent with either classical or anomalous diffusion theory. The data suggest the importance of nondiffusive processes such as instabilities or formation dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859443
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  • 4
    Electronic Resource
    Electronic Resource
    Nonlinear magnetohydrodynamic studies of the tilt mode in field-reversed configurations (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1225-1232 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A three-dimensional magnetohydrodynamic code has been used to study the nonlinear evolution of the tilt instability in a field-reversed configuration. The evolution of the mode has been followed through magnetic field reconnection to complete the loss of confinement, with no evidence of any nonlinear stabilizing effects. The influence of plasma rotation has also been investigated. It was found that while the mode remains unstable, its character changed at high rotation rates. It evolves from an internal mode with a very small displacement velocity at the separatrix, to an external mode with almost no radial component to the displacement velocity. Hall term effects were found to be capable of reducing the growth rate for small and elongated configurations, but again, a change in mode character was found to prevent the stabilization predicted in a previous analysis. Kinetic effects remain the most promising mechanism to explain the observed stability of current experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858998
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