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  • 1
    Electronic Resource
    Electronic Resource
    Nonlinear evolution of resistive tearing mode instability with shear flow and viscosity (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 376-387 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear evolution of the tearing mode instability with equilibrium shear flow is investigated via numerical solutions of the resistive magnetohydrodynamic (MHD) equations. The two-dimensional simulations are in slab geometry, are periodic in the x direction, and are initiated with solutions of the linearized MHD equations. The magnetic Reynolds number S was varied from 102 to 105, a parameter V that measures the strength of the flow in units of the average Alfvén speed was varied from 0 to 0.5, and the viscosity as measured by the Reynolds number Sν satisfied Sν≥103. When the shear flow is small (V≤0.3) the tearing mode saturates within one resistive time, while for larger flows the nonlinear saturation develops on a longer time scale. The two-dimensional spatial structure of both the flux function and the streamfunction distort in the direction of the equilibrium flow. The magnetic energy release decreases and the saturation time increases with V for both small and large resistivity. Shear flow decreases the saturated magnetic island width, and generates currents far from the tearing layer. The validity of the numerical solutions was tested by verifying that the total energy and the magnetic helicity are conserved. The results of the present study suggest that equilibrium shear flow may improve the confinment of tokamak plasma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860523
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  • 2
    Electronic Resource
    Electronic Resource
    Double tearing instability with shear flow (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2751-2757 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear evolution of the double tearing mode with parallel to the magnetic field equilibrium shear flow and viscosity is investigated numerically. Numerically obtained growth rates are found to agree with the solutions of the double tearing dispersion relation in the parameter range of validity. Solutions of the incompressible, time-dependent, linearized, viscoresistive magnetohydrodynamic equations for the double tearing mode with parallel flow are found for wide relevant parameter ranges. Large (weakly coupled) and small (strongly coupled) rational surface separation ys are investigated. The magnetic Reynolds number S is varied up to 108, and ambient flow velocities up to 0.57 of the Alfvén speed VA far from the tearing layer are considered. The normalized wave number α is 0.05 (long wavelength) and 0.5 (short wavelength). Spatial variations of the perturbed magnetic field ψ and flow W indicate the "nonconstant-ψ'' effects for small ys. Shear flow decouples the rational surfaces, reduces the growth rate, and transforms the instability to the standard tearing mode. Overstable modes are found from the solutions of the dispersion relation and in the numerical computations, and their frequencies are not affected by the value of viscosity. The temporal oscillations of the solutions increase with the flow at the resonant surfaces at a rate slower than that of the Doppler shift. For viscous Reynolds number Sv comparable to or larger than the magnetic Reynolds number a stabilizing effect was found, and in the presence of large flow the real growth rate γR scaling approaches the standard tearing mode scaling γR∼Sv1/6.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860148
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  • 3
    Electronic Resource
    Electronic Resource
    Resistive tearing mode instability with shear flow and viscosity (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1364-1373 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear theory of the resistive tearing mode instability in slab geometry, has been recently extended by introducing the effect of equilibrium shear flow and viscosity [Phys. Fluids 29, 2563 (1986); Phys. Fluids B 1, 2224 (1989); ibid. 2, 495 (1990); ibid. 2, 2575 (1990)]. In the present analysis, numerical solutions of the time-dependent resistive equations are generalized to this problem and growth rate scaling is obtained. The results of the computations are compared to previous work, and the computed growth rate scalings agree with analytical predictions. Namely, the "constant-ψ'' growth rate scales as S−1/2 and the "nonconstant-ψ'' growth rate scales as S−1/3, where S is the magnetic Reynolds number. The Furth–Killeen–Rosenbluth (FKR) scaling of S−3/5 is reproduced for small values of shear flow. The presence of flow introduces a new peak in the eigenfunction, which is outside of the peak that occurs in the case without flow. The introduction of viscosity and small shear alters the growth rate scaling to S−2/3(Sv/S)1/6 where Sv is the ratio of the viscous time to the Alfvén time. When the shear flow is large, the growth rate behaves in a more complex way, and Kelvin–Helmholtz instability effects are present.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859701
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic configurations for axisymmetric tandem mirror devices
    Amsterdam : Elsevier
    Computer Physics Communications 42 (1986), S. 217-232 
    Details
    ISSN: 0010-4655
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Computer Science , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0010-4655(86)90038-X
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  • 5
    Electronic Resource
    Electronic Resource
    SUMER Observations of the Evolution and the Disappearance of a Solar Prominence (1998)
    Springer
    Solar physics 183 (1998), S. 97-106 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The mechanisms that lead to the formation and the disappearance of prominences are poorly understood, at present. An arch-shaped prominence was observed with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on board the Solar and Heliospheric Observatory (SOHO) on 31 March–1 April 1996. The observations were performed at three wave-bands in the Lyman continuum. Ten successive images were obtained at 41-minute time intervals. Based on computed models of Gouttebroze, Heinzel, and Vial (1993), we have determined the temperature distribution of the prominence using the intensity ratio of 876 Å and 907 Å. The observed time sequence shows that parts of the prominence disappear possibly by heating, while other parts exhibit heating and cooling with apparent outward motion. We model the heat input with the linearized MHD equations using a prescribed initial density and a broad-band spectrum of Alfvén waves. We find a good qualitative agreement with observations. In the model the prominence is heated by the resonant absorption of Alfvén waves with frequencies that match the resonant condition for a particular flux tube structure that is determined by the magnetic field topology and plasma density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005052923972
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  • 6
    Electronic Resource
    Electronic Resource
    Soho Observations of Density Fluctuations in Coronal Holes (1999)
    Springer
    Space science reviews 87 (1999), S. 287-290 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In recent UVCS/SOHO White Light Channel (WLC) observations we found quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes at heliocentric distances of 1.9 to 2.45 solar radii. The motivation for the observation is the 2.5D MHD model of solar wind acceleration by nonlinear waves, that predicts compressive fluctuations in coronal holes. In February 1998 we performed new observations using the UVCS/WLC in the coronal hole and obtained additional data. The new data corroborate our earlier findings with higher statistical significance. The new longer observations show that the power spectrum peaks in the 10–12 minute range. These timescales agree with EIT observations of brightness fluctuations in polar plumes. We performed preliminary LASCO/C2 observations in an effort to further establish the coronal origin of the fluctuations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005181408719
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  • 7
    Electronic Resource
    Electronic Resource
    Two-fluid 2.5D MHD Simulations of the Fast Solar Wind in Coronal Holes and the Relation to UVCS Observations (1999)
    Springer
    Space science reviews 87 (1999), S. 165-168 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recent SOHO/UVCS observations indicate that the perpendicular proton and ion temperatures are much larger than electron temperatures. In the present study we simulate numerically the solar wind flow in a coronal hole with the two-fluid approach. We investigate the effects of electron and proton temperatures on the solar wind acceleration by nonlinear waves. In the model the nonlinear waves are generated by Alfvén waves with frequencies in the 10-3 Hz range, driven at the base of the coronal hole. The resulting electron and proton flow profile exhibits density and velocity fluctuations. The fluctuations may steepen into shocks as they propagate away from the sun. We calculate the effective proton temperature by combining the thermal and wave velocity of the protons, and find qualitative agreement with the proton kinetic temperature increase with height deduced from the UVCS Ly-α observations by Kohl et al. (1998).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005155209202
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