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End date: 2009 Ă— Start date: 2000 Ă— search.filters.applied.f.series: New Journal of Physics 9 (2007) Ă— WGL Institute: AIP Ă—

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Now showing 1 - 3 of 3
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    Shell models for Hall effect induced magnetic turbulence
    (College Park, MD : Institute of Physics Publishing, 2007) Frick, P.; Stepanov, R.; Rheinhardt, M.
    The Hall effect occurs in strongly magnetized conductive media and results in non-dissipative currents perpendicular to the electric field. We discuss its influence on the magnetic field dynamics ignoring fluid motion and ambipolar diffusion. The magnetic field evolution can then be basically similar to that of the velocity field in hydrodynamic turbulence resulting in a magnetic turbulence. Shell models for the induction equation with Hall effect are constructed on the basis of the conservation of magnetic energy and helicity in the dissipation-free limit. Numerical simulations of these models indicate that a magnetic energy cascade does occur, but the time behaviour and spatial spectrum of the magnetic field are very different from those of the velocity in shell models of hydrodynamic turbulence. ©IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
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    Structure and stability of the magnetic solar tachocline
    (College Park, MD : Institute of Physics Publishing, 2007) RĂ¼diger, G.; Kitchatinov, L.L.
    Rather weak fossil magnetic fields in the radiative core can produce the solar tachocline if the field is almost horizontal in the tachocline region, i.e. if the field is confined within the core. This particular field geometry is shown to result from a shallow (≲1 Mm) penetration of the meridional flow existing in the convection zone into the radiative core. Two conditions are thus crucial for a magnetic tachocline theory: (i) the presence of meridional flow of a few metres per second at the base of the convection zone, and (ii) a magnetic diffusivity inside the tachocline smaller than 108 cm 2 s-1. Numerical solutions for the confined poloidal fields and the resulting tachocline structures are presented. We find that the tachocline thickness runs as Bp-1/2 with the poloidal field amplitude falling below 5% of the solar radius for Bp > 5 mG. The resulting toroidal field amplitude inside the tachocline of about 100 G does not depend on the Bp. The hydromagnetic stability of the tachocline is only briefly discussed. For the hydrodynamic stability of latitudinal differential rotation we found that the critical 29% of the 2D theory of Watson (1981 Geophys. Astrophys. Fluid Dyn. 16 285) are reduced to only 21% in 3D for marginal modes of about 6 Mm radial scale. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
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    Experiments on the magnetorotational instability in helical magnetic fields
    (College Park, MD : Institute of Physics Publishing, 2007) Stefani, F.; Gundrum, T.; Gerbeth, G.; RĂ¼diger, G.; Szklarski, J.; Hollerbach, R.
    The magnetorotational instability (MRI) plays a key role in the formation of stars and black holes, by enabling outward angular momentum transport in accretion discs. The use of combined axial and azimuthal magnetic fields allows the investigation of this effect in liquid metal flows at moderate Reynolds and Hartmann numbers. A variety of experimental results is presented showing evidence for the occurrence of the MRI in a Taylor-Couette flow using the liquid metal alloy GaInSn. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.