2009 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/332

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Author: search.filters.author.Subramanian, KandaswamySubject: search.filters.subject.Shear dynamo

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    Shear dynamo problem: Quasilinear kinematic theory
    (2009-04-01) Sridhar, S.; Subramanian, Kandaswamy
    Large–scale dynamo action due to turbulence in the presence of a linear shear flow is studied. Our treatment is quasilinear and kinematic but is non perturbative in the shear strength. We derive the integro–differential equation for the evolution of the mean magnetic field, by systematic use of the shearing coordinate transformation and the Galilean invariance of the linear shear flow. For non helical turbulence the time evolution of the cross–shear components of the mean field do not depend on any other components excepting themselves. This is valid for any Galilean–invariant velocity field, independent of its dynamics. Hence the shear–current assisted dynamo is essentially absent, although large–scale non helical dynamo action is not ruled out.
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    Reconnecting Flux Rope Dynamo
    (2009-10-01) Subramanian, Kandaswamy; Baggaley, Andrew W; Barenghi, Carlo F.; et al.
    We develop a new model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multi-scale model of turbulence. Magnetic dissipation occurs only via reconnection of the flux ropes. This model can be viewed as an implementation of the asymptotic limit Rm → ∞ for a continuous magnetic field, where magnetic dissipation is strongly localized to small regions of strong field gradients. We investigate the kinetic energy release into heat, mediated by the dynamo action, both in our model and by solving the induction equation with the same flow. We find that a flux rope dynamo is an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy release in reconnections has a power-law form with the slope −3, consistent with the Solar corona heating by nanoflares.