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LargeScale Dynamos and Magnetic Helicity: Principles
"... Dynamos are studied by astrophysical, planetary, and fusion communities but the differences between dynamo types can be a source of confusion. To elucidate the relationship between the different dynamos, I divide dynamos into three categories e.g. [1]: 1. Nonhelical flowdriven dynamos which amplify ..."
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amplify fields on scales at or below the driving turbulence; 2. Helical flowdriven dynamos which amplify or sustain large scale magnetic fields in an otherwise turbulent flow. Traditional stellar, planetary, and Galactic dynamos aimed at explaining cycle periods and largescale fields fit
Laboratory Plasma Dynamos, Astrophysical Dynamos, and Magnetic Helicity Evolution
, 2006
"... The term “dynamo ” means different things to the laboratory fusion plasma and astrophysical plasma communities. To alleviate the resulting confusion and to facilitate interdisciplinary progress, we pinpoint conceptual differences and similarities between laboratory plasma dynamos and astrophysical d ..."
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dynamos. We can divide dynamos into three types: 1. magnetically dominated helical dynamos which sustain a large scale magnetic field against resistive decay and drive the magnetic geometry toward the lowest energy state, 2. flowdriven helical dynamos which amplify or sustain large scale magnetic fields
Magnetic Helicity Conservation and Astrophysical Dynamos
 Astrophys. J
"... We construct a magnetic helicity conserving dynamo theory which incorporates a calculated magnetic helicity current. In this model the fluid helicity plays a small role in large scale magnetic field generation. Instead, the dynamo process is dominated by a new quantity, derived from asymmetries in t ..."
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Cited by 15 (0 self)
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We construct a magnetic helicity conserving dynamo theory which incorporates a calculated magnetic helicity current. In this model the fluid helicity plays a small role in large scale magnetic field generation. Instead, the dynamo process is dominated by a new quantity, derived from asymmetries
DYNAMO ACTION IN STEADY HELICAL PIPE FLOW
"... Summary The steady, pressuredriven flow of a conducting fluid down a helical pipe of rectangular crosssection is shown to drive a kinematic dynamo at moderate values of the magnetic Reynolds number, R m . The asymptotic structure of the growing modes is analysed as Rm → ∞. This is the first lamin ..."
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Summary The steady, pressuredriven flow of a conducting fluid down a helical pipe of rectangular crosssection is shown to drive a kinematic dynamo at moderate values of the magnetic Reynolds number, R m . The asymptotic structure of the growing modes is analysed as Rm → ∞. This is the first
Turbulent dynamos with advective magnetic helicity flux
, 2012
"... Many astrophysical bodies harbor magnetic fields that are thought to be sustained by a dynamo process. However, it has been argued that the production of largescale magnetic fields by meanfield dynamo action is strongly suppressed at large magnetic Reynolds numbers owing to the conservation of mag ..."
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Cited by 3 (0 self)
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–diffusive fluxes of magnetic helicity in the dynamo. In particular, we study how the dynamo is affected by advection. We do this by performing direct numerical simulations of a turbulent dynamo of α 2 type driven by forced turbulence in a Cartesian domain in the presence of a flow toward the upper and lower
Magnetic helicity in galactic dynamos
, 2008
"... Abstract. Magnetic fields correlated on kiloparsec scales are seen in spiral galaxies. Their origin could be due to amplification of a small seed field by a turbulent galactic dynamo. We review the current status of the galactic dynamo, especially the constraints imposed by magnetic helicity conserv ..."
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Cited by 1 (0 self)
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Abstract. Magnetic fields correlated on kiloparsec scales are seen in spiral galaxies. Their origin could be due to amplification of a small seed field by a turbulent galactic dynamo. We review the current status of the galactic dynamo, especially the constraints imposed by magnetic helicity
Fluid helicity and dynamo effect
"... Using the incompressible magnetohydrodynamic equations, we have numerically studied the dynamo effect in electrically conducting fluids. The necessary energy input into the system was modeled either by an explicit forcing term in the NavierStokes equation or fully selfconsistently by thermal convec ..."
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of the forcing is further raised were studied, including the transition to chaotic states. Special attention was paid to the helicity of the flow as well as to the symmetries of the system and symmetry breaking in the bifurcations. The magnetic field tends to be accumulated in special regions of the flow
Fluid Helicity and Dynamo Bifurcations
 Phys. Lett. A
"... The bifurcation behaviour of the 3D magnetohydrodynamic equations has been studied for external forcings of varying degree of helicity. With increasing strength of the forcing a primary nonmagnetic steady state loses stability to a magnetic periodic state if the helicity exceeds a threshold value a ..."
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Cited by 1 (1 self)
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The bifurcation behaviour of the 3D magnetohydrodynamic equations has been studied for external forcings of varying degree of helicity. With increasing strength of the forcing a primary nonmagnetic steady state loses stability to a magnetic periodic state if the helicity exceeds a threshold value
Importance of Magnetic Helicity in Dynamos
"... Magnetic helicity is nearly conserved and its evolution equation provides a dynamical feedback on the alpha effect that is distinct from the conventional algebraic alpha quenching. The seriousness of this dynamical alpha quenching is particularly evident in the case of closed or periodic boxes. The ..."
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Magnetic helicity is nearly conserved and its evolution equation provides a dynamical feedback on the alpha effect that is distinct from the conventional algebraic alpha quenching. The seriousness of this dynamical alpha quenching is particularly evident in the case of closed or periodic boxes
1 Galactic and Accretion Disk Dynamos
, 1998
"... Dynamos in astrophysical disks are usually explained in terms of the standard alphaomega mean field dynamo model where the local helicity generates a radial field component from an azimuthal field. The subsequent shearing of the radial field gives rise to exponentially growing dynamo modes. There a ..."
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. There are several problems with this model. The exponentiation time for the galactic dynamo is hard to calculate, but is probably uncomfortably long. Moreover, numerical simulations of magnetic fields in shearing flows indicate that the presence of a dynamo does not depend on a nonzero average helicity. However
Results 1  10
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377