Kinetic and magnetic alpha effects in nonlinear dynamo theory

Abstract

The backreaction of the Lorentz force on the alpha-effect is studied in the limit of small magnetic and fluid Reynolds numbers, using the first order smoothing approximation (FOSA) to solve both the induction and momentum equations. Both steady and time dependent forcings are considered. In the low Reynolds number limit, the velocity and magnetic fields can be expressed explicitly in terms of the forcing function. The nonlinear alpha-effect is then shown to be expressible in several equivalent forms in agreement with formalisms that are used in various closure schemes. On the one hand, one can express alpha completely in terms of the helical properties of the velocity field as in traditional FOSA, or, alternatively, as the sum of two terms, a so-called kinetic alpha-effect and an oppositely signed term proportional to the helical part of the small scale magnetic field. These results hold for both steady and time dependent forcing at arbitary strength of the mean field (abridged).

Accepted for publication in MNRAS

References in corpus (13)

• Astrophysical magnetic fields and nonlinear dynamo theory
• The inverse cascade and nonlinear alpha-effect in simulations of isotropic helical hydromagnetic turbulence
• Constraints on the magnitude of alpha in dynamo theory
• A New Dynamical Mean-Field Dynamo Theory and Closure Approach
• Dynamic nonlinearity in large scale dynamos with shear
• A Unified treatment of small and large- scale dynamos in helical turbulence
• Dynamical Quenching of the ${\alpha }^2$ Dynamo
• The Mean Electromotive Force for MHD Turbulence: the Case of a Weak Mean Magnetic Field and Slow Rotation
• Local and nonlocal magnetic diffusion and alpha-effect tensors in shear flow turbulence
• Non-Fickian diffusion and tau approximation from numerical turbulence
• Minimal tau approximation and simulations of the alpha effect
• Magnetic Helicity Tensor for an Anisotropic Turbulence
• Nonlinear Alpha Effect in Dynamo Theory

Cited by in corpus (27)

• Galactic dynamos supported by magnetic helicity fluxes
• Astrophysical turbulence modeling
• Magnetic fluctuations and formation of large-scale inhomogeneous magnetic structures in a turbulent convection
• Dynamo-driven plasmoid ejections above a spherical surface
• Test-field method for mean-field coefficients with MHD background
• Quenching and anisotropy of hydromagnetic turbulent transport
• Advances in theory and simulations of large-scale dynamos
• Large-scale instability in a sheared nonhelical turbulence: formation of vortical structures
• Turbulent diffusion with rotation or magnetic fields
• Pumping velocity in homogeneous helical turbulence with shear
• Mean-field dynamo in a turbulence with shear and kinetic helicity fluctuations
• Mean-field effects in the Galloway-Proctor flow
• Simulations of the anisotropic kinetic and magnetic alpha effects
• On the magnetic quenching of mean-field effects in supersonic interstellar turbulence
• A novel type of intermittency in a nonlinear dynamo in a compressible flow
• The kinetic helicity needed to drive large-scale dynamos
• The critical role of magnetic helicity in astrophysical large-scale dynamos
• Turbulent transport coefficients in galactic dynamo simulations using singular value decomposition
• Turbulent transport in hydromagnetic flows
• Comparison Between Turbulent Helical Dynamo Simulations and a Nonlinear Three-Scale Theory
• Alpha-effect dynamos with zero kinetic helicity
• Toward Coupling Flow Driven and Magnetically Driven Dynamos
• Iterative removal of sources to model the turbulent electromotive force
• Nonlinear turbulent magnetic diffusion and effective drift velocity of large-scale magnetic field in a two-dimensional magnetohydrodynamic turbulence
• New mechanism of generation of large-scale magnetic field in a sheared turbulent plasma
• Some helicities in electromagnetic and gravitational fields
• Closure tests for mean field magnetohydrodynamics using a self consistent reduced model