Laboratory Plasma Dynamos, Astrophysical Dynamos, and Magnetic Helicity Evolution

Abstract

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 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. flow-driven helical dynamos which amplify or sustain large scale magnetic fields in an otherwise turbulent flow, and 3. flow-driven nonhelical dynamos which amplify fields on scales at or below the driving turbulence. We discuss how all three types occur in astrophysics whereas plasma confinement device dynamos are of the first type. Type 3 dynamos requires no magnetic or kinetic helicity of any kind. Focusing on type 1 and 2 dynamos, we show how different limits of a unified set of equations for magnetic helicity evolution reveal both types. We explicitly describe a steady-state example of a type 1 dynamo, and three examples of type 2 dynamos: (i) closed volume and time dependent; (ii) steady-state with open boundaries; (iii) time dependent with open boundaries.

accepted by MNRAS

References in corpus (37)

• Astrophysical magnetic fields and nonlinear dynamo theory
• The inverse cascade and nonlinear alpha-effect in simulations of isotropic helical hydromagnetic turbulence
• Simulations of small-scale turbulent dynamo
• The case for a distributed solar dynamo shaped by near-surface shear
• Magnetic Helicity Conservation and Astrophysical Dynamos
• Experimental observation and characterization of the magnetorotational instability
• On Why Disks Generate Magnetic Towers and Collimate Jets
• Constraints on the magnitude of alpha in dynamo theory
• Inverse cascade in decaying 3D magnetohydrodynamic turbulence
• A New Dynamical Mean-Field Dynamo Theory and Closure Approach
• Magnetorotational Instability in a Rotating Liquid Metal Annulus
• Dynamic nonlinearity in large scale dynamos with shear
• Galactic dynamo and helicity losses through fountain flow
• A model of nonlinear evolution and saturation of the turbulent MHD dynamo
• Is nonhelical hydromagnetic turbulence peaked at small scales?
• Doubly Helical Coronal Ejections from Dynamos and their Role in Sustaining the Solar Cycle
• 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
• Non-Fickian diffusion and tau approximation from numerical turbulence
• A Laboratory Plasma Experiment for Studying Magnetic Dynamics of Accretion Discs and Jets
• Minimal tau approximation and simulations of the alpha effect
• Magnetic Helicity Tensor for an Anisotropic Turbulence
• Nonlinear current helicity fluxes in turbulent dynamos and alpha quenching
• The Role of Magnetic Helicity Transport in Nonlinear Galactic Dynamos
• Turbulent Dynamos and Magnetic Helicity
• Coronal activity as a consequence of dynamos in astrophysical rotators
• Magnetorotational Instability in Liquid Metal Couette Flow
• Strong mean field dynamos require supercritical helicity fluxes
• A New Approach to Turbulent Transport of a Mean Scalar
• Effect of Fractional Kinetic Helicity on Turbulent Magnetic Dynamo Spectra
• Nonlinear Turbulent Magnetic Diffusion and Mean-Field Dynamo
• Suppression of small scale dynamo action by an imposed magnetic field
• The $\alpha$ Dynamo Effects in Laboratory Plasmas
• Dynamical magnetic relaxation: A nonlinear magnetically driven dynamo
• Understanding Helical Magnetic Dynamo Spectra with a Nonlinear Four-Scale Theory
• Bihelical Magnetic Relaxation and Large Scale Magnetic Field Growth
• On the Meaning and Inapplicability of the Zeldovich Relations of Magnetohydrodynamics

Cited by in corpus (9)

• Magnetohydrodynamic experiments on cosmic magnetic fields
• The Wisconsin Plasma Astrophysics Laboratory
• Hyperdiffusion as a Mechanism for Solar Coronal Heating
• Magnetic dynamo action at low magnetic Prandtl numbers
• Turbulent processes and mean-field dynamo
• The critical role of magnetic helicity in astrophysical large-scale dynamos
• A model of driven and decaying magnetic turbulence in a cylinder
• Toward Coupling Flow Driven and Magnetically Driven Dynamos
• The Vorticity of Solar Photospheric Flows on the Scale of Granulation