How Spectral Shapes of Magnetic Energy and Magnetic Helicity Influence their Respective Decay Time Scales

Abstract

It is shown that in magnetohydrodynamics, the shapes of the magnetic energy and magnetic helicity spectra can influence whether the magnetic helicity resistive dissipation time scale is longer, equal to, or shorter than that of magnetic energy. The calculations highlight that magnetic helicity need not always dissipate significantly more slowly than magnetic energy. While this may be implicitly understood in detailed studies of magnetic helicity in plasma devices, it is not sufficiently emphasized in elementary discussions comparing magnetic helicity vs. magnetic energy evolution. Measuring magnetic energy and helicity decay times may provide a posteriori insight into the initial spectra.

10 pages LaTeX, 1 figure, revised version, in press, Plasma Physics and Controlled Fusion

References in corpus (4)

• Is nonhelical hydromagnetic turbulence peaked at small scales?
• New Regime of MHD Turbulence: Cascade Below Viscous Cutoff
• Magnetic helicity in stellar dynamos: new numerical experiments
• Effect of Fractional Kinetic Helicity on Turbulent Magnetic Dynamo Spectra

Cited by in corpus (6)

• Astrophysical magnetic fields and nonlinear dynamo theory
• Magnetic Helicity and Large Scale Magnetic Fields: A Primer
• Accretion Disks and Dynamos: Toward a Unified Mean Field Theory
• Motivation and challenge to capture both large scale and local transport in next generation accretion theory
• Comparisons and Connections between Mean Field Dynamo Theory and Accretion Disc Theory
• Spatial Scales and Locality of Magnetic Helicity: Part 1