Helicity, reconnection, and dynamo effects

Research output: Chapter in Book/Report/Conference proceedingChapter

6 Scopus citations

Abstract

The inter-relationships between magnetic helicity, magnetic reconnection, and dynamo effects are discussed. In laboratory experiments, where two plasmas are driven to merge, the helicity content of each plasma strongly affects the reconnection rate as well as the shape of the diffusion region. Conversely, magnetic reconnection events also strongly affect the global helicity, resulting in efficient helicity cancellation (but not dissipation) during counter-helicity reconnection and a finite helicity increase or decrease (but less efficiently than dissipation of magnetic energy) during co-helicity re-connection. Close relationships also exist between magnetic helicity and dynamo effects. The turbulent electromotive force along the mean magnetic field (α-effect), due to either electrostatic turbulence or the electron diamagnetic effect, transports mean-field helicity across space without dissipation. This has been supported by direct measurements of helicity flux in a laboratory plasma. When the dynamo effect is driven by electromagnetic turbulence, helicity in the turbulent field is converted to mean-field helicity. In all cases, however, dynamo processes conserve total helicity except for a small battery effect, consistent with the observation that the helicity is approximately conserved during magnetic relaxation.

Original languageEnglish (US)
Title of host publicationMagnetic Helicity in Space and Laboratory Plasmas, 1999
EditorsRichard C. Canfield, Alexei A. Pevtsov, Michael R. Brown
PublisherBlackwell Publishing Ltd.
Pages167-177
Number of pages11
ISBN (Electronic)9781118664476
ISBN (Print)9780875900940
DOIs
StatePublished - Jan 1 1999

Publication series

NameGeophysical Monograph Series
Volume111
ISSN (Print)0065-8448
ISSN (Electronic)2328-8779

All Science Journal Classification (ASJC) codes

  • Geophysics

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    Ji, H. (1999). Helicity, reconnection, and dynamo effects. In R. C. Canfield, A. A. Pevtsov, & M. R. Brown (Eds.), Magnetic Helicity in Space and Laboratory Plasmas, 1999 (pp. 167-177). (Geophysical Monograph Series; Vol. 111). Blackwell Publishing Ltd.. https://doi.org/10.1029/GM111p0167