The Alpha effect: The connection between cyclonic events and current helicity

Journal Article · Mon Dec 01 04:00:00 EST 1986 · IEEE Trans. Plasma Sci.; (United States)

DOI:https://doi.org/10.1109/TPS.1986.4316634· OSTI ID:6931831

Keinigs, R; Gerwin, R A

In a magnetized plasma, resistive diffusion of large-scale magnetic fields can be suppressed or even overcome by a turbulently generated electromotive force. For a plasma in which the turbulence is homogeneous and isotropic this EMF is characterized by the ensemble average (deltav x deltab) = ..cap alpha..B/sub 0/, where deltav and deltab represent the turbulent fields and B/sub 0/ defines the large-scale field. Determination of the statistical properties of the turbulence that are required to generate a finite alpha effect, as it has become known, is one of the central subjects of dynamo theory. Parker has shown that helical velocity fluctuations possessing a net amount of kinetic helicity are capable of dynamo action. These ''cyclonic events'' produce electromagnetic fluctuations characterized by their own statistical properties. Within the context of ''mean-field electrodynamics'' the authors show that these fluctuations possess a net amount of current helicity, and find that a necessary condition for dynamo action is that the turbulent current helicity and the current helicity in the large-scale field be of opposite sign.

• Research Organization: Los Alamos National Lab., Los Alamos, NM 87545
• OSTI ID: 6931831
• Journal Information: IEEE Trans. Plasma Sci.; (United States), Journal Name: IEEE Trans. Plasma Sci.; (United States) Vol. PS-14:6; ISSN ITPSB
• Country of Publication: United States
• Language: English

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