Laboratory plasma dynamos, astrophysical dynamos and magnetic helicity evolution

Eric G. Blackman, Hantao Ji

Research output: Contribution to journalArticle

11 Scopus citations

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 towards 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 non-helical 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 require no magnetic or kinetic helicity of any kind. Focusing on Types 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.

Original languageEnglish (US)
Pages (from-to)1837-1848
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Volume369
Issue number4
DOIs
StatePublished - Jul 2006

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Accretion, accretion discs
  • MHD
  • Magnetic fields
  • Methods: laboratory
  • Stars: coronae
  • Sun: coronal mass ejections (CMEs)

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