### Abstract

Diffusion of a magnetic field through a plasma is discussed in one-, two- and three-dimensional configurations, together with the possibility of describing such diffusion in terms of a magnetic flux velocity, which, when it exists, is in general non-unique. Physically useful definitions of such a velocity include doing so in terms of the energy flow or in such a way that it vanishes in a steady state. Straight field lines (or plane flux surfaces) diffuse as if flux is disappearing at a neutral sheet, whereas circular field lines (or cylindrical flux surfaces) do so as if flux is disappearing at an 0-type neutral line. In three dimensions it is not always possible to define a flux velocity, for example when the magnetic flux through a closed field line is changing in time. However, in at least some such cases it is possible to describe the behaviour of the magnetic field in terms of a pair of quasi-flux-velocities.

Original language | English |
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Pages (from-to) | 177-197 |

Number of pages | 21 |

Journal | Geophysical & Astrophysical Fluid Dynamics |

Volume | 99 |

Issue number | 2 |

DOIs | |

Publication status | Published - 2005 |

### Keywords

- Magnetohydrodynamics (MHD)
- Magnetic diffusion
- Plasmas
- MHD

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## Cite this

Wilmot-Smith, A. L., Priest, E. R., & Hornig, G. (2005). Magnetic diffusion and the motion of field lines.

*Geophysical & Astrophysical Fluid Dynamics*,*99*(2), 177-197. https://doi.org/10.1080/03091920500044808