Dynamo theories
Abstract
These lecture notes are based on a tutorial given in 2017 at a plasma physics winter school in Les Houches. Their aim is to provide a selfcontained graduatestudent level introduction to the theory and modelling of the dynamo effect in turbulent fluids and plasmas, blended with a review of current research in the field. The primary focus is on the physical and mathematical concepts underlying different (turbulent) branches of dynamo theory, with some astrophysical, geophysical and experimental contexts disseminated throughout the document. The text begins with an introduction to the rationale, observational and historical roots of the subject, and to the basic concepts of magnetohydrodynamics relevant to dynamo theory. The next two sections discuss the fundamental phenomenological and mathematical aspects of (linear and nonlinear) small and largescale magnetohydrodynamic (MHD) dynamos. These sections are complemented by an overview of a selection of current active research topics in the field, including the numerical modelling of the geo and solar dynamos, shear dynamos driven by turbulence with zero net helicity and MHDinstabilitydriven dynamos such as the magnetorotational dynamo. The difficult problem of a unified, selfconsistent statistical treatment of small and largescale dynamos at large magnetic Reynolds numbers is also discussed throughout the text. Finally, an excursion is made into the relatively new but increasingly popular realm of magneticfield generation in weakly collisional plasmas. A short discussion of the outlook and challenges for the future of the field concludes the presentation.
 Publication:

Journal of Plasma Physics
 Pub Date:
 August 2019
 DOI:
 10.1017/S0022377819000539
 arXiv:
 arXiv:1903.07829
 Bibcode:
 2019JPlPh..85d2001R
 Keywords:

 astrophysical plasmas;
 plasma dynamics;
 plasma nonlinear phenomena;
 Physics  Plasma Physics;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Solar and Stellar Astrophysics;
 Physics  Fluid Dynamics;
 Physics  Geophysics
 EPrint:
 Published in J. Plasma Phys. lecture note series. Final author's version (pre copyediting), 163 pages, 48 figures. The quality of some figures in this version has been deliberately downgraded to fit into the arXiv