On the role of Alfvén resonance in the electromotive force
by
Albano 3: 6335 - Hekto (10 seats)
Albano Building 3
The mechanisms by which wave energy may be absorbed in Alfvén resonant layers and cause heating of laboratory plasmas and coronal flux tubes are well known. Similar transfer of energy between waves and mean flux components also frequently takes place in large-scale dynamos. However, in the latter case the precise nature of this absorption mechanism has largely been overlooked in the interest of analysing the electromotive force (EMF) responsible for the magnetic induction in terms of mean-field quantities. In this study, a first-order solution valid in the vicinity of an Alfvén resonant layer is derived for a cylindrical plasma described by the coupled incompressible Navier–Stokes and induction equations. The solution is used to obtain an analytical expression for the EMF due to waves that arise from a magnetohydrodynamic (MHD) instability. This exposes the functional dependency of the EMF on the background state and the wave properties, and enables specific criteria for the existence of a non-zero wave EMF to be formulated. In addition, an expression for the group velocity and a detailed account of the energy absorption in the resonant layers are provided. The formulation is general and applicable to EMFs arising from waves due to either the magnetorotational instability (MRI) or the ‘kink’/Tayler instability. The concepts are illustrated in a one-dimensional model of a Keplerian disc.
https://www.tandfonline.com/doi/full/10.1080/03091929.2025.2565545