Optimal Excitation of Magnetic Fields

Brian F. Farrell, Petros J. Ioannou
1999 Astrophysical Journal  
The mechanism by which large-scale magnetic Ðelds in stars and galaxies arise remains uncertain, but it is believed that initially small internally generated or primordial seed Ðelds are ampliÐed and organized by motions in the conducting Ñuid interiors of these bodies. Methods for analyzing this process in the weak Ðeld limit are based on the induction equation and fall into two classes : those involving advection of the magnetic Ðeld as a passive tracer, and those involving calculation of
more » ... nential instabilities. The former is a nonmodal stability analysis, while the latter is essentially modal. In this work these two methods of analysis are synthesized, making use of recent advances in the theory of nonnormal system dynamics. An application of this generalized stability analysis to the helical dynamo model of Lortz is described in which the maximum Ðeld growth over prescribed time intervals and the perturbation structures producing this growth are identiÐed.
doi:10.1086/307662 fatcat:b2qjrmxmozavjawthqpsz66fyy