Can we look inside a dynamo?

Abstract

For a simple spherically symmetric mean-field dynamo model we investigate the possibility of determining the radial dependence of the coefficient $α$. Growth rates for different magnetic field modes are assumed to be known by measurement. An evolutionary strategy (ES) is used for the solution of the inverse problem. Numerically, we find quite different $α$-profiles giving nearly the same eigenvalues. The ES is also applied to find functions $α(r)$ yielding zero growth rates for the lowest four magnetic field modes. Additionally, a slight modification of the ES is utilized for an ''energetic'' optimization of $α^2$-dynamos. The consequences of our findings for inverse dynamo theory and for the design of future dynamo experiments are discussed.