$\alpha$-effect dynamos with zero kinetic helicity
Karl-Heinz R\"{a}dler and Axel Brandenburg

A simple explicit example of a Roberts--type dynamo is given in which the $\alpha$--effect of mean--field electrodynamics exists in spite of point--wise vanishing kinetic helicity of the fluid flow. In this way it is shown that $\alpha$--effect dynamos do not necessarily require non--zero kinetic helicity. A mean--field theory of Roberts--type dynamos is established within the framework of the second--order correlation approximation. In addition numerical solutions of the original dynamo equations are given, that are independent of any approximation of that kind. Both theory and numerical results demonstrate the possibility of dynamo action in the absence of kinetic helicity. Key words: Mean--field dynamo action, $\alpha$--effect, modified Roberts dynamo

© 2008 The American Physical Society.