Abstract

The standard two-scale theory of the dynamo coefficient alpha in incompressible isotropic helical MHD turbulence is extended to include nonlinear effects of the large-scale magnetic field. We express alpha in terms of statistical quantities that can be calculated from numerical simulations for the case in which the large-scale magnetic field vanishes. For large magnetic Reynolds numbers, our formula agrees approximately with that of Kraichnan but disagrees with that of Cattaneo & Hughes.

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