Stability of magnetic fields with differential rotation

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The key motivation for the proposal is to resolve the puzzling situation that more and more papers about stellar structure and evolution appear that rely on nonaxisymmetric magnetic instabilities, but their existence is realized neither by laboratory experiments nor by well-defined numerical simulations. A systematic study of the angular momentum transport and the electromotive force for magnetic kink-type instabilities under the influence of slow and fast rotation is planned. For all hot stars (including slower Ap stars) the basic rotation probably dominates the inner toroidal magnetic field (Ω ≤ ΩA, ΩA Alfvén frequency) so that the results for fast rotation are important which is known to suppress the kink-type instabilities. A nonlinear spectral code for magnetic Prandtl numbers 0.01 ≤ Pm ≤ 1 in cylindric geometry is existing but its parallelization must strongly be improved. It should be used to understand the basic nonlinear saturation process of the nonaxisymmetric instabilities and to calculate • the eddy viscosity and the magnetic diffusivity in terms of the basic rotation rate and the magnetic amplitude,• the resulting helicity and the α-effect with and without density stratification.Our particular interest is to answer the question whether alternative dynamo models (‘Tayler-Spruit dynamo’) are possible on the basis of the considered magnetic instabilities or not.