Effect of alpha quenching on magnetic field size - art. no. 056404

It is commonly assumed that the a effect of mean-field magnetohydrodynamics essentially stops acting wherever the mean-field size reaches a certain va lue. We show that if the mean velocity is approximately constant, the regio ns where the field reaches such a threshold tend to shrink in size or the f ield tends to become constant there. The rate of this process is also estim ated.