Remarks on the equilibration of high conductivity dynamos

The saturation mechanisms for a kinematically fast dynamo are examined when the scale of the magnetic field is significantly larger than that of the f luid flow. A truncated nonlinear dynamo model is used, appropriate to high magnetic Reynolds number R-m and low Reynolds number R-c. For large-scale f ields not only is the chaotic stretching of the fluid flow suppressed but a lso the energy of the flow. The resulting strong large-scale magnetic field and low amplitude flow may be described using an alpha effect. Furthermore . magnetic fields tend to evolve to the largest scale available in the syst em.