Nonlinear mean field electrodynamics of turbulent dynamos

Mean field electrodynamics of turbulent dynamos taking into account Lorentz forces of the generated magnetic fields is derived and studied. Small-scale magnetic fields that are much stronger than the mean field B0 modify the fluid turbulence in such a way as to suppress the α effect: α=α0(1+R)−1, where α0 is the kinematic value, and the reduction factor is proportional to the magnetic Reynolds number Rm, R=RmB20/(4πρv2), and v is the characteristic turbulent velocity. In two dimensions the analog is turbulent magnetic diffusivity suppression. Suppression becomes noticeable at very low values of the mean magnetic field, B20∼ρv2/Rm. The modification of turbulence by the small-scale magnetic fields is discussed.