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 B-0 modify the fluid turbulence in such a way as to suppress the alpha effect: alpha=alpha(0)(1+R)(-1), where alpha(0) is the kinematic value, and the reduction factor is proportional to the magnetic Reynolds number R(m), R=R(m)B(0)(2)/(4 pi rho upsilon(2)), and upsilon 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, B-0(2) similar to rho upsilon(2)/R(m). The modification of turbulence by the small-scale magnetic fields is discussed. (C) 1996 American Institute of Physics.