EFFECTIVE AMPERE FORCE IN DEVELOPED MAGNETOHYDRODYNAMIC TURBULENCE

The interaction between a large-scale uniform weak magnetic field B an d a developed small-scale magnetohydrodynamic (MHD) turbulence is stud ied. It is found that the effective mean Ampere force in the turbulenc e is given by F-m=-V(Q(p)B(2)/8 pi)+(B.V)Q(3)B/4 pi. The turbulent mag netic coefficients Q(p) and Q(s) are drastically decreased at large ma gnetic Reynolds numbers, whereas in the absence of turbulence Q(p)=Q(s )=1. This phenomenon arises due to a negative contribution of the MHD turbulence to the mean magnetic force. This is caused by the generatio n of magnetic fluctuations at the expense of fluctuations of the veloc ity field. This effect is nonlinear in terms of the large-scale magnet ic field. It is shown here that in turbulence with a mean large-scale magnetic field, a universal k(-1) spectrum of magnetic fluctuations ex ists; this spectrum is independent of the exponent of the spectrum of the turbulent velocity field. A variant of the renormalization group ( RNG) method allows the derivation of the scaling and amplitude of the turbulent transport coefficients: turbulent viscosity, turbulent magne tic diffusion, and turbulent magnetic coefficients. A small parameter in the RNG method is the ratio epsilon=B-2/(8 pi W-k) of the large-sca le magnetic energy density to the energy density W-k=(1/2)rho[u(2)] of the turbulent velocity field.