Turbulent diffusion of large-scale magnetic fields in the presence of ambipolar drift

The decay of a large-scale magnetic field embedded in a weakly ionized fluid is studied in two-dimensional geometry. We consider cases where the magnetic energy density is less than the total kinetic energy density. Using both quasi-linear analysis and numerical simulations, we show that when the motions of the neutrals are turbulent, the effective diffusivity of a large-scale magnetic field depends on both the magnetic field strength and the frictional coupling constant between ions and neutrals. The effective diffusivity is comparable to the turbulent rate if the magnetic field is weak enough and if the frictional coupling is strong enough. However, for values of the parameters typical of the interstellar medium, we show that turbulent diffusion is bound to be reduced.