The mean energy of a decaying magnetic field in MHD-turbulence

A magnetic field which is contained in a turbulent, electrically conducting fluid is supposed to decay. The decay time of the mean energy of the fluctuating part of the magnetic field – in contrast with the energy of the mean field – is shown to be determined by the molecular magnetic diffusivity and the correlation length of the turbulence. The investigation is carried out for weak magnetic fields in homogeneous isotropic mirror-symmetric turbulence and in the framework of the second-order correlations approximation.