The generation of magnetic fields through driven turbulence

We have tested the ability of driven turbulence to generate magnetic field structure from a weak uniform held using three-dimensional numerical simula tions of incompressible turbulence. We used a pseudospectral code with a nu merical resolution of up to 144(3) collocation points. We find that the mag netic fields are amplified through held line stretching at a rate proportio nal to the difference between the velocity and the magnetic field strength times a constant. Equipartition between the kinetic and magnetic energy den sities occurs at a scale somewhat smaller than the kinetic energy peak. Abo ve the equipartition scale the velocity structure is, as expected, nearly i sotropic. The magnetic held structure at these scales is uncertain, but the field correlation function is very weak. At the equipartition scale the ma gnetic fields show only a moderate degree of anisotropy, so the typical rad ius of curvature of held lines is comparable to the typical perpendicular s cale for field reversal. In other words, there are few held reversals withi n eddies at the equipartition scale and no fine-grained series of reversals at smaller scales. At scales below the equipartition scale, both velocity and magnetic structures are anisotropic; the eddies are stretched along the local magnetic field lines, and the magnetic energy dominates the kinetic energy on the same scale by a factor that increases at higher wavenumbers. We do not show a scale-free inertial range, but the power spectra are a fun ction of resolution and/or the imposed viscosity and resistivity. Our resul ts are consistent with the emergence of a scale-free inertial range at high er Reynolds numbers.