Magnetic Helicity Density and Its Flux in Weakly Inhomogeneous Turbulence

A gauge invariant and hence physically meaningful definition of magnetichelicity density for random fields is proposed, using the Gauss linkingformula, as the density of correlated field line linkages. This definition isapplied to the random small scale field in weakly inhomogeneous turbulence,whose correlation length is small compared with the scale on which theturbulence varies. For inhomogeneous systems, with or without boundaries, ourtechnique then allows one to study the local magnetic helicity densityevolution in a gauge independent fashion, which was not possible earlier. Thisevolution equation is governed by local sources (owing to the mean field) andby the divergence of a magnetic helicity flux density. The role of magnetichelicity fluxes in alleviating catastrophic quenching of mean field dynamos isdiscussed.Comment: 4 pages, accepted by Ap