Notes on the cross-helicity effects

Abstract

    Turbulent cross helicity (correlation between the velocity and magnetic-field .uctuations) is expected to play an important role in several magnetohydrodynamic (MHD) plasma phenomena such as global magnetic-field generation, turbulence suppression, etc. First we present physical interpretation of the cross-helicity effect; A combination of the local angular-momentum conservation and the cross-correlation between the velocity and magnetic-field fluctuation gives rise to the contribution to the turbulent electromotive force parallel to the large-scale vorticity. A microscopic origin of the effect is also presented with the aid of the notion of polarization drift. The conservative nature of the cross helicity is examined with special reference to the cross-helicity supplying mechanism to turbulence and mean flows. This point is important in considering the boundary condition for the numerical test of the cross-helicity effect. [This abstract is not included in the PDF]