Magnetic-field generation and turbulence suppression due to cross-helicity effects

Abstract

The regeneration mechanism of magnetic fields in turbulent motion is studied using a turbulent dynamo model, in which effects of global plasma rotation are incorporated through the turbulent cross helicity (velocity/magnetic-field correlation). The turbulent model consists of the mean-field equations and the transport equations for turbulent quantities such as the turbulent energy, its dissipation rate, and the turbulent cross helicity. Prominent properties of the cross-helicity effect, such as the direct linkage to the mean vortical motion, the alignment of the mean electric current and the mean vorticity, etc., are discussed in comparison with the helicity or α effect. This model is applied to simple plasma flows, such as a cylindrical pipe and an accretion disk. The numerical results show that the turbulence suppression and magnetic-field generation due to the cross-helicity effects occur in the presence of mean vortical motion. The possible cross-helicity production mechanisms are also discussed.