Saturation of large-scale dynamo in anisotropically forced turbulence
  Turbulent dynamo theories have faced difficulties in obtaining evolution of
large-scale magnetic fields on short dynamical time-scales due to the
constraint imposed by magnetic helicity balance. This has critical implications
for understanding the large-scale magnetic field evolution in astrophysical
systems like the Sun, stars and galaxies. Direct numerical simulations (DNS) in
the past with isotropically forced helical turbulence have shown that
large-scale dynamo saturation time-scales are dependent on the magnetic
Reynolds number (Rm). In this work, we have carried out periodic box DNS of
helically forced turbulence leading to a large-scale dynamo with two kinds of
forcing function, an isotropic one based on that used in PENCIL-CODE and an
anisotropic one based on Galloway-Proctor flows. We show that when the
turbulence is forced anisotropically, the nonlinear (saturation) behaviour of
the large-scale dynamo is only weakly dependent on Rm. In fact the magnetic
helicity evolution on small and large scales in the anisotropic case is
distinctly different from that in the isotropic case. This result possibly
holds promise for the alleviation of important issues like catastrophic
quenching.
