It is typically assumed that the kinetic and magnetic helicities play a
crucial role in the growth of large-scale dynamo. In this paper we demonstrate
that helicity is not essential for the amplification of large-scale magnetic
field. For this purpose, we perform nonhelical magnetohydrodynamic (MHD)
simulation, and show that the large-scale magnetic field can grow in nonhelical
MHD when random external forcing is employed at scale 1/10 the box size. The
energy fluxes and shell-to-shell transfer rates computed using the numerical
data show that the large-scale magnetic energy grows due to the energy
transfers from the velocity field at the forcing scales.Comment: 8 pages, 13 figure
