  The shell-to-shell energy transfer rates for magnetohydrodynamic (MHD)
turbulence are computed analytically, which shows local energy transfer rates
from velocity to velocity, velocity to magnetic, magnetic to velocity, and
magnetic to magnetic fields for nonhelical MHD in the inertial range. It is
also found that for kinetic-energy dominated MHD fluid, there is a preferential
shell-to-shell energy transfer from kinetic to magnetic energy; the transfer is
reversed for magnetic-energy dominated MHD fluid. This property is the reason
for the asymptotic value of Alfven ratio to be close to 0.5. The analytical
results are in close agreement with recent numerical results. When magnetic and
kinetic helicities are turned on, the helical contributions are opposite to the
corresponding nonhelical contributions. The helical energy transfers have
significant nonlocal components.
