  In gyrokinetic theory, the quadratic nonlinearity is known to play an
important role in the dynamics by redistributing (in a conservative fashion)
the free energy between the various active scales. In the present study, the
free energy transfer is analyzed for the case of ion temperature gradient
driven turbulence. It is shown that it shares many properties with the energy
transfer in fluid turbulence. In particular, one finds a forward (from large to
small scales), extremely local, and self-similar cascade of free energy in the
plane perpendicular to the background magnetic field. These findings shed light
on some fundamental properties of plasma turbulence, and encourage the
development of large eddy simulation techniques for gyrokinetics.
