  Kinetic theory of nonlinear current response to an external field is
developed for mesoscopic normal metal rings threaded by a magnetic flux.
General expressions for direct current (DC) are derived for a non-equilibrium
regime. These expressions describe simultaneously a contribution to DC made by
a non-equilibrium (external) field, as well as the contribution caused by
interaction with intrinsic fields. Contributions of electron-electron and
electron-phonon interactions to the direct current in a non-equilibrium systems
are studied. The kinetic equation for electrons in a disordered metal ring is
solved with taking into account the Coulomb and electron-phonon interactions.
This gives an estimate of an overheating of the pumped electron system.
