  The acceleration of ions in the interaction of circular polarized laser
pulses with overdense plasmas is investigated. For circular polarization laser
pulses, the quasi-equilibrium for electrons is established due to the light
pressure and the electrostatic field built up at the interacting front of the
laser pulse. The ions located within the skin-depth of the laser pulse can be
synchronously accelerated and bunched in the charge couple processes by the
electrostatic field, and thereby monoenergetic and high intensity proton beam
can be generated. The dynamics equations for accelerated ions are deduced and
proved by particle-in-cell simulations.
