  We perform a detailed field theoretical study of nonequilibrium Josephson
oscillations between interacting Bose-Einstein condensates confined in a
finite-size double-well trap. We find that the Josephson junction can sustain
multiple undamped Josephson oscillations up to a characteristic time scale
$\tau_c$ without quasipartcles being excited in the system. This may explain
recent related experiments. At larger times the dynamics of the junction is
governed by fast Rabi oscillations between the descrete quasiparticle levels.
We predict that a selftrapped BEC state will be destroyed by these Rabi
oscillations.
