Stable motion of highly energetic particles interacting via a repelling potential

Consider a system of any given number of particles confined in a box and interacting via a smooth repelling potential. We show that for a generic choice of the potential, if the energy is sufficiently high, then there exists a totally elliptic periodic orbit surrounded by a positive measure set of KAM-tori. This implies that such systems are not ergodic for all sufficiently high energies.