Longitudinal beam dynamics and FEL interaction on a negative momentum compaction storage ring

A simulation study for longitudinal phase space of the electron bunch including effects of potential-well distortion and FEL interaction has been performed for both positive and negative momentum compaction factors on a storage ring. The trend of the bunch lengthening is well interpreted by the wake field due to inductive impedance. In spite of large energy spread in the case of the negative momentum compaction, FEL oscillation may be possible. The peak power of Q-switched lasing is higher than that in positive momentum compaction. There was, however, no significant difference in FEL power and particle distribution in the longitudinal phase space at the equilibrated state.