Effects of a 500 Mc s−1 additional cavity on spontaneous coherent synchrotron oscillations in the Super-ACO storage ring

An additional 500 Mc s−1 cavity, fifth harmonics of the main cavity, was installed on the Super-ACO storage ring in order to shorten the bunch length. This cavity was introduced to obtain shorter wavelengths in the UV for the FEL and shorter flashes of light for the experiments using the two-bunches-mode functioning for the time-resolved measurements. Spontaneous coherent synchrotron oscillations (SCSO) were profoundly modified by the presence of this cavity. These instabilities are probably the consequence of the formation of micro-bunches. The vanishing of these micro-bunches is associated to the emission of coherent synchrotron radiation, which gives the SCSO a cyclic character. The identification of the resonant elements responsible for these cyclic instabilities can help us to suppress or substantial ameliorate the SCSO by acting selectively on these resonant elements. This method can be applied to other storage or damping rings that show the same type of instabilities.