Measurements of spontaneous synchrotron oscillation in the SuperACO storage ring

Bunches that are propagating in the vacuum chamber of a storage ring show often instabilities in phase and energy. In the presence of parasite resonant elements, fields produced by the bunches themselves (wakefields) can induce these instabilities. We revealed the presence of one or several resonant elements by analyzing the spontaneous synchrotron oscillation (SSO). We used a measuring position on the ring where the instabilities of phase and energy are naturally present together. Measurements performed on the SuperACO storage ring in the presence of two bunches showed that the frequency of SSO depends on the current stored in the ring. These findings corroborate the hypothesis presented earlier [Bergher, AIP Conf. Proc. 367 (1995) 201; Proc. IEEE 5 (1995) 2928] that under certain conditions each bunch is transformed into a group of micro-bunches.