COHERENT SYNCHROTRON OSCILLATION INDUCED BY A PLL NOISE IN THE KEK PHOTON FACTORY STORAGE RING

摘要

In the 2.5-GeV Photon Factory (PF) storage ring at KEK, a coherent synchrotron oscillation of the stored bunches has been observed. This oscillation appears in a beam spectrum as the synchrotron sidebands beside rf harmonics, or it can be observed directly using a streak camera. It emerges even under a very low beam current of 1 mA or less, and its amplitude becomes small at high currents. Therefore, this oscillation could not be attributed to any beam instabilities. We have recently identified that this oscillation was mainly caused by a phase noise in an rf voltage. The noise was produced by a phase-lock loop (PLL) circuit in a low-level rf system. We report both an experimental investigation and a cure for this oscillation.