Damping of Coherent Transverse Oscillations in PETRA

A narrow band bunch-by-bunch feedback system has been installed in PETRA in order to damp all modes of coherent transverse bunch oscillations. The system consists of pick up electrodes, a damping kicker and 8 parallel channels that each detect the oscillation signal of one particular bunch. The loop phase error due to machine tune shift is automatically corrected by a compensating network. At large betatron amplitudes, the damping kicker reaches its power limit. Taking this nonlinearity into account, the damping of the system was calculated and was found to bein good agreement with the measured values. During the first experimental runs with 4 bunches the feedback system was successfully used.