Design and tuning of digital filters for RF feedback loops in heavy-ion synchrotrons

Damping of longitudinal coherent bunched-beam oscillations are needed in SIS18 and SIS100 to stabilize the beam, prevent emittance growth and keep beamloss low during acceleration. In last year’s work several approaches of digital filters for beam-phase control have been examined. An FIR (finite impulse response) filter with 3 taps, cf. [1], has been successfully used at GSI in several machine experiments for a beam- phase control system and a longitudinal feedback system. In principle, much more taps can be used, but it is still an open topic, whether more complex filters will lead to better results. Therefore, a detailed control-theoretic study has been started and the progress is reported in the following