Development of a Fast Betatron Tune and Chromaticity Measurement System Using Bunch-by-Bunch Position Monitoring

The betatron tune and its dependence on the momentum (chromaticity) are essentialquantities of circular particle accelerators. The tune must be monitored in order toavoid optical resonances which cause instabilities and limit the lifetime of the storedparticle beam. Control of the tune and chromaticity are also required to achieve longcoherence times in spin polarization experiments as carried out by the JEDI collaboration.In the scope of the present thesis, a fast betatron tune and chromaticity measurementsystem is developed for the Cooler Synchrotron COSY. The betatron oscillations ofthe beam are excited through stripline electrodes with a white noise RF signal in anappropriate frequency band. Resonant transverse oscillations are then observed usingcapacitive beam position monitors. Characteristic for the newly developed system isthe determination of the betatron tune from bunch-by-bunch beam position measurements.This allows for time-discrete tune measurements within a few milliseconds aswell as continuous tune monitoring – for example during the acceleration ramp.The high precision tune measurement also enables determination of the beam chromaticity.Therefore, the beam momentum is varied by means of RF frequency sweepsand the subsequent tune change is measured. For routine use during beam operationand experiments, the developed method is integrated into the control system.Finally, measurements showing the operational capabilities and limits of the methodare presented. The influence of different parameters on the signal strength is analysed.For commissioning, control of the betatron tune and compensation of the chromaticityare demonstrated