Measurement and Compensation of Betatron Resonances at the CERN PS Booster Synchrotron

The CERN PS Booster synchrotron is the first circular accelerator in the proton injector chain of the future Large Hadron Collider and links the linear accelerator, Linac2, with the Proton Synchrotron. Apart from serving as a pre-injector for the LHC, the PS Booster provides high intensity beams for the ISOLDE physics facility and various other beams for the Proton Synchrotron and its users. The 50 MeV proton beam coming from Linac2 is accumulated in the PS Booster by means of a multi-turn-injection scheme. Throughout injection, rf-capture and early acceleration, the individual particles in the beam “see” large, fluctuating incoherent space-charge tune shifts, consequently sweeping a large area in the tune diagram and covering many resonances. Thus, the beam suffers amplitude blow-up from transverse betatron resonances and an efficient compensation is required to avoid subsequent particle losses. The presently used resonance compensation scheme was established 25 years ago by orthogonal search of coupled magnet currents minimising beam losses. With the increasing demands for higher intensities and higher brightness beams, a revision of the existing working point with a general analysis of all relevant betatron resonances was proposed for the thesis. The combination of fast electronics, powerful computing tools and Normal Form techniques now make it possible to evaluate amplitude and phase of resonance driving terms from turn-by-turn beam position measurements. The specific goals of the thesis were: • Defining an acquisition system for beam position measurement over many turns with storage and analysis. • Implementation of the system as a tool for standard operation on the PS Booster. • Measurement of resonance excitation and comparison to simulations. • Verification and potential improvement of the existing compensation scheme. • Search for an alternative new working point with lower intrinsic excitation and efficient compensation. The measurement programme implemented in the thesis favoured the choice of a new working point for the PS Booster and culminated in a complete evaluation of the amplitude and phase of driving terms for all the resonances relevant to operation.