In the CERN Proton Synchrotron space charge driven resonances are excited around the operational working point due to the periodicity of the optics functions. In this paper, the resonances are studied using analytical methods, i.e. the evaluation of the resonance driving terms connected to the space charge potential of Gaussian distributions. Furthermore, the resonances are characterized in measurements and simulations for various beams. The beams considered are different in terms of brightness, in order to study the dependence of the resonance strength on the space charge force.

Space charge is typically one of the performance limitations for the operation of high intensity and high brightness beams in circular accelerators. In the Proton Synchrotron (PS) at CERN, losses are observed for vertical tunes above Q y ¼ 6.25, especially for beams with large space charge tune shift. The work presented here shows that this behavior is associated to structure resonances excited by space charge due to the highly symmetric accelerator lattice of the PS, typical for first generation alternating gradient synchrotrons. Experimental studies demonstrate the dependency of the losses on the beam brightness and the harmonic of the resonance, and simulation studies reveal the incoherent nature of the resonance. Furthermore, the calculation of the resonance driving terms generated by the space charge potential shows that the operational working point of the PS is surrounded by multiple space charge driven incoherent resonances. Finally, measurements and simulations on both lattice driven and space charge driven resonances illustrate the different behavior of the beam loss depending on the source of the resonance excitation and on the beam brightness.

Space charge effects in high intensity and high brightness synchrotrons can lead to undesired beam emittance growth, beam halo formation and particle loss. A series of dedicated machine experiments has been performed over the past decade in order to study these effects in the particular regime of long-term beam storage as required for certain applications. This paper gives an overview of the present understanding of the underlying beam dynamics mechanisms, with particular emphasis on space charge induced losses and the experience gained at the CERN injector complex. The focus is on the space charge induced periodic resonance crossing, which has been identified as the main mechanism causing beam degradation for long storage times. Examples of space charge driven and error driven resonances are presented, including possible mitigation strategies. Furthermore, an outlook for possible future directions of studies is presented.

No abstract