Alexandre Lasheen

Beam Instabilities in Hadron Synchrotrons

Beam instabilities cover a wide range of effects in particle accelerators and they have been the subjects of intense research for several decades. As the machines performance was pushed new mechanisms were revealed and nowadays the challenge consists in studying the interplays between all these intricate phenomena, as it is very often not possible to treat the different effects separately. The aim of this paper is to review the main mechanisms, discussing in particular the recent developments of beam instability theories and simulations.

Lower-Harmonic RF System in the CERN SPS

Significant beam losses increasing with intensity are observed at capture and along the SPS flat bottom for the LHCtype proton beams. The intensity should be doubled for High-Luminosity LHC and high losses may be a major performance limitation. Bunches extracted from the PS, the SPS injector, are produced in a 40 MHz RF system applying a bunch rotation at the end of the cycle and therefore cannot be perfectly matched to the 200 MHz SPS RF bucket. The possibility of using a lower-harmonic, additional RF capture system in the SPS was already proposed after the LEP era in preparation for transfer of the nominal LHC beam but the bunch rotation was the preferred solution, since the induced voltage in the SPS 200 MHz RF system would be too large to ensure stability in a low harmonic system without mitigation measures. However, the use of the upgraded one-turn delay feedback and the 200 MHz RF system as a Landau cavity could help to improve beam stability. The feasibility of this scenario to reduce capture losses in the SPS is analysed and presented in this paper. The beam transfer to the main 200 MHz RF system is simulated using a realistic bunch distribution.