Electron cloud with LHC-type beams in the SPS: A review of three years of measurements

In August 1999, high bunch intensities LHC-type beams were injected for the first time in the SPS inducing strong vacuum pressure rises, perturbations on the electrostatic pick-ups and beam instabilities. Evidences of the electron cloud phenomenon as the mechanism responsible for these instabilities are reviewed. This paper also presents the results obtained with several detectors installed in the SPS machine to improve the understanding of the electron cloud mechanism and refine the simulations. The spatial distributions of the electrons in the cloud are shown in presence of and without a dipole magnetic field. The effects of the beam intensity and filling pattern on the behaviour of the electron cloud are presented. The scrubbing effect is studied using an in-situ measurement of the secondary electron yields. Finally, the potential limitations due to the electron cloud in the SPS and the issues for the LHC are discussed. Possible remedies will be presented, i.e. nitrogen and argon glow discharges or new filling schemes.