Electron Cloud Studies and Beam Scrubbing Effect in the SPS

The performance of the SPS as LHC injector has been limited, with LHC-type beams, by the electron cloud multipacting for high bunch intensities (>6.0x10**10 protons/bunch). To study in detail the dependence of the electron cloud on the beam parameters (bunch intensity, filling pattern, filling factor...), three strip-detectors have been installed inside dipole corrector magnets. The measuring set-up was completed by shielded pick-ups and by an in-situ secondary electron yield detector installed in field-free regions. This paper presents the variation of the electron cloud activity as a function of the bunch intensity and bunch length, filling pattern and filling factor. The spatial and energy distributions of the electrons in the cloud were studied and the latter compared with results obtained with a conventional retarding field detector. Evidence of the scrubbing effect as a solution to reduce the electron cloud activity is shown in the SPS. Heat load estimations based on the electron cloud intensity and on their energy distributions are given as a function of the bunch intensity and filling factor. The results can be compared with independent direct calorimetric measurements. The implications for the LHC are discussed, in particular heat load extrapolations and a possible start up scenario.