The SPS as a Vacuum Test Bench for the Electron Cloud Studies with LHC Type Beams

The SPS machine has been operating with LHC-type beams with bunch intensities up to 8x1010 protons (70% of LHC nominal intensity). This paper will give evidence of the electron cloud phenomenon as the mechanism responsible for the pressure rises in the SPS in presence of LHC type beams. The dependence of the pressure rise and of the electron current measured with dedicated pick-ups on various beam characteristics such as proton bunch intensity, number of bunches needed to start the e-cloud phenomenon and the effect of missing bunches will be presented. The evolution of the pressure rise with the integrated current ('beam scrubbing') will be discussed. The observed effect of the dipole magnetic field and of the treatment of the stainless steel vacuum chambers with N2 glow discharge on the pressure rise and on its evolution with the integrated current will be also considered. Finally, the consequences of the electron cloud build-up on the SPS vacuum system for the LHC beam nominal intensity will be described.