The LHC proton beam in the CERN SPS: an update

During the 2001 run the beam-induced electron-cloud, generating dramatic vacuum pressure increases and fast transverse instabilities, was the main limitation in the achievement of the nominal LHC beam intensity in the SPS. Nominal longitudinal and transverse parameters at the extraction energy (450 GeV) could be achieved only with a single batch and with a maximum bunch population of 0.5×10¹¹ p. In 2002 the threshold for the onset of the electron cloud in the arcs could be increased from 0.4×10¹¹ p/bunch to 0.9×10¹¹ p/bunch by means of a dedicated 10-day ´scrubbing´ run with the LHC beam. At the end of this period four LHC batches with design bunch population (1.1×10¹¹ p) could be injected for each SPS cycle, as foreseen for the nominal filling scenario, without provoking vacuum interlocks. After a series of machine development sessions the LHC beam with nominal intensity could be accelerated to 450 GeV with nominal longitudinal emittance and with transverse emittances close to the design values for the first three batches. The problems encountered with this high brilliance beam and the solutions developed are presented.