Transverse Behaviour of the LHC Proton Beam in the SPS: an Update

During the 1999 SPS run, strong transverse instabilities were observed with the LHC beam [1]. Both the instability characteristics and the identical threshold current as for beam-induced electron multipacting led to consider the interaction of the beam with the electron cloud as a likely source. In 2000, we have measured the dependence of beam motion, beam loss, and emittance growth on bunch intensity, number of bunches, octupole strength, chromaticity, and gaps in the bunch train. We report on these recent studies and compare the beam observations with simulations of electron cloud build up and electron-induced single-bunch instabilities.