Review of beam instabilities in the presence of electron clouds in the LHC

Recent observations at the LHC indicate the build-up of electron clouds when 50 ns spaced beams are injected into the machine at nominal intensity. These electron clouds are a source of coherent beam instabilities and incoherent emittance growth and limit the achievable luminosity. To better understand the influence of electron clouds on the beam dynamics, simulations have been carried out to study both the coherent and the incoherent effects on the beam. The simulations are performed with the HEADTAIL code [2]; the usage of new post-processing software allows determining not only the beam intensity thresholds in terms of the central electron cloud density but also the footprint of the beam in tune space. In this paper we review instability thresholds and tune footprints for beams with different emittances and interacting with an electron cloud in fieldfree or dipole regions.