1 . 1 Electron - Cloud Effects in the LHC

The LHC is the first proton accelerator for which synchrotron radiation becomes noticeable. At a beam energy of 7 TeV, the relativistic γ factor is comparable to that of electron or positron beams in the B factories or at many light sources. This means that the same number of synchrotron-radiation photons are emitted per proton and turn. The critical photon energy of about 44 eV in the LHC is near the energy of maximum photoemission yield for many materials. Therefore, a significant electron cloud can be expected from synchrotron radiation and photo-emission alone. The possibility that beam-induced multipacting may also occur in the LHC was suggested in 1996 [Grobner96]. Since 1997, electron-cloud build up in the LHC arcs due to both photoemission and beam-induced multipacting were predicted and studied in simulations [Zimmermann97,Grobner97,Bruning98]. Electron cloud effects in the LHC were reviewed previously [Rumolo01,Arduini03].