Interplay of Ionization and Sputtering with the Electron Cloud

The electron cloud enhances the generation and accumulation of ions, which in turn might increase both electron density and electron decay time. We report analytical considerations and simulations of ion motion under the combined influence of beam, electron cloud, and various external magnetic fields. From these, we infer ion survival times, ion impact energies and the equilibrium ion density. All of these are shown to be small. Only in a dipole field whose ion cyclotron frequency is resonant with the bunch spacing (2.62 T for hydrogen ions in the LHC) some ions may acquire kinetic energies of several keV. We argue that additional contributions from ion reflection and sputtering are insignificant.