Limitations due to Electron-Cloud Heat Load for the LHC and its Upgrade

In the LHC beam pipe, an electron cloud can build up due to photoemission from synchrotron radiation and via a beam-induced multipacting process. This electron cloud gives rise to an additional heat load on the beam screen which protects the cold bore of the superconducting magnets. The heat load from the electron cloud depends on beam parameters such as the bunch intensity, the number of bunches, the bunch length, and the bunch spacing, as well as on surface parameters, in particular the maximum secondary emission yield and the elastic reflectivity of lowenergy electrons. The maximum tolerable heat load is determined by the available cooling capacity. Simulations of the electron-cloud induced heat load in various LHC configurations yield the limiting values of secondary emission yield and reflectivity which are required at 25-ns bunch spacing to reach the nominal and ultimate LHC parameters, respectively, at 12.5-ns bunch spacing for a ‘conventional upgrade’, and at 75-ns bunch spacing for an upgrade in the regime of a large Piwinski parameter.