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Description
The build-up of an electron cloud and beam-induced electron multipacting was first observed in a test chamber in the ISR at CERN in 1977. In the positron rings of KEKb and PEP-II beauty factories, pronounced pressure rises were observed earlier this year during machine commissioning as the beam current exceeded a threshold. These
dynamic pressure rises are due to electron multipacting and/or ion-induced desorption.
Most recently in the SPS at CERN electron multipacting has been unambiguously observed in the presence of LHC type beams. The initial LHC design studies identified electron multipacting as a potentially serious problem for the vacuum system and it was recognised that detailed investigations of the phenomenon would be required. Since 1996 extensive studies have been undertaken to quantify and assess the detrimental effects of such an electron cloud on the cryogenic vacuum system of the LHC. In this talk an overview of the electron cloud key parameters, related to the material properties of the vacuum chamber wall, will be identified together with examples of how such parameters
are quantified. The implications on the LHC beam screen design of the predicted heat loads will be given. Laboratory based investigations, identifying possible remedies to avoid excessive heat loads and pressure rises due to electron bombardment, will be discussed.
