Pressure and Heat Load in a LHC Type Cryogenic Vacuum System Subjected to Electron Cloud

The electron cloud is of major concern for most of the storage rings operating with large bunch currents and low bunch spacing. The Large Hadron Collider (LHC) operated at cryogenic temperature will have to face the electron cloud when running with proton beams. For this reason, the first experimental studies related to the electron cloud in a LHC type cryogenic vacuum system have been launched in 2002 after the closure of the Electron Positron Accumulator (EPA) synchrotron radiation experimental program. The cold bore experiment (COLDEX) has been installed in the CERN Super Proton Synchrotron (SPS) where electron clouds could be produced with proton beams. The detailed results of the investigations, which include measurements of the dynamic heat deposition, dynamic total pressure rise and residual gas composition as a function of beam operation dose will be presented. The beam conditioning efficiency is studied as a function of temperature. The results of dedicated experiments with pre-condensed gas layers onto the beam screen are shown. The preliminary results with 75 ns bunch spacing are presented. The experimental results obtained as a function of beam operation dose are compared to the outputs of the ECLOUD simulation code. Finally, the implications to the LHC design and operation are discussed.