Beam Vacuum Chamber Effects It the CERN Large Hadron Collider

The vacuum chamber of the Large Hadron Collider (LHC) which could be installed above LEP in the LEP tunnel, would be maintained at liquid helium temperature. The power losses from the beam induced wall currents should be minimized in order to reduce the heat load on the cryogenic system. it is shown that stainless steel leads to unacceptably high heating rates due to its high resistivity. On the contrary, the study of the beam chamber coupling impedance shows that with a copper plated vacuum chamber the losses for the LHC beam could be kept below 14 mWm-1, which is much smaller than the unavoidable synchrotron radiation losses. The data on resistivity and impedance are further exploited to evaluate beam stability. The conclusions are that the nominal beam is stable for the resistive wall effect and has comfortable safety margins for the transverse mode coupling, the longitudinal microwave and coupled bunch instabilities.