Vacuum pressure observations during 2011 proton run

During the 2011 LHC proton run, different dynamic vacuum effects were detected and analysed in the LHC: electron cloud, synchrotron radiation, pressure spikes and beam induced heating effects . Electron clouds (EC) build up and pressure rises were measured with different bunch spacings and in different positions of the LHC. After a scrubbing run period performed in April 2011, the secondary electron yield of the vacuum surfaces was reduced to a level so that the EC effect was not anymore a limiting factor for the operation. Pressure spikes during injection, energy ramp and stable beams were observed mainly in LSS2 and LSS8 and in some cases lead to beam dumps. Beam induced heating effects were detected in different locations of the accelerator, mainly in TDI, MKI and TCP collimators in LSS7. This paper reviews all these observations and summarizes the mitigation solutions deployed for each location during the Winter Technical Stop (WTS) 2011-2012.