LHC Beam Vacuum During 2011 Machine Operation

During the year 2011 the LHC operated for 682 fills, meaning 247 days and 2 hours of stable beam in total. From 368 bunches per beam at 150 ns bunch spacing circulating in the ring in December 2010, the 2011 proton physic ended with 1380 bunches per beam circulating with 50 ns bunch spacing. The machine performances increased in parallel with the vacuum improvement thanks to a well performed scrubbing run in April 2011 and a continuous conditioning of the beam pipes while the machine was running. The 2011 LHC operation ended with one month of ions physic runs. During the machine operation various phenomena of beam - vacuum interaction were detected, analyzed and solved. This paper describes the pressure behaviour along the machine layout and mainly in specific components position like the TDI (Target Dump Injection) and the MKI injector kickers. The “pressure spike” phenomena near the experiment CMS and in some Dipole 1 (D1) regions are discussed. Finally, results obtained during the 25 ns machine developments are presented