PERFORMANCE OF THE LHC PRE-INJECTORS

The LHC pre-injector complex, comprising Linac 2, the PS Booster (PSB) and the PS, has undergone a major upgrade in order to meet the very stringent requirements of the LHC. Whereas bunches with the nominal spacing and transverse beam brightness were already available from the PS in 1999 [1], their length proved to be outside tolerance due to a debunching procedure plagued by microwave instabilities. An alternative scenario was then proposed, based on a series of bunch-splitting steps in the PS. The entire process has recently been implemented successfully, and beams whose longitudinal characteristics are safely inside LHC specifications are now routinely available. Variants of the method also enable bunch trains with gaps of different lengths to be generated. These are of interest for the study and possible cure of electron cloud effects in both the SPS and LHC. The paper summarizes the beam dynamics issues that had to be addressed to produce beams with all the requisite qualities for the LHC. 1 THE LHC PROTON INJECTOR CHAIN 1.1 Parameters of the LHC proton beams For LHC collider operation, three different proton beams are required: (i) the “initial ” or “commissioning” beam, permitting LHC physics during the first two years at a luminosity of 1033 cm-2s-1; (ii) the “nominal ” beam for operating the LHC at 1034 cm-2s-1; (iii) the “ultimate” beam, which is the foreseeable LHC performance limit at 2.5x1034 cm-2s-1. Table 1: LHC proton injector chain, nominal parameters