Emittance Evolution in the LHC: From Injection to Collisions

The emittance of the LHC beams when arriving in collisions is a key parameter for luminosity. Hence, the emittance of the beams from the injector complex needs to be preserved as well as possible throughout the cycle for maximum luminosity. Moreover, due to the V/H crossing scheme in IP1 and 5, non-round emittances yield different luminosities for ATLAS and CMS. Such a difference was e.g. observed in 2016 proton physics operation. This contribution analyzes the emittance evolution throughout the LHC nominal cycle in 2017. The emittance growth from injection to collisions is studied and the different emittance measurements are compared. Reproducible bunch patterns are shown and differences between the operational beam types (BCMS, 8b4e) are highlighted. Also, the roundness of the beams and the impact on the ATLAS to CMS luminosity ratio is assessed.