Abstract
Operating at 6.5 TeV, the LHC surpassed the expectations and delivered an average of 66 fb–1 integrated luminosity to the two high luminosity experiments ATLAS and CMS by the end of 2018. In order to provide a continuous feedback to the machine coordination for further optimizing the performance, an automated tool for monitoring the main beam parameters and machine configurations, has been devised and extensively used. New features like the coupling between the two planes and effects of noise, were added to the numerical model used since 2016 to calculate the machine luminosity. Estimates, based both on simulations and on observed beam parameters, were reported fill-by-fill as well as in overall trends during the year. Highlights of the observations including the observed additional emittance blow up (on top of IBS, SR and elastic scattering) as well as additional losses (on top of the expected proton burn off) are presented for the 2018 data. Finally, cumulated integrated luminosity projections from the model for the entire 2018 data based on different degradation mechanisms are compared also with respect to the achieved luminosity.
Highlights
The high brightness 25 ns beams [1] produced with the Batch Compression bunch Merging and Splitting (BCMS) scheme [2, 3] were used for the 2018 run
Overall the emittances along the cycle are smaller compared to previous years of Run 2 [13]
Based on the results presented in [14] for the calibration Fill 7220, the agreement of emittance scans with the emittances inferred from luminosity is 5-20 % and the emittances from Wire Scanners (WS) [16] are up to 10-15 % lower than the ones extracted from luminosity
Summary
The high brightness 25 ns beams [1] produced with the Batch Compression bunch Merging and Splitting (BCMS) scheme [2, 3] were used for the 2018 run. Aiming to gain some of the luminosity lost during collisions, the crossing angle is gradually reduced (anti-leveling process) [4, 5]. The transverse emittance along the LHC energy cycle and the beam losses at collisions are discussed for the 2018 run. Intrabeam Scattering(IBS), Synchrotron Radiation (SR) and elastic scattering are considered for modeling the transverse emittance growth. 1.6 1.5 1.6 1.5 start of collisions 2.0 1.7 1.5 1.7 from the luminosity leveling and the crossing angle antileveling, in 2018 the transverse emittance coupling [10] was included in the model as an additional feature
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