Performance and Operational Aspects of High-Luminosity LHC Operational Scenarios

The High-Luminosity LHC (HL-LHC) is the upgrade of the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) aiming at the full exploitation of the collider, with operations scheduled to start after 2025. Using the latest sets of parameters, the performance at the two main interaction points (IPs) of the HL-LHC baseline and main alternative operational scenarios is evaluated at both nominal and ultimate levelling (corresponding to levelled luminosities of $5\times 10^{34}~\text{cm}^{-2}\text{s}^{-1}$ and $7.5\times 10^{34}~\text{cm}^{-2}\text{s}^{-1}$, respectively). Realistic simulations of the evolution of the optimum fills are conducted with the purpose-developed Levelling program, which takes into account the effects of beam intensity burn-off, synchrotron radiation, intrabeam scattering, and crab cavity noise on emittance growth, in conjunction with a step-based luminosity levelling. Numerical computations of the luminosity can be implemented assuming a q-Gaussian bunch longitudinal profile -a realistic description based on observations in the LHC-, as well as with possible time offsets in the bunch position. Results provide an insight into the operational challenges of each scenario (e.g. the number of optics to be commissioned), and detailed characterisations of their corresponding luminous regions around the IPs -a valuable input for studies on the detector efficiency under a wide range of configurations. The latest estimates on the performance of the different HL-LHC operational scenarios in terms of yearly integrated luminosity and effective pile-up density comprise the central results of this work. The latter is a new and complementary figure-of-merit introduced in collaboration with the ATLAS and CMS experiments characterising the expected detector performance based on the integrated average distribution of events around the IPs. In the case of the baseline, it is shown that the goals of the HL-LHC project are met (yearly integrated luminosity above $250~\text{fb}^{-1}$ and $320~\text{fb}^{-1}$ at nominal and ultimate operation, respectively). The found effective pile-up densities of $0.80~\text{mm}^{-1}$ and $1.20~\text{mm}^{-1}$, respectively, constitute the references for comparisons with the alternative scenarios. In order to understand the effect of each parameter and to guide possible future optimisations, an extensive series of sensitivity studies is conducted for the baseline. Operation at the ultimate energy of $7.5~\text{TeV}$ and several scenarios for a high-luminosity LHCb experiment are also explored. Lastly, a correction scheme of the long-range beam-beam effects -which might limit the machine performance- using local corrector magnets is also proposed.