Abstract
The High-Luminosity Large Hadron Collider (HL-LHC) experiments will operate at unprecedented levels of event pile-up from proton–proton collisions at 14 TeV centre-of-mass energy. In this paper, we study the performance of the baseline and a series of alternative scenarios in terms of the delivered integrated luminosity and its quality (pile-up density). A new figure-of-merit is introduced, the effective pile-up density, a concept that reflects the expected detector efficiency in the reconstruction of event vertices for a given operational scenario, acting as a link between the machine and experimental sides. Alternative scenarios have been proposed either to improve the baseline performance or to provide operational schemes in the case of particular limitations. Simulations of the evolution of their optimum fills with the latest set of parameters of the HL-LHC are performed with β*-levelling, and the results are discussed in terms of both the integrated luminosity and the effective pile-up density. The crab kissing scheme, a proposed scenario for pile-up density control, is re-evaluated under this new perspective with updated beam and optics parameters. Estimates on the expected integrated luminosity due to the impact of crab cavity noise, full crab crossing, and reduced cross section for burn-off, are also presented.
Highlights
Ver 2A sub-harmonic RF system at 200 MHz is proposed to replace the existing 400 MHz accelerating RF system in the LHC
Part of the present RF system at 400 MHz is retained to provide the required voltage at the second harmonic to increase the operating range between 1.35-2.0 ns [2, 3]. It provides the possibility of recapturing the stored beam during physics to reach smaller bunch lengths (1 ns) or perform additional bunch profile manipulations. This system provides an alternative scenario for luminosity optimization to reach the same integrated luminosity goals of HL-LHC while mitigating the electron cloud effect [4]
The ability of the injectors to provide the high intensity is outside the scope of this paper
Summary
Ver 2A sub-harmonic RF system at 200 MHz is proposed to replace the existing 400 MHz accelerating RF system in the LHC. The main goal for a lower frequency RF system is to improve the capture efficiency between the SPS and the LHC, accelerate and store very high intensity and long bunches as an alternative to the present HL-LHC baseline [1]. Part of the present RF system at 400 MHz is retained to provide the required voltage at the second harmonic to increase the operating range between 1.35-2.0 ns [2, 3].
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