Summary of the single-beam collective effects in the LHC

Abstract

SUMMARY OF THE SINGLE-BEAM COLLECTIVE EFFECTS IN THE LHCBerg, J.S.; Bruening, O.; Caspers, F.; D'yachkov, M.*; Morvillo, M.; Ruggiero, F.Single beam collective effects can limit the performance of the LHC and, together with parasitic losses, impose constraints on the design of the components of the LHC vacuum system. Because of the large number of bunches in the LHC, coherent losses and multibunch instability rise times generated by the impedance items can be rather large. For example, the vacuum chambers of the main experiments can lead to large parasitic losses and a continuous feedback from the impedance calculations during their design process is desirable. We first summarise the current status of the impedance model for the LHC and estimate rise times and threshold currents for different instabilities. In a second step, we discuss possibilities of controlling these instabilities, using feedback systems and Landau damping. Abstract Single beam collective effects can limit the performance of the LHC and, together with parasitic losses, impose constraints on the design of the components of the LHC vacuum system. Because of the large number of bunches in the LHC, coherent losses and multibunch instability rise times generated by the impedance items can be rather large. For example, the vacuum chambers of the main experiments can lead to large parasitic losses and a continuous feedback from the impedance calculations during their design process is desirable. We first summarise the current status of the impedance model for the LHC and estimate rise times and threshold currents for different instabilities. In a second step, we discuss possibilities of controlling these instabilities, using feedback systems and Landau damping.

A study of the coherent beam–beam effect in the framework of the Vlasov perturbation theory

“…The damping rate (≈ 6s -1 and ≈ 8s -1 respectively) is sufficient to suppress the resistive wall instability, whose growth rate at top energy (with account of the magneto-resistive effect) is expected not to exceed 5s -1 [17]. It is possible to enhance Landau damping by tuning the chromaticity negative.…”

The HL-LHC Accelerator Physics Challenges

“…For the nominal LHC a systematic review of single beam collective effects was given in Ref. [30], and a comprehensive updated summary in Ref. [31].…”

On Transverse mode coupling instability in VLHC

“…Resulting impedance budgets for low-field and high-field options of the VLHC (some parameters are taken from [2]), 3 TeV low-field injector with C = 34 km (with L 86m) and for the LHC [8] are presented in Table 1. Table 1 also presents the threshold bunch population for these machines at their injection energies where the TMCI is expected to be more dangerous.…”