Summary of the single-beam collective effects in the LHC

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.