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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.

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Echo phenomena are well known in plasma physics and have been observed in accelerators in the longitudinal plane. Echo measurements are appealing since they allow the determination of small di usion coe cients in a relatively short time. In this paper we explore the possibility of observing transverse echos in an accelerator. The easiest way to create a transverse echo is to apply a dipole kick to the beam, followed by a quadrupole kick. The technical challenge lies in the application of the quadrupole kick. We consider two approaches for the quadrupole kick: a pulsed quadrupole that is excited for a few turns and an AC quadrupole that is excited for a couple of hundred turns. For both cases simulations are performed and the technical feasibility i s i n vestigated.

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