Impedance modelling and collective effects in the Future Circular e+e− Collider with 4 IPs

Abstract

The FCC-ee impedance model is being constantly updated closely following the vacuum chamber design and parameters evolution. In particular, at present, a thicker NEG coating of 150 nm (instead of previous 100 nm) has been suggested by the vacuum experts, and a more realistic impedance model of the bellows has been investigated. Moreover, also the transverse impedance has been updated by considering the same sources as for the longitudinal case. Therefore, the FCC-ee impedance database is getting more complete and the impedance model is being refined. In this paper we describe the presently available machine coupling impedance in both longitudinal and transverse planes, and study the impedance-driven single bunch instabilities (with and without beam-beam interaction) for the new FCC-ee parameter set with 4 interaction points (IPs). The results are compared with the previously obtained ones and a further possible mitigation of the beam-beam head-tail instability (X-Z instability) is proposed.

FCC-ee Collective Effects and their mitigation

“…Emanuela Carideo while in this study we considered the beamstrahlung and the collective effects due to the wakefields independently of each other. This self-consistency aspect has been investigated more closely in a study of beam-beam interactions [11,12].…”

Study of beam-beam interaction in FCC-ee including updated transverse and longitudinal Impedances

“…Further studies relying on both numerical simulations [7] and analytical analysis [8] have revealed that the longitudinal impedance may strengthen this instability. So different mitigation techniques have been considered [9,10] and parameter optimizations have been therefore performed to cope with the instability.…”

“…Following the design process of FCCee, the main machine parameters have been evolving and the impedance budget has been updated [11,12]. An accompanying paper of these proceedings is dedicated to impedance calculation and single-beam collective effect studies [12].…”

“…Following the design process of FCCee, the main machine parameters have been evolving and the impedance budget has been updated [11,12]. An accompanying paper of these proceedings is dedicated to impedance calculation and single-beam collective effect studies [12]. In this paper, we focus on the combined effect of beam-beam interaction and the updated impedance, taking into account both longitudinal and transverse impedances.…”

Studies of FCC-ee Single Bunch Instabilities with an Updated Impedance Model

“…In this paper, we focus our study on the single beam impedance-induced instabilities related to the lowest energy machine, which is most challenging from the collective effects point of view. In particular, for the beam dynamics simulations, we use the parameter list discussed in [3] and present an update of previously evaluated impedances and related instabilities [4,5,6,7,8,9].…”