CERN Accelerating science

Article
Report number	arXiv:2204.04616
Title	Impedance modelling and collective effects in the Future Circular e$^{+}$e$^{−}$ Collider with 4 IPs
Author(s)	Migliorati, M. (U. Rome La Sapienza (main) ; INFN, Rome) ; Antuono, C. (INFN, Rome ; U. Rome La Sapienza (main) ; CERN) ; Carideo, E. (U. Rome La Sapienza (main) ; INFN, Rome ; CERN) ; Zhang, Y. (Beijing, Inst. High Energy Phys.) ; Zobov, M. (LNF, Dafne Light)
Publication	2022-08-25
Imprint	2022-04-10
Number of pages	16
In:	EPJ Tech. Instrum. 9 (2022) 10
DOI	10.1140/epjti/s40485-022-00084-z
Subject category	physics.acc-ph ; Accelerators and Storage Rings
Study	CERN FCC
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.
Copyright/License	preprint: (License: CC BY-NC-ND 4.0) publication: © 2022-2025 The Author(s) (License: CC-BY-4.0)

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