FCC-ee top-up injection

Name: FCC-ee top-up injection
Start: 2025-03-06T14:00:00+01:00
End: 2025-03-06T15:00:00+01:00
Location: No location set

Thursday 6 Mar 2025, 14:00 → 15:00 Europe/Zurich

66156014911

Yann Dutheil

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Present: C. Carli, Y. Dutheil, A. Lechner, T. Mori, G. Nigrelli, G. Roy, K. Skoufaris, S. Yue

The Optics Design Group aims to gather all inputs this year, including top-up injection.
Discussion scheduled for next week.
Close interaction with top-up injection will be addressed.
Goal: consolidate all necessary information by the end of the year for decision-making.

Oide-san supports maintaining the same optics at all four technical straights.
Ghislain prefers specialised insertions to decouple each technical insertion.
Some level of periodicity must be maintained, raising the question of chromaticity symmetry breaking and its effects.
Interest exists in having different optics at each straight; it is necessary for ttbar, but feasibility remains under discussion.
Careful consideration will be needed for both LCC and GHC.

A work plan is needed to compare LCC and GHC lattices.
Yann will propose a top-up talk at FCC Week and an IPAC contribution, including all WG participants in the IPAC author list.

Simulations using lattice 624 (to be added to Ghislain’s repo under 25.1_GHC).
Z-scan shows an optimum at -10 mm, improving survival rate.
Lower horizontal emittance growth with version 624 and z-offset.
Hybrid injection scheme results in lower longitudinal and vertical emittance growth.

Kyriacos observes that vertical emittance increase disappears for energy offsets <70% of the initial value.
Chromatic mismatch is questioned as a possible source of emittance increase.
Kyriacos did not observe improvement with matched chromatic optical functions.
From Sen:

Tracking results without beam-beam interactions.
Tracking with mean mode and zero horizontal emittance.
Follow-up discussion needed to align injected beam optics and optical parameters.

A new injection point was presented upstream of the quadrupole.
The new location has large d' and alpha, but its effect on effective septum thickness is negligible.
Agreement reached: the unique injection point will be placed 1m upstream of the quadrupole.

CI is conducting tracking and producing plots for injection efficiency and emittance.
Repository includes the new injection point change.
With agreement from all participants, the changes have been merged into the master branch.

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