FCC-ee top-up injection

Thursday Sep 3, 2026, 9:00 AM → 10:00 AM Europe/Zurich

participants :  C. Carli, Y. Dutheil. G. Nigrelli, P. Raimondi, K. Skoufaris, L. Valle 

 

• septum blade thickness
  • arguments discussed and agreement within participants to keep 2.8 mm as baseline
  • input from tracking studies and parameter scans will be critical to support further developement towards thinner septum
• Machine protection
  • present input from ABT planned for the MP workshop outlines general concept without specific solution yet established
  • possible strategy with passive absorbers in booster-to-collider and collider injection region similar to LHC 
  • Lina raises a point regarding fast RF failure at the higher energy mode and potential impacts due to large energy loss per turn -> will contact directly Angela (ABT contact for MP questions)
• booster to collider transfer
  • Pantaleo suggests that a symetric septa scheme (same device for booster extraction and collider injection) would allow cancelation
  • presently not consider as booster uses thicker septum but should be considered when errors will be explored
• collimation numbers
  • Giulia confirmed the Z-mode collimation scheme has TCS at 11sigma and momentum cut at 1.4%
  • implies BSC at max(11sigma, 1.4+0.3) is very large in the injection region -> need to iterate on the conventional injection bump amplitude required
• Lattice and frequencies
  • Present ABT injection repos use LCC 106.2, will wait for a review of the RF to update beam parameters
  •  Christian noted that ABP acknowledges the impact of beam parameters on injection, but these discussions currently remain within ABP and results will be communicated at a later date
  • Yann asked how this process should be handled so that requirements from the injection process are included. Christian confirmed the question is complex and is still under discussion within ABP
  • Despite other urgent activities Kyriacos has managed to conduct some simulations and will try to share results at a future meeting

9:00 AM → 9:20 AM thin injection septum consideration

• FCC-ee baseline: keep 2.8 mm direct-drive blade as the reference-design baseline. Pantaleo’s BTC slide assumes two 9.6 m septum dipoles,~0.140 T at ttbar and suggests a “hopefully 1 mm” thinner last part of the in-vacuum septum, but this is not yet an equipment-demonstrated baseline for a 304 us flat-top.
• technologies
  • direct drive : thickness of 2.8 mm is already thin. 
    lowering the field to an extremely low value (like a few tens of mT at the lower energy modes) does not necessarily make life easier, given the parasitic effects we start needing to consider when dealing with such low fields.
  • eddy current : 
    most common in light sources for ~1 mm thickness
    involves a much shorter pulse than the 304 µs flat-top currently required
  • Lambertson 
    1.5-2mm blade demonstrated at other facilities but limited experience at CERN and needs adjusting TL concept for vertical deflection
• Light sources examples

  • SPring-8-II: in-vacuum eddy-current , 1mm, 10 us half-sine

  • SLS 2.0: in-vacuum eddy-current, 1 mm wall, 12.5 us sine

  • HEPS: Lambertson septum, 2 mm

  • ESRF-EBS: in-vacuum eddy-current, about 3 mm blade, 66 us half-sine 

  • APS-U: pulsed direct-drive septum, 3 mm tapered blade, single-turn pulsed

• Conclusion
  1 mm should be kept as an R&D / upgrade option, but equipment baseline should remain at 2.8 mm under-vacuum direct-drive solution as it is considered a realistic solution to provide the FCC pulse length, leakage, impedance, vacuum, cooling, and machine-protection constraints (at the present maturity of the study). Further input on the requirement from top-up injection efficiency studies remain a critical input and should be addressed together with the various constraints 

 

Concept used for the FSR below 

9:20 AM → 9:40 AM Machine protection constraints

9:40 AM → 10:00 AM ABT repo structure

internal available

https://gitlab.cern.ch/abt-optics-and-code-repository/projects/fcc