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FCC-ee optics tuning WG
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Europe/Zurich
18/3-008 - CLIC Meeting room (CERN)
FCC-ee optics tuning WG meeting
Actions:
- Sign switch of multipoles summary --> Table shared by R. Tomas: https://docs.google.com/spreadsheets/d/1DsW98Y8pwO7ic_VTeHbckpjzve7Z3FlyELz7Z2cQ4Q8/edit?usp=sharing
- Simulate failure of correctors and BPMs
- Larger roll error of BPMs up to 1mrad --> News presented today
- Repository for tuning result seeds --> To be followed up to have one repository for tuning and tuned lattices (S. Jagabathuni, J. Salvesen, J. Keintzel, K. Skoufaris, etc)
- Max BPM to quadrupole alignment --> more studies to be done
News:
- Meeting with alignment regarding long-range: --> Seeds to be shared by Jürgen and Vincent
Next meetings:
- 08 September 2026: special for SuperKEKB
Christian, H corrector configuration for BBA
Recently it was brought up the possibility to use the full dipole as orbit corrector. This has implications on BBA as the distance between the quarupole and the center of the orbit corrector shifts. First estimates show that within 200cm separation we are within ~12um resolution. For longer separation it is required to use a mixture of orbit correctors to correct orbit from quad, which would imply larger errors in BBA. This was seen in the LHC beam tests.
First estimate of this effect when using the dipole as H orbit corrector would imply extra ~20um error in BBA. This is a clear degradation but it could be OK as it is only in the H plane. To be further studied.
Wietse, a3 correction
The location of the missing sextupoles at QF3A in the arcs could be used to place a3 correctors.
At Z energy using 216 a3 corrs is found to work with a max k2l of 0.04 m^-2.
This solution could be complemented with few correctors at the DS. Half of the QF3A slots could also work.
At tt energy the effect of a3 is much lower and easier to correct with weaker correctors, probably due to phase advance, betas, etc. Hence these a3 correctors will be shorter and/or weaker than normal sextupoles.
MA is mostly restored at Z energy, but not fully, probably from second orders from a3.
a4 induced RDTs is observed. Skew octupole locations are to be explored.
Hence, a3 dipole errors and correctors can be already included in tuning simulations as these new elements will also generate optics distortions via feeddown.
Patrick, Coupling measurement errors with titls
Introducing BPM titls in simulations, analyzing via OMC3 software one obtains the expected uncertainties induced in the coupling measurement.
Estimates show that in the arc 1mrad BPM tilts give few 1e-4 error. IR error was larger by a factor 10 hence this would be further studies.
To realize the 1um random 100 bunches could be used.
To be discussed how these values should be included in simulations.Maybe by separating IR and arc.
Kevin, Updated tuning simulations
BBA and BPM tilts are studed with updated dipole errors.
Concerning BPM tilt error up to 400 urad simulations converge without much impact.
For now 500urad and RDT error of 1.25e-3 in RDT are considered.
Removing QF3A orbit correctors has some effect on vertical orbit and emittance (also f1001). -> Best recipe is to keep this corrector.
For the option having the H corrector in the full dipole, 20 um extra H BBA should be studied.
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