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FCC-ee optics tuning WG
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FCC-ee optics tuning WG
News: IPAC24 tuning abstract to be submitted by Leon.
FCCIS output, Jacqueline
Request to have organized lattice and parameter structure. Ghislain will take over the optics repository.
Need to decide on the baseline optics by FCC week 2024, June.
Progress on the dipole design for the booster. HFD lattice option also considered for the Booster.
FCCIS finishes in Nov. 2024 but some deadlines are earlier, as Booster design, etc.
Xsuite is continuously being developed, easy to start with.
BBA performance is simulated to be between 10um and 30um resolution.
Trim coils options presented in 3 flavours, to be evaluated by tolerance estimates.
BPM resolution is estimated to be 1nm (it is possible to average over many bunches and turns).
BI requested specifications from beam dynamics.
Barbara mentions that Booster deliverable should be moved to October 2024.
Ilya comments that tolerances below 100um is not easy and commissioning optics should be also used. Leon provided optics in the past but without optimizaing sextupoles. Oide-san will work on a new relaxed optics. Simone adds that this will add another factor 2 in the number of lattices,
Tuning studies for LCCO and V22, Simone
All correctors are included in the Sextupoles in LCCO lattice for simplicity. For the V22 correctors are placed at quadrupoles.
LCCO lattice has no crab sextupole.
Long range misalignments are studied, showing e.g. a ~1mm tolerance at 10km, which is much tighter than currently assumed.
File as output by Michael tool is used very comfortably. Maybe worth asking survey to provide similar tables. The misliagnments provided by Michael make lattice fully unstable. We can only cope with a factor 10 lower errors.
In the tuning simulations only 10um errors are considered. 1 seed out of 10 fails for LCCO and vertical emittance is very poor (~9pm). Oide's lattice has better vertical emittance, which could come from having used more correctors. Dispersions at the IP are large for both optics.
Using the long-range errors (reduced with a factor 10 -> order of max 100-200um excursion) gives very poor performance in tuning for both lattices. Slightly worse for V22 (Oide's) as more seeds fail. Various attempts to make the emittance correction work for large errors failed. Suggestion from Pantaleo is to add more correctors.
Ramping the sextupoles iteratively with corrections helps a lot if orbit correctors are at quadrupoles but not if orbit correctors are at sextupoles!
Oide-san comments that the failure of tuning with the long-range errors could depend on the orbit correction performance. Indeed orbit after correctoin stays at ~100 um, while it should have been possible to improve it.
Maybe the high frequency in the long-range errors is still too large. Simulations should be run only with low frequencies to answer this.
Orbit correction for Polarization studies, Yi Wu
In general good orbit correction guarantees good polarization but only for alignment errors below 100um, where various seeds fail and others perform clearly worse.
Long-range errors could be problematic here as they could reach few mm. Furthermore the studies do not assume BPM misalignments (neither Simone assumed BPM systematic errors).
Jacqueline asks for polarization time. Yi replies that she will study this.
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