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FCC-ee optics tuning WG
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FCC-ee optics tuning WG meeting
J. Keintzel and R. Tomas show the draft slides for the review.
C. Goffing shows news on the BBA for FCC.
The tune change from quadrupole modulation (all in the same direction) for BBA is similar for GHC and LCC, however, beta-beating is cancelled for GHC thanks to 90° phase advance per cell. With alternating modulation per quadrupole tune shift disappears, and LCC beta-beating is reduced, while for GHC it is increased drastically.
In the report with higher modulation amplitude the accuracy improves again. This is explained since at higher amplitude more seeds fail and so the average is smaller.
In GHC significant tails are found. Most of them occur for QF4 and for QF2, so they are not fully random. Taking a closer look at them, the corrected kick strength next to the modulated quadrupole is systematically shifted for huge part of the seeds, which could be the result that the error is not corrected locally, but rather by an orbit bump.
K. Andre presents news on the LCC tuning. The vertical emittance growth reported in the report is likely from chosing 90 MV RF voltage, which shifts the tune close to a synchro-betatron resonance.
He presents about the converter from pyAT to xsuite. 4D is considered. J. Salvesen comments that multipoles can also be thick. For EBS lattice beta agrees within 1e-6 and dispersion within 1e-9 without errors and star-fish plots seem ok (R. Tomas suggests taking a closer look). With errors errors increase to 1e-4 and 1e-5, respectively, for beta and dispersion.
For more recent tuning studies, he is ramping sextupoles in 3 steps. Crab sextupole is ramped at the end. No field errors are included. For MA he is now applying x and y offsets equally in sigma. BPMs in the IRs are next to sextupoles. CCSX/Y are no longer split and the octupole/decapole is outside of them. About 11 seeds failed or have very poor MA/DA. In general optics is better corrected. No strength errors are applied yet in the IRs. Using 50 µm in the FD (compared to 10 µm before), MA is in most cases still larger than 1%, so LCC IR FD tolerances could be a bit more relaxed. Larger than 50 µm, more seeds fail and emittance is large.
S. Liuzzo presents on the EBS restart. The mechanical alignment took about 6 days, and is the first time after 5 years. BBA took about 20h in total. The uncertainty is about 5 to 10 µm for BBA between 2 measurements. Sextupoles and octupoles are optimised using badger and xopt for injection efficiency and lifetime. All corrector strengths are lower after the alignment campaign. For the skew quadrupoles BBA K. Paraschou is working on it. For parallel quadrupole BBA a factor 1.8 is found, likely from the correction of the orbit.
D. Pio introduces her project as an intern, working for 2 months on optics measurements with an AC dipole.
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