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FCC-ee tuning WG meeting
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Europe/Zurich
A journal paper was suggested by Ilya to collect latest developments in tuning and this idea is supported by Leon, Michael, Xiaobiao, Simone, et al. More details to come.
From the actions of previous meeting Elaf confirmed that they will study long range misalignments.
FCC-ee tuning studies by Haocheng Xu (IHEP), Yiwei Wang
Studies apply errors first only to the arcs to the Z lattice. About 150 um for quads and 10-20 um to sextupoles assuming BBA. Tuning starts with sextupoles off. Optics correction is LOCO based for beta functions. Tilts of 100 urad and strength errors of 2e-4. 8 of 10 machine successfully corrected. Dx~ 0.1m, Dy~0.001m. Vertical beta-beating rms~11% and peak 150%.
Very good vertical emittance is achieved.
The horizontal orbit can be improved by using also main dipoles as orbit correctors. The vertical orbit slightly deteriorates at BPMs but this could be due to statistics.
Tune corrections stay to the 1e-4 level.
Gishlain proposes to fix BPM to sextupole instead of quadrupole. Haocheng sees in reality difficult to fix BPM to sextupoles but simulation results should be better. Barbara confirms that BPMs are double plane. Elaf asked if it was checked to start the simulations with full sextupole strength and indeed this gave problems finding closed orbit in some seeds. Coupling correction was same approach as LHC and Tessa (not LOCO, that is only for beta-beating). Rogelio asked if DA was computed, as it should not be too large due to the large residual orbit, but this is not the case. Results on this will come later but it is not so easy to progress due to other commitments and orbit should be corrected first. Any progress will be welcome. Rogelio asked if it is understood why IR errors could be added in the CEPC lattice but not in the FCCee lattice (that is in line with other FCCee studies). Number of IPs is only two for CEPC and beta* is slightly more relaxed but further details are not known. Gishlain mentioned that IR elements should be studied case by case.
BBA by Xiaobiao
The PBBA performance can be improved by separating the quadrupoles in groups for the modulation. Iterations and reducing modulation depth does not improve PBBA performance. Adjusting the number singular values did not help either.
An improvement is found by actually computing orbit at center of the quadrupole. The systematic error of PBBA seems to have reduced a lot: maybe few um but detailed plot is needed as this is seen by eye from the difference of the traget and result lines.
In P-QMS non-linear fits of kick received by beam versus offset are needed. Practical solution would be to steer beam towards center then applying BBA with a small range. Maximum systematic error is 30um in H and 10 in V in this case. This is the final resolution that should be assumed. For PBBA
In the future PBBA will be applied to sextupoles.
Non-linear optics studies and comparison, by Patrick
MAD-NG is used for resonance driving terms and anharmonicities calculation as it performs significantly faster than PTC. A detailed comparison of chromaticity and anharmonicities is presented. LCCO is typically better with some exception where the baseline outperforms LCCO.
Next steps is to find ways to optimize these non-linearities with MAD-NG to optimize DA and MA.
Jacqueline pointed out that crab sextupoles were slightly different, these could be made equal in the future. Gishlain asks for the change of the higher order terms with e.g. tunes and chromaticity.
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