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FCC-ee optics tuning WG meeting
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FCC-ee optics tuning WG meeting
Zoom Meeting ID
65518046965
Host
Rogelio Tomas Garcia
Alternative host
Jacqueline Keintzel
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Rogelio and Jacqueline reported on the news and the requests from the FCC week, the SAC meeting and the last FCC-ee design meeting. This is reflected in the slides in the first entry of the agenda.
Elaf Musaf, Tuning with SR
Adding SR worked nicely and DA is well recovered for 10 seeds! Without crab sextupoles the DA is better but vertical emittance is larger. This needs to be checked. Simone confirms that horizontal dispersion correction is harder and that the tails of the emittance are long with few seeds with very bad emittance. Either decide that getting 90% of the seeds successful is sufficient.
Yi Wu, Polarization with errors
Seeds with low polarization need to be recomputed with tracking as formula could be wrong. Polarization seems still good up to 100 um as Jorg argued that having 60% polarization should not change the polarization time to reach 5-10% (this would be interesting for a future presentation).
A major source of closed orbit search failure is the BPM misalignments (one has to use ealign, DX, DY; and twiss, CENTRE), with 50% of seeds failing to find closed-orbit. Rogelio recommended to attach BPMs to sextupoles instead of to quadrupoles (Elaf did not align BPMs according to quads, she might suffer from this too).
Spin tune shifts larger than target are seen for 50um or larger misalignments. Maybe further corrections will improve results -> Try to get lattices after tuning from Simone or Elaf.
Christian Goffing, BBA in SuperKEKB and FCCee
BBA techniques are applied to SuperKEKB data reaching resolution of about 50um in H and 3um in V (5 methods are tested). Adding extra 1um BPM uncertainty implies 50um uncertainty in V. The SuperKEKB technique seems to be the best so could not be improved. Rogelio recalls that the improvement proposed by Xiaobiao was to project the measured orbit to the expected orbit from the quadrupole misliagnment in the model. This filters BPM noise and should improve the result.
Patrick Hunchack, Chromaticity studies
GHC lattice has larger high order chromatic terms than LCC up to 5th order. Also the variation over working point scans is greater in GHC, while LCC is less impacted by tune changes. LCC chromaticities remain more or less unchanged even when using the resonance enhancing working point (0.2, 0.3). A fitting artefact could be the reason for larger values at .148 horizontal tune in GHC, which will be investigated. Future studies include amplitude detuning over various working points and the impact of linear chromaticity correction on higher orders.
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