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FCC-ee optics tuning WG meeting
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FCC-ee optics tuning WG meeting
News: Overleaf document for the feasibility report not yet made available.
IPAC25 abstract on tuning presented by Rogelio accepted by the CERN management.
Elaf, Tuning studies with ballistic optics
Changing value of BPM-alignment-to-sextupole from 20 to 10um did not improve situation. This study concludes the preference to have the BPM attached to quadrupoles.
Dispersion free steering greatly improved the emittance in the first phase of commissioning at beam threading before BBA (100um errors in BPM-to-quad alignment).
pyAT gives slightly different DA than Xsuite for the ballistic optics. This needs to be understood and a new better ballistic optics is available and should be evaluated.
Oide-san wonders about the large effect of turning on the RF phase which maybe due to sextupoles being off.
Christian, BBA for FCCee
New technique to do BBA by K-modulation and orbit correction (with only related orbit correctors and using target orbit without kmod) with adjacent orbit corrector. Modulating 8 quadrupoles in parallel.
Performance of simulated BBA applied to Z (Kmod by 1%, BPM resolution 1um) gives a performance in the range between 4 and 9 um rms.
Change of magnetic axis witih quadrupole strength (3um at 1% kmod) to be included in simulations.
Kyriacos, Sextupole tuning with Xsuite
New tool developed to tune sextupoles to optimize MA in Xsuite.
After 160min of optimization a rather good optimization of V24.3 is found. Results are close to Oide-san's achieved MA, which is a great success. Of course, the tool can be run further and new improvements could be developped.
Jacqueline asks if this could be applied in the machine. Rogelio recalled that this was the case in KEKB and SuperKEKB, which Oide-san confirmed that manual optimization are performed fill-to-fill and it could be that this could be applied faster in the real machine than in simulations. Furthermore, this tool could indeed be used in the tuning simulation phase.
Jacqueline, required BPM resolution
QL, QY, QA and QS could need better BPMs resolution than 1 um (50000 turns at Z) in vertical area. Christian asked if actually for some of these quadrupoles the tolerance would not be so tight. Jacqueling replied that maybe for QL/QS but QA are actually next to sextupoles.
Oide-san asked if simulations with radiation could be performed. Jacqueline said yes, including also AC dipole.
Rogelio proposed to probe actual phase advances between defocusing quadrupoles (where sextupole pairs are placed), as currently probably focusing and defocusing quadrupoles are being paired in the simulations.
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