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FCC-ee optics tuning WG meeting
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FCC-ee optics tuning WG meeting
Newcomer Chritian Goffing as PhD with Jacqueline on BBA.
Jacqueline reports on the status of the IPAC paper. Few points still missing, mostly: latest updates from Simone, IP tuning from Satya, multipolar tolerances from Abid and some words on optics measurements.
A first naive simulation approach to vibration for the FCCee, Freddy Albert Poirier (LAPP)
The lab has been involved in vibration and GM studies for CLIC, ATF2, SuperKEKB. A global plan of the simulation is presented where GM waves are considered in the MADX simulations to substantiate a naive approach. A vertical plannar wave is used to apply the magnet displacements in the lattice.
The enhancement factor of the magnet displacement is computed for various wavelengths. This factor is larger for FCCee than for LEP (factor 4). This makes FCCee to be a very sensitive machine. Furthter studies have been performed selecting different types of elements.
An analytical model of the IP displacement is compared to simulations with good agreement.
With this model IP displacements are evaluated for the Midterm Report GM assumptions (as proposed by Tor). 10nm offsets at the IP seem to appear in few turns. Feedback system should require a frequency above 100Hz as mentioned by Oide-San.
Jacqueline asked how realistic is the model used. Freddy is not sure about how to address this, LHC model would be tight at some points to match the assumption.
The SuperKEKB GM sensors output the data in the webpage every hour. Oide-san asks about the difference in the IP shift sensitivity between V22, V23 and LCC lattices as V22 is the least sen sensitive. It is not understood why there are these differences between the lattices. Some analytical understanding would be welcome although there are no free knobs available to adjust this quantity.
Tuning simulation updates, Simone Liuzzo (ESRF)
Simone reports that he received a new lattice from Pantaleo with longer quadrupoles in the final doublet to minimize the effects from SR.
He has new results for the tuning of Oide's lattice with ramping both alignment errors and sextupoles, however even very slow ramp (5%) does not improve previous results.
These results seem to start deviating from Tessa's previous results as Tessa managed to perform optics corrections however pyAT optics corrections are not successful. It could be the fact that Tessa uses phase advance and coupling RDTs in the correction.
Jorg mentions that commissioning optics would help, and indeed this is planned. As a matter of fact the error ramp is an approximation of a commissioning a beta* squeeze sequence. Christian clarifies that sextupole ramp is performed and suggested to do simulations with larger than 70um for the errors in the arcs only.
Oide mentions that he could tune a machine with 100um errors using also optics corrections based on phase.
Simone suggests to add phase advance correction to his optics correction algorithm.
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