Choose timezone
Your profile timezone:
FCC-ee optics tuning WG meeting
→
Europe/Zurich
FCC-ee optics tuning WG meeting
Zoom Meeting ID
65518046965
Host
Rogelio Tomas Garcia
Alternative host
Jacqueline Keintzel
Useful links
Join via phone
Zoom URL
S. Liuzzo presents first simulations when using phase correction (phase between BPMs, tunes, dispersion and RDTs) vs LOCO for V22 at 45.6 GeV. He reminds that using pyAT and MADX for orbit gives the same results, so difference should stem from different optics correction techniques. Using phase correction the beta beating is corrected better. However, DA is not improved. Simulations, where alignment errors larger than 40 µm are applied fail since orbits are in the order of several mm, which cannot be corrected. R. Tomas suggests that T. Charles applies her optics correction techniques to the seeds presented here. Following a question by F. Zimmermann, S. Liuzzo answers that emittances are not optimized with his technique. In the future it should be defined which DA is considered sufficient. With SR DA is shrinking drastically. R. Tomas suggests to try switching off crab-waist. K. Oide suggests to always include radiation in DA studies. F. Zimmermann suggests to check 6D off-momentum DA.
E. Musa presents updates of tuning studies with phase, horizontal dispersion, tune and RDT and vertical dispersion correction using pyAT. With 100 µm applied misalignments in arc quadrupoles and sextupoles a vertical emittance below 1 pm is achieved. Large DA (only 4D) is achieved. Applying 50 µm in the IRs, additional to 100 µm in the arcs is more challenging and about 60% of the seeds fail, investigations are ongoing to apply dispersion free steering. In the future SR should be included. S. Liuzzo suggests to also use his seed for comparison.
S. Sai presents a comparison between using LOCO and phase correction for the V22 lattice at 45.6 GeV with radiation. 35 µm are applied at all arc quadrupoles and sextupoles. Sextupoles are ramped in steps of 20%. Chromaticity is corrected at the end. Beta-beating and dispersion is corrected better using phase advance correction. IR errors and IP tuning knobs will be included in the next step. S. Liuzzo suggests to also compute DA. S. Liuzzo explains that LOCO is based on the simulation of a measurement, while for the phase correction the twiss files of the perfect optics is used. He, therefore, proposes to include a more realistic simulation of measurement error when using phase correction. R. Tomas explains that for the LHC the error on the phase advance is in the order of 1e-3. He reminds that simulations by J. Keintzel suggest that this could be achieved for V22 with reasonable BPMs (resolution a few µm). K. Oide suggests to include design tapering.
K. Skoufaris presents sextupolar phase advance tolerances and impact of Ground Motion (GM) waves on the DA for a thin lattice. S. Liuzzo comments that this could possibly impact the non-linear optics. A beating beating of a few per mille is introduced using this technique. DA is 38 sigma without DA and with SR and tapering 17 sigma. With a phase error of pm 5e-4rad 15 sigmas are achieved. With -1e-3rad DA is reduced to 7 sigma. This suggests that the BPM resolution in the IR should be tightened by about a factor 10. F. Zimmermann suggest to correct the tune. K. Oide suggests to extend the plot to show the reduction of vertical DA better. For the GM only sextupoles or additional quadrupoles are misalinged according to the table in the MTR. For uncorreleated GM (rather element vibration than GM) with 100 nm oscillation amplitde DA remains at 17 sigma. The worst seeds give a beating beating of 7%. For correleated GM with 1 Hz and 100 nm amplitude the DA is 17 sigma. S. Liuzzo suggests to envisage a possible optics correction feedback to correct optics distortions from GM, in case orbit feedback will not be sufficient. F. Zimmermann comments that 100 nm vibration amplitude seems rather pessimistic. F. Carlier suggests to inlcude orbit correction.
A. Hussain presents updates on multipolar tolerances for IR and arc magnets in V22 in 6D with SR and tapering at 45.6 GeV. K. Oide suggests to not perfrom DA analysis at the IP.
- a4 random/systematic error in arc sextupoles are to ~ 36/25 units.
- a5 random/systematic error in arc sextupoles are ~ 30/30 units
- b5 random/systematic error in arc sextupoles are more than ~ 36/25 units
For the ttbar lattice studies have also been performed and are similar or larger than Z-lattice. R. Tomas suggests to perform similar studies for LCC lattice at Z-energy.
J. Keintzel presents updates on SKEKB. Sudden Beam Losses (SBL) occur several times per day for both rings, but more often in LER. During SBL a pressure burst is observed, which could the the cause or result of the SBL. The current working theory is that the clearing electrodes in the wiggler sections is demaged, dust particles fall down and interact with the beam, leading to loss of a large fraction the beam is lost within 1-3 turns. Installing a knocker could reproduce SBL 3 times. However, it could be that strong SR leads to evaporation of particles. Beam lifetime for colliding bunches is small and further reduces as number of bunches increases, which could point to e-cloud or wakefields. A vertical kicker is installed in HER, used to perform optics measurements with and without 40% crab waist. The data with large vertical kicks does not show damping, which could be a sign of impedance wakefields with chromaticity.
Two comments from Frank:
1) for SBL vertical oscillation signal might not be real, but just reflect the beam loss, if signal is offset x bunch charge
2) maybe the difference between fewer and many bunches is due to electron cloud or interplay of electron and beam-beam in case of many bunches ?
There are minutes attached to this event.
Show them.
