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FCC-ee tuning
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FCC-ee tuning
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Helene presented the alignment issues for FCC-ee. Being the size of the machine the cost and technology driver. She presented the R&D plan and studies, which should be launched asap to provide technical proposals and a cost estimate. for 2025. But given the ressources situation, they might not be launched before 2029.
Tobias asked whether the CLIC approach was not applicable at least to the IRs. Helene replied that maybe size and different targets (linear vs circular collider) are an issue.
Felix asked if realignment of elements on the girder was planned. Helene replied that with a good design of the girder we should not need to realign elements inside girder. Maybe this will only be needed after transport (except if there is large local gradient temperature, etc.).
Andrea clarified that in ESRF the girders travel about 30 km, so it is not so short distance, maybe comparable to FCC-ee. Helene asked if the components of girder measured after installation in ESRF? After the meeting Andrea and David replied to Helene via email that in ESRF they did not realign any of the magnets on the girders after storage and transport as it was checked not needed.
Rogelio asked if interest of other labs. could be used to progress with alignment R&D, however Helene replies that also this progress would require CERN manpower to coordinate.
Helene also clarified to a question from Rogelio that the actual value of tolerances will not be the cost driver, being the size of the machine the main one.
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Andrea and Simone presented first experimental results in ESRF to tune lifetime after a sextupole strength is reduced by 50%. Good results are recorded but lifetime is not fully recovered. First simulations with FCC-ee show promising results to restore lifetime with a large error in an IR sextupole. Andrea experiences that FCC-ee lattice is challenging and sensitive (as expected).
Ilya expressed concerns on the granularity to control RF frequency (25Hz presented) and on power supply ripple (3e-5 m-2 quad changes reported). It should not be a problem to control frequency at Hz level. Power supply ripple in LHC is 0.1-1e-6 in relative terms.
Tobias asked if radiation was not included. Andrea replied that these are the first steps to probe the issues without radiation.
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Yi presented an effective model with 0.1um misalignments and subsequent quadrupolar corrections. This model has been used for polarization (Yi) and injection studies (Michael). Tessa commented that orbit correction could have reduced the peak ~1 mm orbit reported. Felix offered the effective model to the community. Rogelio asked how one could be sure that this effective model is effective enough. E.g. could the ~1 mm orbit peaks drive the polarization loss? Few more steps in tuning would be very useful.
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Jacqueline presented the last steps in understanding the decoherence with synchrotron radiation, amplitude detuning and second order chromaticity, pointing to an interplay between the later two effects not present in equations.
Jacqueline also presented first experience with Tessa's tuning codes. Discrepancies in the code requirements, issues with paths and a problem with the code after 3 hours will be checked.
Jacqueline clarified to Andrea that quantum excitation can be removed in SAD to avoid emittance build up.
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Ilya reported experimental progress with AC dipole in PETRA III and made a call for experimental proposals. They are also making first steps with tuning codes in collaboration with Tessa, ESRF and Jacqueline. This critical mass starts to look very promising to improve and further develop the codes.
Rogelio mentioned that progress with AC dipole in light sources is very beneficial for FCC-ee as this is one potential measurement technique. Probably next meeting could be devoted to this.
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Barbara presented impact of errors in the FCC-ee booster. Maximum tolerable misalignments without correction were 100um. Next steps will be to deploy correction schemes and see which corrections will be fundamental.
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