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LNO section meeting on LHC DA, Dy and LEIR
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Europe/Zurich
6/R-012 - conference room (CERN)
Videoconference
LNO section meeting on LHC DA, Dy and LEIR
- Zoom Meeting ID
- 67341300731
- Host
- Rogelio Tomas Garcia
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Meeting on LHC DA, Dy and LEIR
News
Helmut says there has been a recent LHC background study group meeting. The observed doubling of muon rates in the very forward FASER and SND detectors this year is well reproduced by FLUKA simulations. The muons are also more energetic making backgrounds 3-4 times worse at the same luminosity compared to last year before the IR1 polarity change.
Rogelio says that the LHC is running well with a good production rate delivering already more than 50 fb-1. He sees 3 main optics options for 2025 and expects decisions with also depend on the possibility of an extension to 2026
i ) the possibility of reverting the polarity change in IR1
ii ) a polarity change in IR5
iii ) keeping the 2024 optics in 2025
and options to squeeze further towards 20 cm, possibly just in the separation plane as the following presentation from Sofia might suggest.
Dynamic aperture in the 30 - 20 cm segment, Sofia Kostoglou, slides
Sofia modeled the intensity, emittance, leveling (beta*, separation, crossing), luminosity and lifetime evolution of LHC fills. She illustrates that the model matches well the observed evolution for the recent fill 9905 and uses the model to see what could be gained in integrated luminosity by squeezing beta* from 30 towards 20 cm. A main limitation is the beam-beam (b.b.) interaction limiting the dynamic aperture (DA) to 5-5.5 sigma and the minimum realistic beta to approximately 22 cm. The predictions also depend on the turn around time and machine settings including octupole currents, chromaticity and b.b.wire compensation. Without considering limitations from DA in the 30-22cm segment, Sofia expects that up to an extension of 4 hours leveling time and 8% more integrated luminosity could be obtained. However, considering the DA limitation from beam-beam almost no luminosity could be expected from the 30-22cm segment as the beta steps would require waiting for the beam intensity decay. The DA simulation could be made closer to current fills by reducing chroma to 8, increasing octupoles to 400 Amps and reducing emittance to 2 um.
Rogelio says there is also a potential to increase the maximum allowed bunch population of 1.6e11 to 1.8e11 in 2025. This will increase integrated luminosity, but the luminosity gain from the 30-22cm segment would be reduced. Helmut asked if the b.b. model uses real or nominal sigmas and Sofia says it is based on nominal (2.5 μm emittance) sigmas.
It will be important to review simulations with the more realistic values of this year but also for 2025 with 1.8e11 ppb.
News on LHC Vertical Dispersion, Yannis Angelis, slides
Yannis reports on studies to improve the understanding of the observed vertical dispersion and in particular an increase of DY apparent between IR5 and IR6 for beam2 at injection. He also shows Dy measured in the HL-optics MD at flat top on the of June 6, which does not show a major increase for beam2 and a rather similar dispersion wave for beam1. Modeling with a main single source like a 9 mrad tilt of MQ.29R5 appears to not well reproduce the observations in Beam 1. However, a clear problem is observed in the Beam 1 segment-by-segment plots that needs to be corrected.
Rogelio expects that a good understanding requires further measurements. Of particular interest would be measurements at very different tunes as should be possible with the 60 degree phase advance MD that is now in the plan.
Update on LEIR optics, Felix Carlier, slides
Felix presents a recap of the measurements performed in 2022+2023, the current understanding. The beta beating increases with energy from 25% to 50% in the horizontal plane. A good reproducibility of optics measurements between 2022 and 2023 was found. The “weak focusing” of the bends is very significant in the horizontal plane for the rather small LEIR machine. The LEIR dipoles consist of 6 separate blocks of iron with a single continuous coil and a large wedge in the middle. Magnetic measurements and OPERA modeling including wedges would be important. Field maps are only available for the center of the blocks. The observed beta beating at injection can approximately be modeled with a thin quadrupole of 1.7% of the main K1L strength. Further optics measurements with improved control of orbit, sextupoles and chromaticity are planned for the heavy ion commissioning later this year and should help to further constrain the localization of error sources and improve the LEIR modeling.
Rogelio suggests using the MADX wire element to get an estimate of the role of the coils in the wedge without iron yoke.
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