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News and LHC MDs
Meeting on News and LHC MDs
News / Introduction
Rogelio reports that the LHC is running well and that a lot of detailed work is performed as also visible from the presentations in this meeting.
News from FASER & SND background and hierarchy breakage, Giuseppe Werner, slides, Xavier Buffat, slides
Giuseppe reports on FLUKA simulation studies performed to understand the reasons for the increased muon backgrounds observed this year by the very forward FASER & SND detectors at IR1. The backgrounds originate in the collision debris and are therefore proportional to the luminosity. Roughly two times higher backgrounds are observed this year in spite of tighter TCL6 collimator settings (1.585mm compared to 1.85 mm last year). The simulations indicate that the increase is mainly induced by the optics changes in triplet region up to the TAN result in a re-distribution in phase space of backgrounds apparent as increase in the locations of FASER and SND. As a next step it will be explored if going to a horizontal crossing in IR1 will reduce the FASER & SND muon backgrounds. Optics files have already been prepared by Stephane Fartoukh and will be used for simulation studies.
Xavier reports on preliminary studies to better understand the currently observed hierarchy violation were losses on secondary collimators can exceed losses on the primary collimators in spite of the 1.5 sigma larger gaps used for the secondary collimators. There are indications that the increased losses on the secondaries are related to a non-linear distortion of the phase space at larger amplitudes and momentum offset generated by a combination of effects including vertical dispersion, the choice of the working point close to the vertical third integer resonance, beam-beam effects and the rather large Q’=20 used in current LHC operation. Reducing Q’ down to 5 units in operation appears in fact to improve the situation. Xavier mentioned that this reduction of Q' could also be foreseen for HL-LHC.
Rogelio comments that further tests are planned these days in operation including studies using IR1 on_disp dispersion knobs and the Q' reduction.
First results from the anomalous Dy MD, Yannis Angelis, slides
Yannis reports on recent studies trying to better understand the anomalous vertical dispersions apparent on beam2. It was planned to reduce the main quadrupole MQ strength by 10 % and to compensate using the trim quads. A knob was prepared for this purpose but appeared to result in a poor match. The choice for the measurement in the MD was then to reduce the MQ in ARC 56 by 5% using the main quads in the other arcs to compensate. Changes in dispersion were observed and will be further studied to see if they could be the result of effects like a tilted quadrupole.
Rogelio comments that he expects that using a 60 degree lattice with very different MQ settings will help to resolve the puzzle.
HL-LHC optics MD status, Riccardo
Riccardo reminds that the main goal of a series of MDs under discussion for the next MD session MD2, MD3 this year and later is to test, develop and optimize optics for RUN4 (HL-LHC). A new set of optics has been prepared in the MD2 directory and is currently under revision of Matteo to transfer these into actual machine settings. New features of these optics include the phase knob matched to IRs, a modified IR4 optics at injection to prepare for more favorable betas for the e-lens in case it gets installed, as well as quite different IR3, 7 optics optimized for collimation, some of which could already be of interest for 2025. IR1, 5 will have more minor modifications mainly rematching phases. Next steps involve implementation as machine settings for MD2 including collimation functions.
2024 LHC Optics measurements in the ramp, Sasha Jade Horney, slides
Linear optics measurements during the ramp showed that the beta-beating remains within 15% for both beams and that the trends during the ramp are similar to those observed in 2023. The role of the injection and flattop corrections during the ramp should be explored as some improvement to the maximum beta-beating during the ramp could be found.
Several resonance driving terms (RDT) were clearly visible at injection and during the ramp. The strengths of the f1020 driving term was measured for both beams during the ramp and appears to be similar or somewhat reduced compared to 2023. The positive effect ot the correction at injection is confirmed. It would be interesting to know if the small reduction of the f1020 during the ramp is expected and review how exactly the MCS are ramped with respect to their ideal settings during the ramp.
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