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Start of Run 3 commissioning - Joint LNO-NDC
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Start of Run 3 commissioning - Joint LNO-NDC
Wednesday 27/04/2022 : Joint LNO-NDC meeting on the start of the Run 3 commissioning, with short news from the section leaders followed by seven presentations reporting about the first observations with beams.
LNO News, Rogelio :
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Minutes of the last meeting LNO meeting are on https://indico.cern.ch/event/1151913/ , please check. The LHC commissioning with beam started on Friday and progressed very well as also visible from the measurements already performed and reported in this meeting.
The dedicated sequence to open the collimators to the aperutre minus one sigma is a great improvement from Run 2 when a collimator expert had to do this operation manually. This is a clear joint success of the 3 teams in the preparation phase of Run 3 (OP-NDC-LNO).
Welcome to Daryna Pastushenko who joined us as trainee working on CLIC acc-models.
Javier Cardona who was previously at CERN in 2011 has arrived and started to work on the re-commissioning with first results reported by him in this meeting.
NDC News, Stefano :
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Minutes of the last NDC meeting, prepared by Frederik, are on https://indico.cern.ch/event/1141177/ . The collimation team is very busy in the ongoing commissioning with beams as also reported in this meeting.
After the Easter break and today's joint event, regular NDC meetings will resume Wednesday next week in the standard time slot, going through the list of actions prepared by Stefano for the NDC section.
In this particularly busy period, please make sure to prepare and send IPAC contributions as soon as possible. Pascal reports that two bibtex repositories have been made available on https://www.overleaf.com/9621589647stqhcqsbpbqz : ndc_mainbib.bib with citations to mostly collimation related papers prepared by Roderik and him, and non_linear_stuff_mainbib.bib prepared by Massimo.
Collimator alignment activities, Gabriella Azzopardi, slides
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Gabriella reported from the CCC, showing slides prepared with Bjorn and Stefano for the collimation team, on the observations made at injection energy in an eight hour shift on Sunday, and the first coarse collimator setup at flat top (without TCTs). Some minor issues with automatic alignment were noted and quickly resolved. The alignment with beam of left and right primary (TCP) collimator jaws revealed asymmetries, with for the TCP.C6R7.B2 an apparent +400 murad tilt of the left and a -700 murad tilt of the right jaw. This was communicated to the alignment team who, after the beam measurements, reported indeed that this collimator was out of specs according to their 2021 measurements. They are asked to intervene to fix the alignment during the access on Wed.
This topic could be included in a future presentation by J.F. Fuchs in a joint LNO-NDC meeting.
Aperture measurements in LHC Run 3 Commissioning, Pascal Hermes (for the collimation team), slides
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Beam based aperture measurements are performed at all main steps from injection to top energy to make sure that the machine aperture is as expected and protected by collimators. Pascal reminds how this is done using collimators and observing losses with the BLM monitors, with controlled beam blow up. In addition local orbit bumps can be used to provide further aperture information in selected (critical) locations. The aperture measurements performed in the October 2021 beam revealed an aperture restriction at 21L3 that was then in fact confirmed as buckled RF finger. Aperture checks were performed on Sunday at injection energy with coarse collimator settings and did not show any un-usual issues. Typically, values close to or above 12 sigmas are found for both beams and planes. Further measurements are planned today and the next days.
Linear optics measurements, Felix Soubelet (for the OMC team), slides
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Felix reports about the first RUN3 linear optics measurements performed at injection energy and after the first (immediately successful) ramp. The measurements showed that the injection optics is good and did not change significantly from 2021. Coupling was measured in the ramp. |C-| was trimmed based on the observations in the first ramp, and verified in a second ramp. The beta beating was measured at flat top, and found to be within 20 - 30 % peak beating as can be expected for the un-corrected machine. Local errors at the new top energy of 6.8 TeV appear to differ from what was measured in 2018.
Andreas Wegscheider showed additional slides highlighting that it is now possible to perform knob extraction from the control system. This already works using a python script and will soon become a standard feature of the online modeling (OMC) software.
Local optics corrections, Felix Carlier (for the OMC team), slides
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Felix shows results from the first local optics measurements performed in the interaction regions at flat top, with nominal beta* of 1.33 m in IR1/5, 2m in IR8 and 10m in IR2. Some changes from Run 2 but no critical errors were observed. More detailed measurements for the squeezed optics will be performed soon with k-modulation and will help to fine tune the local linear optics corrections.
After the meeting it was found that there was a deferred value assignment ":=" between left and right quadrupole triplet variables that impacts these results. Bug is fixed and reviewed results will be presented in the future.
Action and phase jump analysis, Javier Cardona, slides
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Javier illustrates the method of using action (kicks) from turn-by-turn beam position data to determine local quadrupole errors in the LHC interaction regions. The first application of this method in RUN 3 revealed some software issues (apparent as un-physical jump in the left arc of IR1) and appears to confirm for IR1/5 the trends also reported in the previous presentation (IR1 requiring less and IR5 more local corrections).
Non-linear chromaticity, Mael Le Garrec (for the OMC team), slides
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Mael shows tunes measured for momentum offsets DPP from -0.0032 to 0.0037, fitted using Q'' and Q''' with and without MCDO correction. He also shows first RDT (resonance driving term) measurements with an observation of the b5 resonance. Further analysis is planned. Mael said it would be nice to further increase the DPP range that appears currently to be limited by the coarse IR3 collimator settings.
Stefano sees possibilities to further retract IR3 collimator settings for measurements with pilot beams.
Stephane suggests to also measure with larger (H/V) tune split.
Ewen acknowledges the improvement from the dedicated sequence to open collimators.
Amplitude detuning, Joschua Dilly (for the OMC team), slides
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Joschua shows the tune spectra recorded for increasing kick amplitudes and first very preliminary results on tune changes with amplitude, that appear to be in broad agreement with measurements in RUN2 with an indication of an increase in the crossed term.
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