Minutes and Summary
Main purpose of the meeting:
First discussion on the LHC schedule post-recovery and status of crystal collimation for the ion run.
1) Introduction (Brian)
Weekly meetings for the next few weeks.
Next meeting: Sept 5th.
Performance of the LHC prior to RF disks bursting: peak lumi up to 1.95 10^34.
Added 4fb-1 in 9 days since last meeting. Total about 11 fb-1 in ATLAS/CMS.
> 50% stable beams also during day time.
Heat load: small gain by using 36b vs 48b. About 5% gain in luminosity.
Bunch intensity can also be pushed higher (currently up to 1.24 10^11 ppb).
Now 3-week break in schedule. Many activities to be rescheduled.
Now starting to discuss the schedule, see slide 10.
List of post-TS1 activities on slide 12.
Rende: bottom: about 2.5 days of MD1 to be added
Full program takes ~3 weeks out of ~7 weeks available between TS1 and TS2.
Remaining 4 weeks for p-p luminosity production, push of bunch intensity towards 1.4 10^11 ppb and for detector commissioning with collisions.
Is this sufficient time with p-p collisions? Would have to cancel all special physics runs and squeeze vdM run to gain even a week extra of p-p physics running.
List of post-TS1 activities on slide 14.
Possible Filling Scheme for LHCf Run on slide 15.
Comment from LHCf (Lorenzo): need a few non-colliding bunches.
Instrumentation Readiness for vdM: received input on BI instrumentation from BI experts, see slide 16.
PbPb target energy: request from ALICE to decide on final energy by mid September. Other spokespersons agreed.
Status of crystal collimation: see next talk.
Q&A:
David S. : what if postponing VdM and LHCf till later?
Brian: LHCf needs TS to install.
For VdM scan: valid question to know how precise we need to be this year.
David S. : when would the LHCb VELO be ready to measure ghost charge?
Federico A.: need 2 weeks of collisions before the VELO can be included in the VdM.
Then the VELO could take data (not with trigger, can be run afterwards, would take significant time to analyse data)
LHCb will ask to postpone the VdM for LHCb by 2 weeks, see later.
Michi: what about moving the VdM to the end of the proton run (after TS2)?
Brian: something to consider, but would have to move TS2.
Rende: could move TS 2 earlier if needed, but not during the weekend. Would be We/Thu/Fri.
Stephane F. : slide 12: also 0.5 day of floating MD to test the 2023 configuration.
2) Round table
LHCb (Federico A.)
LHCb requirements» for after TS1, see slide 1.
Requirements:
1) Pick-up commissioning data taking including full tracking system + VELO closing.
Need to take some useful data with full tracking system on and time aligned and must perform 1st VELO closing in pp collisions: in the highest priority list for LHCb for 2022.
a. Perform first step of VELO closing procedure as agreed with MPP. First Manual insertion to opening of 10mm. Then 2 fills (12bunches and 300 bunches).
b. Analyze the data to validate alignment and metrology (~ one week). VELO stays open during this period.
c. “Routine” (non-manual) insertion of VELO as agreed with MPP • 3 fills (12b, 300b and 1200b); to be confirmed once step c. is finished and validated.
2) The VdM in LHCb should be done with the VELO included.
Request that the VdM are kept at the same distance as they were from the last beams : ~2 weeks of data taking between restart and VdM ~ week 40.
We support the LHC MDs and we don’t request a cut back of MD days we would strongly prefer two blocks of MD days rather than a single block at the end.
3) In the remaining weeks of “physics run” we request as much Stable Beams during working hours as possible: request maximum priority to detector commissioning and isolated bunch(es).
ALICE (Sarah)
Interventions during TS1 (FIT, MCH, ZDC) on slide 1.
Initial plan to take data during LHCf run for ZDC commissioning (Magnets + +: -75 ur (int) + 145 (ext) = +70 ur )
ALICE Magnet OFF/OFF during the next ~ 3 weeks of NO BEAM
Brian: please re-asses your need for pp data prior to HI data taking (is 4 weeks + LHCf run enough?)
ATLAS (Joerg)
Constraints of scheduling a toroid-off muon-alignment run, see slide 2.
ATLAS would like to take some data for aligning the new NSW (100M events, an 8h regular fill with 600-2400 bunches).
Constraints:
ATLAS is fighting hard to keep the number of Toroid cycles to a minimum,
Can not take the muon-alignment data between TS1 and LHCf run
Can not take it after vdM run as the part of the vdM program after the LHCf run needs to be done with Toroid on.
Options:
1) Muon alignment run between LHCf and vdM. Preferred, if it works for the LHC and vdM program
2) Take it later. Would require another Toroid cycle (planned or opportunistic)
Considerations for option 1:
- “High lumi” before the vdM and (more critically) the 140b calibration run is not ideal
- Parts A (mag non-linearity) + B (length scale calibration) of the vdM program (planned before the LHCf run) do not require the toroid field (only solenoid)
- Less precise luminosity for LHCf run.
Brian: for LHCf, would be useful to know which level of luminosity precision is needed from ATLAS. To be followed up.
CMS (Gaelle)
Beam pipe and BPIX are positioned as expected
With present machine settings, the beam spot is a little more than 1 mm away from the BPIX centroid mostly due to a large, unexpected, offset (−0.8 mm) of the beams towards +x (inward) •
Y-position is perfect.
This offset is at the limit of what can be tolerated for the full Run-3 longevity of BPIX Layer-1
CMS strongly disfavors the option of keeping the beam spot unchanged throughout Run 3, risk of performance degradation of Layer-1.
Running with this offset in 2022 is however acceptable for the pixel detector.
Request maximal possible shift of the beam spot (up to 1.1mm) towards −x during YETS 22-23.
HI energy:
Request the highest possible beam energy (5.36 TeV) as long as this does not lead to lower integrated luminosity, otherwise prefer to stay at 5.02 TeV.
The energy should also be kept the same across the whole Run 3
Stephane: aperture will improve if you move outward in x, so not a problem. But may need to increase the crossing angle a bit. To be studied.
TOTEM (Mario)
1. Pixel tracking Roman Pots
Removal of old packages: first part of TS1 not possible (expert technician back on 02.09.) week 36 would be possible if access (planning: “OP tests (no access)”)
Installation of new packages: second part of TS1
Requires a beam-based re-alignment (~ 1 hour) for 3 pots. Can be parasitic.
2. Cooling leak in 56-220-F-H = XRPH.B6R5.B1 → will be fixed with detector package replacement discussed in (1)
3. Vertical misalignment of timing pot 45-220-C-H = XRPH.E6L5.B2
detector too high by ~ 2 mm
levelling operation takes only ~ 1 hour (done several times in Run 2) → first part of TS1
X-ray of RF-fingers might be needed … to be discussed in the next LMC.
SND (Richard)
Emulsion replacement going ahead as scheduled previously in TS1.
Currently using access to fix some issues.
3) Crystal collimation status (Marco d'Andrea)
Run 2 losses already close to quench limits. Up to 25-30% fills dumped on losses.
Upgrade of collimation system planned to ensure stable operation with ion beams
End of 2020: official decision to defer installation of TCLD collimators and 11 T dipoles after reliable operation at 7 TeV could not be demonstrated
Decision to rely on crystal collimation for Run 3 operation with heavy ion beams
Staged installation due to very tight schedule.
Crystals on vertical plane of both beams replaced during YETS 2021-2022.
Crystals on horizontal plane of both beams to be replaced during YETS 2022-2023.
Crystal collimation cleaning performance with proton beams cannot be easily translated into cleaning performance with heavy ion beams
Different dynamics when interacting with crystals. Different cleaning mechanisms.
Tests with proton beams still crucial to have early feedback on hardware and identify potential issues in preparation for ion run.
Key points to address:
1) Verify and characterize new hardware at injection and top energy
2) Confirm performance and stability of devices already tested in Run 2
3) Prepare and test energy ramp functions
Crystal collimators fully characterized. Optimal channeling identified at 450 GeV and at 6.8 TeV for all four crystals. New vertical crystals within specs, old horizontal crystals consistent with Run 2
Cleaning measurements performed with protons at 6.8 TeV. Improvement with respect to standard collimation comparable or better than in 2018.
Cleaning performance with protons not directly translated to Pb ions, but no strong indications to expect worse performance than in 2018.
Based on tests done so far, we are confident on the use of crystal collimation at 6.8 TeV.
Next steps:
1) Continue assessing cleaning performance and study how these results scale for Pb ions
2) Generate and test energy ramp functions
Main risks:
1) Detailed cleaning performance with ions, as well as beam lifetime and quench limit scaling, cannot be accurately predicted.
Possibility to step back in energy and/or intensity if dumps end up being too frequent
2) Risk that old horizontal crystals lose reference orientation.
Around a shift (~1 hour at injection + test ramp) to re-establish channeling and re-validation.
Very small risk that optimal channeling orientation of old horizontal crystals shifts outside of goniometer range.
In case it is decided to go for 6.37 Z TeV, we would still propose to use crystal collimation as baseline to improve cleaning performance
Brian: it seems that there is no objection to have the crystal collimation as baseline, independent of the choice of energy.
