Minutes and Summary

Main purpose of the meeting: Planning for the rest of 2022, in particular the ion test period

Introduction (Filip Moortgat):

• An updated version of the 2022 plan was shown
  • The next 12 days should be focused on luminosity production if todays VELO insertion successful
• There has been good luminosity production in the last two weeks despite MD period and VELO insertion tests
• The VELO insertion was tested successfully with 300 bunches on Friday
  • a first test on Wednesday showed small drift, but iw was not related to the motion system
  • the Friday test was fully successful with vacuum and temperatures looking good
  • during the VELO tests, ATLAS and CMS have tested running at different pile-up settings
• Thursday saw a successful test with a hybrid filling scheme (mixed 8b4e and 48b trains)
  • the machine saw a 17% heat load reduction, even though bunch current only decreased 4%
  • with the hybrid scheme it could be possible to increase the bunch intensity to 1.5-1.6x10^11ppb
  • feedback from experiments is requested before switching to such a scheme
• For now, the LHC will continue to run with 2462b using 36b trains at mu=54 in IP1/5
  • it was noted that a 5% increase in pile-up, results in 2% integrated luminosity for long fills
  • with this filling scheme, the pile-up is any case limited to mu~58 due to triplet heating limit
• Switching to a hybrid scheme would likely require AGK change to fit in another 100b and match the current filling scheme
• vdM planning page has been updated after discussion in LLCMWG last week
  • still open for feedback from experiments
  • have to consider what to do in case of poor machine availability as we need vdM data and therefore could need more time
• It was stressed that the ion test is primarily to prepare for the 2023 physics run and not to accumulate physics data
• SND needs to exchange their emulsion walls as they are limited to ~20/fb from the high muon rate
  • would like to have 5-7 hour access in early November to replace it
  • November 4 is not optimal from scheduling as it would be followed by a short luminosity period and then MD2
    • one could advance MD2, but then the vdM period start is not optimal
    • November 3 might be also be option (confirmed by SND after the meeting
  • a concern was raised for later in Run 3  where SND could require up to 4 replacements per year
• Gianni Masetti asked about the pile-up target for the next regular fills
  • For CMS the exact value is not too important as long as CMS is below 58
  • He therefore asked that if CMS luminosity is higher than ATLAS, it should be leveled on CMS, not ATLAS
  • Jorg Wenninger did not want to flip to the highest one automatically, but it was agreed that one would use the one that was highest after optimization at beta*=60cm
• Witold Kozanecki asked if in the mu-scan fill after the vdM scans, ATLAS could be separated to 5sigma right after collisions are established to minimize activation
  • Jorg Wenninger did not see an issue with this
  • Witold also noted that ATLAS would like to do an additional fast mu scan in the crossing plane, but this requires a detailed plan to still be worked out

Planning for ion beam test (Roderik Bruce):

• The plan is for a test over 2 days (including 0.5 day of contingency)
  • will limit intensity to <3x10^11 charges/beam and use standard p-p cycle to minimize setup time
• The plan is to start with tests of slip-stacked beams and the crystal collimators so that they might be used during stable beam
• The slip stacking test will start with short train of 8 bunches with 50ns separation
  • could later try to use 4x8b but seems unlikely
• The crystal collimation test should demonsrate the channeling of the new crystals and improved cleaning efficiency
• Stable beam is planned with collisions in all experiments
  • plan two stable beam fills
    • the first fill would be single bunches as in Xe-Xe run with 4 non-colliding bunches used for loss maps before Stable Beam is declared
    • the second fill will use slipped-stacked beams and some indivs
  • the standard pp cycle at 60cm (IP1/5) will be used, but the crossing angle at ALICE will be changed in order to have acceptance for the ALICE ZDC
  • if the crystal test is successfull, would propose to insert them as primary collimators in the stable beam fills
  • the validation will be light due to the low charges and have already discussed been with MPP
• Several filling schemes are under consideration
  • ALICE will be prioritized for number of collisions as they ware penalized by the large beta* from the p-p cycle
  • for the fill propose to use 20b_8_16_8_8 (4 non-colliding bunches are used for validation)
  • for the fill with trains have two option:
    • 20_2_18_2_2 (trains only for ALICE, INDIVs for everyone else)
    • 20_8_19_8_2 (trains for ALICE/ATLAS/CMS, INDIVs for LHCb)
  • if the intensity from injector is low, could add more indivs
• It is assumed that each stable beam fill is ~5 hours long
  • this would give ~0.1/ub for ALICE per fill
  • ATLAS/CMS could get up to ~0.5/ub except in the 20_2_18_2_2 configuration of if they are leveled
  • it was noted that there are large uncertainties on the luminosity predictions as the beam parameters are very uncertain
• Some optional activities are under consideration
  • check if the ALICE ZDC acceptance is fine at 100urad
  • measure beam-beam effect of the 50ns trains
    • ALICE IP is likely not very useful for this, but IP1/5 could be used in end of fill
  • end-of fill test of IR2 TCLDs
    • still TBC if there is enough luminosity to see a BLM signal
• Federico Ronchetti noted:
  • that starting the stable beam in the middle of the night is not ideal
  • it might be possible to interleave a regular p-p fill, but it is a bit early to over optimize the schedule
  • ALICE will check if a test of the crossing angle dependence is needed
  • ALICE dipole should already have the correct polarity
• Brian asked the experiments to come back with their needs for commissioning during the ion beam test
• After the meeting ALICE agreed that they are ok with sharing a train with IP1/5 if IP1/5 are luminosity leveled.

Round table:

LHCb (Federico Alessio):

• The VELO closing is still being finalized with some debugging still on-going
  • plan to do regular VELO closings after the insertion has been commissioned
• With VELO closed, LHCb wants to start SMOG2 commissioning
  • this is being coordinating with the vacuum (VSC) team
  • they will inform CCC ahead of any gas injection
• For the vdM scans:
  • with the VELO closed, LHCb will be able to provide ghost charge measurements in addition to performing the luminosity calibration
  • there is still an on-going discussion on aperture limitation during the vdM scans
    • there is only 15sigma aperture with vdM optics
    • might not be able to fully close which would affect ghost charge measurements
    • possible solution from Ilias and LHCb vdM experts, to be followed up
• Plan to do mu-scans up to mu=7 once luminometers calibrated
  • LHCb will also take some extended data at various (high) pile-up values
• Foresee to test emittance scans in LHCb after the vdM scans are done
  • the procedure has to be worked with LHC-OP as it needs to be done with beams still separated
• Some magnet-off data-taking is also planned before or after the vdM scans
  • no constrains from LHC OP as long as they are warned well ahead of time
• For the ion test, LHCb would like to have a few colliding bunches for ion run and to do SMOG2 injection
  • Roderik asked what gas density will be used - this will be followed up by Federico

 
ALICE (Federico Ronchetti):

• ALICE is still trying to do several high rate runs for TPC scans
  • two runs have been done so far and might go as high as 5MHz in the coming weeks
  • ALICE might switch off their luminometer for some high rate fills and ask to level on BRANL2 instead
    • the BRANL2 looks well calibrated with the ALICE luminometer

ATLAS (Joerg Stelzer):

• Switched the online luminometer source on October 10, giving 1% higher luminosity
  • this does not affect the Massi files
• Have updated Massi files retrospectively with change in calibration constants reported several weeks ago
  • reduced the luminosity for the early runs significantly
• ATLAS currently stops publishing luminosity when the DAQ system is stopped
  • this is not ideal as it is used for leveling
  • it might be possible to have run standalone, but some technical issues remain to be discussed
• Would like to have emittance scan only every second fill and only at start of fill
  • will call CCC to inform them in each run during ramp
  • Jorg noted that the machine needs scans in both ATLAS and CMS to be useful for them
    • to be followed up with LHC experts
• ATLAS need a bit more time to understand impact of mixed filling scheme, particularly on a low-pt multi-jet trigger
• Some concern was raised regarding pushing intensity as the pile-up limit is still mu=55
• It was noted that the AFP temperature would rise to 55-60 degC at bunch intensities of 1.5e11ppb
  • will have to look at the vacuum behaviour to see if this will be a problem
  • it is planned to add a cooling system for next year
• For the ion test period, ATLAS is interested in having 50ns bunch trains for their testing

CMS (Gaelle Boudoul):

• No issues found in mixed filling scheme, so no objection to switch to mixed filling any time
• Jorg Wennninger expect to increase bunch intensity in steps of 0.05e11 ppb for further bunch intensity ramp-up
• See strange oscillation every 1-1.5 hours in beam 1 background
  • source is not understood
  • repeats across fills and is seen in multiple sensors
• For coming 1200b fill would like to mu=35 in CMS (post-meeting, request also extended to 600b fill)
  •  should be possible with offset leveling
  • ATLAS would like to stay at mu=54
• It was requested than any changes related to beam configuration are also reported by email and not just mattermost