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