LPC meeting summary 07-12-2020 - final

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Minutes and Summary

Main purpose of the meeting: Discussion of the machine configuration for Run 3 (proton-proton).

Introduction (B. Petersen)
LS2 schedule rediscussed at end of October: decided to keep start date of Run 3 on 1st Feb 2022. Earlier start date now excluded.
11T magnet installation postponed.  Beam test will be in week 39-40 of 2021. LHC will be in YETS-like state from week 41, 2021 onwards till start of Run 3.
Injectors will run till mid-November 2021. Plan will be reviewed again mid-March 2021.
Special runs during Run 3: 
- low PU run for LHCf in 2022
- if beam energy high enough: high beta* run for TOTEM and ALFA/ATLAS. Tentatively scheduled for 2023 to leave enough time for preparations.
- potential oxygen run: currently not in MTP, accelerator studies on hold. LHCC received letters from cosmic ray community supporting an oxygen run.
LHCC recommended at least preparation for this option in Run 3. Discussed in RB last week: CERN management will follow up on options for oxygen run.
- possible short 900 GeV pp run for LHCb He-gas injection 
Q (Stefano): can you inject if SMOG and VELO not completely closed?
A (Federico): see discussion in last MPP meeting (LHC topics). Will be done with VELO 5mm open and also SMOG not fully closed.
Still possible to reconstruct vertices with efficiency similar to Run 2.
Request from Stefano to LHCb: once you have a full plan, please come back to us so we can check aperture etc.
LHC Powering tests (J. Wenninger)
Will start powering in January. See schedule on slide 2. Short circuit found in S81, so being warmed up again. This delays powering test in this sector by at least 4 weeks.
Powering tests coordinated by M. Solfaroli and A. Apollonio. Evolution can be followed at
Will prepare weekly status summaries on LHC machine coordinator page (
LHC-OP will be present in CCC from January onwards. CCC presence initially limited, see slide 4. Ramp up to 3 shifts/day in September.
Dates of DSO tests on slide 5: Powering DSO tests start on 8th of Jan, next one is RF DSO test on 18th of Feb. 
SPS extraction and transfer line DSO test on March 19th, 2021. This requires closing of IP2 and IP8, so is agreed with ALICE and LHCb.
LHC Access Safety systems tests on 4th of June. Beam DSO tests on 18th of June.
Machine configurations for Run 3 (pp) (S. Fartoukh)
Disclaimer: work in progress.
Filling scheme: baseline is BCMS scheme (smaller emittance than standard 25ns scheme). Backup scheme is to insert some 8b4e in BCMS scheme to lower head-load.
Limitation of what SPS can produce: max 1.8 10^11 ppb in 2022, up to 2.1 or 2.3 10^11 ppb (BCMS beams).
Limitation of what can be swallowed by LHC: 1.8 10^11 ppb.
Emittance growth during ramp: assume scenario of 10% and 50% growth. Leads to two parameter sets, see slide 4.
Beta* range in ATLAS/CMS: see slide 5. Beta* of ~1m is right for ~ 1.6 10^11 ppb in 2022. Beta* of ~1.2m in 2023-2024. 
In case of intensity limitation in 2022 (1.4 10^11 ppb), we can do 60cm with a moderately enlarged crossing angle.
Crossing angle in IR1&5: two main options. One is to work at beam-beam limit. Advantage is 5% saving in IT lumi lifetime and better physics conditions for PPS.
Other option: constant X-angle of 320 murad. Probably less extra losses at beginning of SB. Prepare for both options at start of Run 3 (or mixture of both).
X-angle polarity strategy for ATLAS: vital to preserve triplet luminosity lifetime in Run 3.
Proposal to have -/-/+ for 2022/2023/2024 (or -/+/- if there are advantages for FP runs). Triplet dose expected 25MGY at end of Run 3 (vs. maximum limit of 30 MGY).
Request for feedback from experiments (forward detectors etc.)?
LHCb: which beta* at UP8 for sufficient levelling time in the range of 1.5-2 10^33?
See plot on slide 9. Beta*= 2m seems reasonable.
Crossing angle in LHCb: two main options: one is large H external crossing angle,
other is V external crossing angle after dedicated rotation. Request from LHCb to keep similar physics conditions for both LHCb polarities.
Solution found with same rotation & ADJUST BP for both LHCb polarities with vertical X-angle if 200 murad at beta*=1.5m. Need for MD in 2022 to confirm this, so only
foreseen for 2023.
FP experiments: ATLAS/ALFA and CMS/PPS.
Very large beta* dynamic range. Large variations expected for transport matrix from the IP to the RPs, unless beta* levelling in tele-mode.
Telescopic optics proposed: 2 scenarios, see slide 12.
Scenario 2 has telescopic optics before flat top arrival. This has improved MO efficiency for Landau damping and aperture preservation in the ramp (avoids complexity).
Proposal is to deploy the anti-telescope at E~4.5 TeV.
Hypercycle for Run 3: two scenarios proposed, see slide 14.
Latest news: in Run 2 a so-called PPS squeeze was requested to further maximize the normalized dispersion at the RP, through a reduction of the Q6 current down to 200A at constant beta*.
However, Q6 current reduction takes so long that arriving at FT in scenario 2 with optimal PPS conditions seems impossible.
This leads to new proposal, see slide 16 (introduces mini-squeeze of < 5 min possibly combined with LHCb X-angle rotation).
Previous estimates on levelling time (10-11h) and optimal fill length (14-15h) still hold.
Next steps: update and validate the Run 3 optics. Commissioning strategy to be defined.
Action: All FP experiments should check their compatibility with the proposed scheme.
Q (from C. Schwick): is levelling to low mu with beam separation still possible in Run 3?
A (Stephane): yes
Q (Brian): how will the luminous region change if you do the proposed levelling sequence? 
A (Stephane): can change by few cm’s. Can make plot of this.
Also requested later by K. Lantzsch.
Action (on Stephane): produce plot of luminous region 
Q (Witold): why is there no problem in CMS for IT radiation dose?
A (Stephane): because of vertical crossing. Most of debris are pi+ and the Q1 on outgoing beam always defocusses, so less problems in vertical plane.
Feedback from experiments
CMS-PPS (M. Deile):
1. efforts of machine experts to implement an (anti-)telescopic squeeze are very much appreciated.
2. lumi levelling along beam-beam limit curve (X-angle, beta*) is already studied and found to be ok. However, TCT collimation scheme is needed that minimizes RP movements during stable beams. 
Studies in Collimation Working Group still ongoing (interrupted due to COVID).
3. Slight change of BBLT curve is new version is not a problem.
4. The initial pure X-angle levelling is also fine.
5. in general, a mixture of small and large X-angles is advantageous since it covers a mass range from small to large.
Operating at fixed X-angle would not be favoured by PPS.
6. PPS would like to remind about last year’s request for a TCL position scan during an MD to explore the possibility of opening them further.
This is important for the high-mass acceptance.
LHCb (F. Alessio)
High impact of COVID on LHCb LS2 activities.
Installation schedule of LHCb extremely tight, leaving very little time for global commissioning.
Will not be able to use full detector in beam test. Still useful for commissioning though.
Proposed mitigations: anticipate as much as possible; parallel activities as much as possible; define minimum set of “absolutely necessary” steps. Then:
Request for interleaved mode of commissioning during initial LHC commissioning: a few periods of time (10%-20%? 4-6h/day?) without beam to exercise powering up and to let detector experts intervene in caverns.
2022 commissioning plan with beam, see slide 4.
Ideally would like final physics running conditions before the second large data taking period in 2022.
Request that MD to try vertical crossing angle comes rather early, around first Technical Stop (June?).
No activities planned underground during this end-of-year break.
Comments from J. Wenninger:
1. Commissioning starts on 15 of Feb., so you have an extra 2 weeks for commissioning.
2. 4-6h per day downtime is a lot. That would mean 20% extra commissioning time. Maybe a few nights/week. To be discussed later.
3. no quite beams foreseen, only stable beams.
4. X-angle MD … complicated procedure (including collimator settings, retune collisions, ...) … better to do this a bit later, like in September. 
Comment from Brian: 
Request for interleaved commissioning scheme to be discussed not only with LHC but also with other experiments.
Follow-up by email:
in a follow-up email, Federico clarified the following points:
- slide 3: "10/20% (4-6 hours/day)" --> "to few nights/week"
It wasn't meant to be a heavy request, what is available, we'll take it
... :).

- slide 7: "Final running conditions..." --> "Vertical crossing angle is still strongly requested to be in operations before nominal data taking period in 2022 (LHCb step 4, ~end-of-summer)." 
 Ideally we'd like to assess the outcome of the MD early on - as early as possible but still not too early if that prevents to have a meaningful MD. 
ATLAS (K. Lantzsch)
Run 3 beam configurations:
Change of sign of crossing angle is ok for AFP.
Also levelling of X-angle as well as levelling of beta* is fine, provided approach to insert RP’s as discussed during the last collimation WG meeting.
Need further discussion on this (Roderick confirms there will be meetings dedicated to this in January). Data for calibration will need to be gathered during BBA.
Request to have high beta* run as early as possible. 
Comment from Jorg: unlikely to happen in 2022 (maybe a few tests).
Activities during end-of-year break:
Daily safety tour.
ATLAS annual safety test on 21 Dec.
ATLAS Evacuation test via CSAM on 31 Dec. 
On-call activities if necessary.
ALICE (T. Gunji)
Beam optic for Run 3: no changes requested compared to Run 2
Planned activities during end-of-year break:
No specific plans. Only regular tours of experiment, every second day.
CMS (G. Masetti)
End-of-year break activities:
Daily safety tour with 2 persons.
Maintenance of UXC55 crane for 1-2 days, on first week of Xmas break.