Minutes and Summary

Main purpose of the meeting: Upcoming machine tests and Run 3 optics

1) Introduction (Brian)

Reminder of the schedule. Schedule was reviewed middle of March but not changed since last year.
Pilot beam best maintained in week 39-40. Cavern closure maintained on 1 Feb 2022.

Pilot beams should include collisions for experiments (450 GeV —  stable beams — probably 3 bunches). 
The whole beam test would take 13-14 days.

Schedule to be reviewed again on June 7th.

List of topics for next LPC meetings:

- oxygen run approved by CERN management. Will need to revisit baseline plan (energy, need for pp reference runs, lumi goals, beam
parameters).
- other special runs (LHCf low PU run, high beta* run, VdM scans, lumi related tests, ...)
- optimal collimator settings for  AFP/PPS in Run 3
- further input for pilot beam test


Propose next LPC meeting on June 14th.
(no objections in the room)

Comments:

- Jorg: special day to discuss pilot beam test around end of June. 
- Manuela: would good to bring up again the idea of extending Run 3 to 2025. Would be good to get input from experiments and machine.
Would be good to discuss this in a future LPC.
Notes: there will be an LMC meeting in June to discuss these issues from the machine point of view.

 

2) Upcoming machine tests (Jorg)

- S67 is now starting to cool down (after short circuit repair). All other sectors are in some form of powering test.
 Good progress, as expected. 4 sectors in dipole training. Cryogenics is handling 2 quenches per day.
 Very fast recovery in sectors 12 and 45. S34 is above 6.95 TeV. S78 is a bit slower, but almost  6.75 TeV.
 Heading to > 100 quenches in S78. See slide 6.

- LHC-OP is now present in the CCC every day morning/afternoon. 1 shifter, so limited parallelism.
Beside powering
Access requests discussed at end of Monday morning powering meeting, Mondays at 9am.

- safety tests: slide 8. 3 already passed. Next one is LASS (June 4th) and beam DSO test (June 18th)
For 2 upcoming tests, all experimental caverns must be closed. EN-AA will take care of open shielding walls.

- beam test of TI2 and TI8 transfer lines, from 25th of June till 27th of June. OK from all parties. Details on slide 9.
Injection permits of ALICE and LHCb are required.
Contact persons: G. Trad or Jorg W.

- data exchange machine-expt transits through DIP.
OP contacts are M. Hostettler and D. Mirachi
Inspection of machine data sent to DIP reveals that changes have to be made for

Macine to exp:

Q to expts: are you using these data?
Please check and report back

Expt to macihine:
for changes, please get in contact with contacts.

Items to be checked: Slide 13


- Timing test: machine only on May 5th-7th
Proposal to have test machine + experiments: May 19th to 21st
Handshakes, interlocks, data exchange, ….
Q to expts: would that timeslot be suitable?

Comments: 
- Ann Dubrowski: please keep the  because for Run 3 we may do some correlations studies (beam halo)
- Federico: when will you know if the test will be synchronous (clock) or not? A: 2 weeks before test
- Taku: what does ALICE need to do for this test? A: green light to switch on magnet on and off again.
- Michael Rijssenbeek: when is good test for Roman Pots to test RP-beam interface?
A (Jorg): for AFP still interventions till August, so not before early September
- Comment from Mario D.: MPP dedicated to Roman Pot questions in May



3) Run 3 Optics (Stephane)

Update on beam parameters for Run 3.


- slide 2: baseline filling scheme is BCMS. In case of 30% more heatload than expected: Mixed scheme with some 8b4e.
This would imply reduction of lumi by 9%.
Bunch charge and emittance from LIU in table. But bunch charge limited to 1.8 10^11 p/b for Run 3 (still TBC).

- slide 3: two scenarios for emittance blow up.

- slide 4: beam parameters for these 2 scenarios, in both cases for 2022 and 2023/2024.

- slide 5: which beta* at IP1 and IP5 at start of lumi levelling at 2 10^34? (IT cryo limit):
beta* = 60 cm is right for 2022. Beta* = 1.2m is right for 2023/2024.

- slide 6: AFP and PPS: very large beta* dynamic range from 1m++ to 30cm:
pre-squeezed beta* = 60cm, with r_tele = 0.5 to 2.0 (beta* from 1.2m to 30cm)

- slide 7: crossing angle management in IR1 and IR5:
two options: 1) working at BBLR limit: slightly more complex but saving some percent in IT lumi lifetime and better conditions for PPS.
2) working at constant xangle of 320 mrad.
One should prepare for mixture of both.

- slide 8: digression for PPS: BBLR limit changed with previous LPC to accommodate external vertical crossing angle in IR8 for 2023/2024.
As it is not, BBLR limit probably slightly pessimistic for 2022. In all cases, need to be fine tuned.

- slide 9: xangle polarity reversal policy in ATLAS to preserve triplet lumi lifetime.
Proposal for Run 3: -/-/+ for 2022/2023/2024.

- slide 10: NEW: beam & optics parameters in SB, lumi profile and luminous regions for 2022

- slide 11: same for 2023/2024

- slide 12: which beta* at IP8 for sufficient leveling time in the range of 1.5-2 10^33?    A: beta* = 2m seems to be a good compromise.

- slide 13: crossing angle for IR8? Reuqest similar physics conditions for both LHCb polarities.
Solution found with the same rotation and adjust BP for both LHCb polarities, with vertical half xangle of 300 microrad @beta*=2m.
Rotation to be tested during MD in 2022 and implement in 2023/2024.

- slide 15: hyper-cycle in Run 3 for 2022 and 2023/2024.

- slide 16: optics files available on afs.

- slide 18: summary

Q:

- Gaelle: slide 11: main changes to before? slighly longer fills preferred. 
PU in 2022 already avg rather 40 something, not 35 as we were expecting.
Stephane: note that bunch-to-bunch variation could be large.
Gaelle: this was studied previously and probably not a problem.
Comment form Ilias: this will be a problem at the end of run.
- Jorg from ATLAS: at some point PPS squeeze with limited current decay due to Q6 problem?
A: No problem, only need 4 minutes additional time needed.
- Brian: slide 17: are these actual beta* values that will be deployed, or just intermediate steps?
A: something done with reasonable granularity. Linear interpolation in between matchpoints.
Every 20cm in beta*, you need a correction. Strategy of exact implementation still needs to be discussed at the LBOC.
So plots in slide10/11 will have some step functions. Can increase granularity of steps.
- Gianni: slide 11: this is for best case scenario, what about worst case?
A: plots exist and will be provided
- Jorg from ATLAS: different PU profile if running with MIXED filling scheme? A: no difference expected.





4) Round table of experiments:

- LHCb (Federico)

- LHCb happy with proposed Run 3 conditions and thanks the LHC team for the work and the constructive discussions.
 — strong preference for BCMS scheme. If conditions are limited, LHCb asks to investigate new boundaries to push up integrated lumi
 — LHCb agrees with the plan fo implementing the V crossing angle in 2023, after validation in an MD in 2022
 — LHCb agrees with a value of beta*=2m throughout Run 3. If leveling is exhausted

- pilot beam test: LHCb installation schedule very tight and challenging

Handhake/interlock test:
   software ok
   hadrware: should be ok too, TBC

TED shots: 
  — LHCb does not request them
      will participate parasitaically for sync check, sw interloacks and possibly CALO 
       Inj permit will be availalbe

Beam test:
   — LHCb wwould like to participate and record data at 450 GeV
   — useful for sync with LHC, time alignment of sub-detectors ,,,
   — no tracking detectors available yet
   — difficult to provide reliable measure of instl lumi.

Request to have collisions not concentrated in single 24h stint
Request to be able to inject gas in fashion similar to Run 2 while beam1 circulating


Q Brian: no yet decided how to level in 2022?
A:  will probably level on average number of PU
Stephane: last sentence on slide 2: could add a second step of leveling (e.g. at 1.5 10^34) if needed. But to be decided later.


- ATLAS (Trevor)

- collisions with PU beams

— desire to start with probe bunches, few hours to full shift
— then with nominal bunches giving a higher rate
— would be good ot have few hours in between

 - desire for beam splashes (still checking with RP)

- ATLAS DCS-LHC interaction is ready for LHC handshake dry runs
   — would need stable beams hardware signal to test STANDBY/READY transitions

- Any planned changes to DIP publication structure?
- Any planned …

- Run 3 beam configuarions and ALTAS:

— how does the beams spot size and mu chang as fucntion of time with levelling. (Answered in Stephane’s slides 11-12) 

— Flat versus Round: slight preference for flat beams

— mixed filing scheme:
strong preference for BCMS. Earlier studies to carry could be repeated….

— proposal for luminosity study: see slide 5/6/7/8/9: observed mangetic non-linearity/hysteresis problem. 0.5-1% effect on sigma_vis.
This issue is holding up the ATLAS Run 2 lumi finalization (vdM calibrations).
- proposed experimental procedure on slide 8. Cost of 2 to 2.5 hours of beam time.


Comment from Jorg: does not like probe bunch collision, prefers collisions with nominal bunches and then separate the beams if needed.
Comment from Jorg on VdM scan: keep in mind: largely non commissioned machine …6 sigma?? ... setup time will be much longer than scan time.
Can we get 1/2 day extra time for this?
Comment from Witold: 3 sigma per beam. Did in in 2018.
Comment from Stephane: 3 sigma at injection, this becomes quite some millimeters. MPP should check.
Comment from Brian: lumi study not a request yet, correct? A: yes, still collecting feedback. Should settle it before Jun 14th meeting.


- ALICE (Taku)

— no news on Run 3 configurations
— readiness for handshake and data exchange tests in May: will be ready
— ALICE interested in using TED shots for validation of new pixel detectors
— interested in beam test in 2 39-40:
   — needs SB, injection energy fine
   — pilot bunches ok (verification of det repsonse and readout), but prefer nominals (more data, alignment and track matching)

Comment (Jorg): TED shots can be repeated if needed. 
Q (Jorg) For magnetic field: is one polarity ok? Or need both?
A: both if possible



- CMS (Gaelle):

— data exchange and handshake tests
   - CMS ready, happy to find best moment. Warning ~couple of weeks in advance to make sure relevant experts are around.

— Beam test:

 — CMS very interested. Wants Stable Beams. Few hours would be useful (>=4h). Goal is to measure position of pixel det wrt. to beam spot position.
 — multiple periods if possible 
 — Splashes interesting (for calo, tracking off)
 — would like to know a rough idea of expected beam spot size


— Run 3: 
    strong preference for pure BCMS scheme
   average and peak PU and lumi is important to know


Q (Brian): magnet on? A: yes, that is the plan. Should be commissioned before. If any problem, will keep it off.
Q (Michael Rijssenbeek) : possibility to insert the horizontal roman pots? E.g. 2 cm instead of 4 cm? To do timing on the detectors? Possible?
A: Jorg: needs special discussion with collimator team and safety aspects?
Comment from Mario: if this is possible, imagine that also CMS is interested.
Brian: should be discussed in a collimation meeting.



Conclusions:

for handshakes: everyone seems ready
for beam tests: few periods (of order 4h of collissions) spread out over few days. In second week.
Need to converge in lumi measurement proposal before June 14th.