Minutes and Summary

Main purpose of the meeting: Planning for August and September TS1/Special Run

1) Introduction (Brian)

Topics of the day: performance, expt. request in August, planning for Sept. Special Run, PbPb target energy.


Performance of LHC: LHC now reached an instantaneous luminosity of 1.8 10^34.
Further progress is currently limited by the heat load limitation (200W per half cell). The heat load is e-cloud driven and the machine is conditioning very slowly. 
Decided to lower bunch intensity and increase the number of bunches in order not to exceed the heat load limit.

Integrated luminosity: 6-7 fb-1, see plot on slide 6.  Last 2.5 weeks integrating ~0.3 fb-1 per day. Some fills exceeding 0.5 fb-1.

Reminder that ALICE should provide massi files.

Beam dumps: still mainly due to machine issues: only 5 out of 25 fills dumped by operators.
Turn-around time rather high, so probably better to have long fills.
Last 2 weeks: averaging 40% stable beam time

Action: Try to avoid access this week (unless strong reason comes up)
Action: Try to keep stable beams as long a possible (15-16h). No operator dumps during working hour (call to LHCb if the fill is still useful).
 
Upcoming filling schemes on slide 13.

Option with 36b could be interesting and give 10-20% more luminosity.
This option is preferred by ATLAS. CMS will come back with an opinion in a few days.
For this week, we will stay with 2400 bunches. Proposal to try out one fill with 36b (keeping 2400 bunches) to see the effect on the heat load.

Stephane: we should consider mixed scheme 8b4e - BCMS. This might give significant gains. To be considered.

Emittance scan strategy: see discussion in the round table below.

VdM/LHCf run plan unchanged.

Pb-Pb target energy:
Training quenches are becoming an argument to run at lower energy.
Decision expected at the LPC meeting in 2 weeks from now.

Next LPC meeting on August 29th.


2) TS1 preparation and recovery (JW)

To speed up recovery after TS1, propose to finish VdM setup before MD1/TS1: 1 shift needed.

If IP shift is requested, this will imply new knob, RP re-aligmnent, and 1-2 shifts of measurements.

Draft outline of schedule on slide 3.

Witold expressed worry of too long shift for some experts; JW said the detailed can be ironed out later.

Emittance scans: would be good to perform the ATLAS/CMS scans at same time; alternatively the LHC could complement with some machine emittance scans in the other IP. 

LHC dashboard vistar being decommissioned. Users should give feedback on which of the quantities on that page were useful to them.

Filling scheme same as last time.

3) Round table

LHCb (Manuel)

VELO commissioning news: slide 2/3.
Plan for the next weeks on slide 4.

Stable beams during working hours will be priority for the next weeks.
No dumps during day time (see action above).

ALICE (Federico)

Beam scan planned for this week, 0 - 17 Hz/microbarn

ALICE lumi variations due to orbit instabilities.
JW: cause not yet understood.

LHCf run: currently no collisions foreseen in IP2, but ALICE would like to take data for ZDC commissioning, so request to have some collisions.
Magnets ++, ~ +70 microrad crossing angle.

ATLAS (Joerg)

PU limitation: last time, TRT limitation above mu = 42.
Now, can operate safely at mu=54 (2100b) and 50 (2400b).

Heat load limitations of LHC: ATLAS is fine with current proposal, but total integrated luminosity should be main argument.

Emittance scans: see slide 4. For ALTAS, an emittance scan every other fill is fine. 15 points @ 10 seconds/point shortly after the highest mu of the fill.
Second scan at end of fill, to be dropped after ramp-up period.

Heavy ion running: slide 5. Preferred energy is the one that gives higher statistics. If all equal, 5.02 TeV is slightly preferred.
pp ref run: 350/pb (for 2nb-1 PbPb) – about 4x the PbPb NN-luminosity. Requires mu~5, assuming 2544 bunches. TBC. 

Comment from JW: pp ref run in 2017 was with 25ns beam. No reason for particular #bunches. But keep in mind that beta* = 3m.

Decision on energy: expected at the next LPC meeting(see above).

Action:
Emittance scan in a fill shortly after reaching beta*=30cm for both ATLAS/CMS at same time + one at the end of the fill (if possible).
ATLAS may want to skip some (ATLAS will call).


CMS (Andrea)

CMS taking data at 90% efficiency. Running at PU=52 is fine (some deadtime issues)

Filling schema during heat load limitation: for CMS, the preference is to have fills with higher number of bunches with lower intensity (accumulate statistics for b-physics data) 
Emittance scans preference of CMS: 15 point scan @10s/scan step, soon after beta*=30cm is reached. See conclusion above.

CMS Lumi Request for VdM run (David Stickland)