Minutes and Summary

Main purpose of the meeting: VdM feedback and plans till TS1

LPC minutes 27th May

Introduction (Federico Alessio)

(Witold Kozanecki, Chris Young, David Stickland) The numbers stated were always excluding overhead which is why it was longer. For next year we will need to think about allocating more time or curtailing the program. The purpose of the comment was that either we need to allocte more time in the schedule or cutail the program. In the estimates there was insufficient time allocated for the time taken for the magnets to settle. This has now been corrected in the program to estimate the time. The experiments should discuss internally how much time they wish to request for the program in 2025.

(Catrin Bernius, Chris Young) It was clarified that the TCL6 radiation activation test will be done after 1-2 days or 1-2 long runs of stable beams with the new setting.

(Enrico Bravin) It was clarified that this wouldn't be extra validation after TS1 as a full validation will be performed anyway. If a new better configuration is found then the validation will be done with the updated configuration. This is why it is important to test it before TS1.

(Witold Kozanecki, Enrico Bravin, Tobias Persson) How does this knob of the dispersion at IP1 alter the halo. It changes the dispersion at both the collimator and at IP1. It should improve the dispersion for the whole ring. It would also be possible to use the one at IP5 to achieve a similar effect but the one for IP1 is that which has been found to be the best. These are all knobs that are part of the original design.

(Georges Trad) The MD program has shifted 1 hour earlier due to a request from RP to dump the last beam an hour earlier.

(Andres Delannoy) There is an ongoing issue with LHC Fast Beam Current Transformer and one of the CMS luminosity detectors is having an issue which means that there are jumps in the measured luminosity. However CMS should not be publishing the data from this detector but should be using one of the other luminometers. It will be followed up how this data appeared in the MASSI file.

(Tobias Persson, Gianni Masetti) The plan for MD11883 is to look at emmitance scans in IP1 and IP5 with the beamspot shifted in z. For this it is needed to have luminosity from ATLAS and CMS, and also it is desirable to have the z position from one experiment. ATLAS's solonoid will be down at this time so it is not ideal for them to provide it. For the MD period CMS should have the magnet available as they plan to ramp down during the TS. It will also be discussed offline if there could be a collisions in any of the other IPs to see if they could help. This will be done in stable beams with proton physics.

(Gianni Masetti, Jorg Wenninger) For the end of the TS why is there is uncertainty in the re-start time. This is because of large works on the Swiss electrical grid and the LHC chain is disconnected while this is going on to avoid glitches/spikes.

(Jorg Wenninger, Michi Hostettler) The LHCb curve follows very well now because the curve got updated to 1.5E33 which is what is currently being recorded while before it was 1.7E33. Exactly what should be put on this plot will be discussed offline. Note that this isn't a target but a prediction.

CMS (Gianni Masetti)

(Chris Young, Jorg Wenninger) It was clarified that the order is RP alignment, loss maps, then intensity ramp-up. The RP alignment will be done in ADJUST.

ATLAS (Catrin Bernius)

(Matteo Solfaroli Camillocci) This would require a pre-cycle so it is not quite as quick as you might think but can still be inter-fill, but it will result in a delay overall. It therefore would still be effectively a dedicated access.

(Maciej Trzebinski, Roderik Bruce, Chris Young) Last year the effects were seen to be larger than those predicted from simulation such that this motivates trying this. There are also BLM measurements that also show the 7% decrease only, rather than any more, when TCL6 is opened. Additionally the 2mm limit from R2E comes from the optics from last year and ideally with the partial-RP optics this should be tighter such that running at 2mm for a long time would need to be discussed. It was clarified that it will be the FASER side that will be opened rather than SND as SND have their emulsion in.

(Chris Young) It was asked if the damage that was recently fixed is due to radiation - yes. Ok, this motivates doing the TCL6 test soon.

(Maciej Trzebinski) It was clarified that the AFP beam-based alignment can be done partially in parallel to the CMS request for BBA and should be quicker than their request.

(Michi Hostettler) It would be interesting to try this at some point to see if we get better optimzation of the beam lifetime with the 12 bunches colliding. There isn't an objection to a test few fills so that OP can see if this is important or not, but in general they are useful for background studies and fake jets in exotic searches.

ALICE (Andrea Ferrero)

(Chris Young) The 3mm shift was not introduced as in the run preceeding when we were going to implement it, you were already at zero.

(Federico Alessio, Michi Hostettler) We want to make a plot using the MASSI files to check that the jumps seen in ALICE are also seen in ATLAS/CMS/LHCb such that we are confident that it is the RF that is making the effect rather than the drift of the crossing planes. The feed-forward for this drift was re-optimized last night. Some of the jumps that are seen between fills are not understood as they are not at the point where we expect something has changed.

(Jorg Wenninger) The drift in the last fills looks like it might be a drift during the beta* leveling. Therefore you should focus on the first point rather than the bulk of the data. What Michi has implemented last night should reduce the drift away from zero after the initial measurement.

LHCb (Elena Dall'Occo)

(Jorg Wenninger, Michi Hostettler) There were several instabilities when the magnet was switched last time. It would be better to do a fill without the full machine to re-optimize the collision planes as we could see a dump at the start of collisions. This could be coupled to the mini-loss map to be optimal but then it interferes with having the same conditions before and after the change. It would therefore be a short fill with a partially filled machine of several hours, or to make a very large separation to begin with and move back, but then you need to be careful with aperature.

(Jorg Wenninger) Before making a shift in x we will need to look at corrector strengths and also the aperature.

(Michi Hostettler) From DOROS we see a small drift in y but not a shift. Therefore the results from LHCb are not confirmed by the DOROS system.

(Chris Young) It has only been a couple of weeks since the last switch. For the rest of the year do you intend on many switches. It won't be a huge number -- not every two weeks. LHCb will feed back to their physics conveners that the total number of switches should be minimised, within the required physics goals. From the experiment they also want to minimise the number of magnet cycles.

(Roderik Bruce, Jorg Wenninger) If someone can check the orbit shift at the TCT then this can give an idea of the amount of freedom there is. It is thought that it should be similar to the shift at the IP. The exact numbers will be followed up offline.