Minutes and Summary

Main purpose of the meeting: Plan for 2026; update on vacuum leak repair; ecloud studies

LPC 16 February 2026

Present (P = in person): Martijn Mulders (P), Chiara Zampolli, Andrej Gorisek (P), Eric Torrence (P),  Roderik Bruce (P), Lotta Mether (P), Filip Moortgat (P), Krystian Roslon (P), Matteo Solfaroli (P), Jorg Wenninger (P), Archie Sharma (P), Julia Negro (P), Sofia Kostoglou (P), Witold Kozanecki (P), Tomasz Bold, Juan Esteban, Brian Petersen, Dragoslav Lazic, Federica Oliva, Ivan Amos Cali, Flavio Pisani, Maciej Trzebinski, Riccardo Longo, Delphine Rivoiron, Mirko Pojer, Stephane Fartoukh, Peter Steinberg, Richard Hawkings, Chris Young, Valentina Avati, Andres Delannoy

LPC intro (Chiara Zampoli)

Slide 19 : Andrej emphasizes that for AFP no BBA was requested. Chiara acknowledges. (Roderik Bruce): we proposed to AFP that insertion to a distance of 10mm (at a beta* of 3.1m) would be comfortable. This is more than the 20-25 sigma that had been suggested by AFP before. It is now up to the AFP team to decide if this is still interesting for physics. 

Slide 20: The dates for the splashes obviously have to be updated now that the schedule will shift. Jorg: the machine checkout will shift but how many days is not yet clear.

Sofia: (regarding the schedule on slide 9 in case TS is shifted after Whit Monday) MD4 needs to stay with the high-intensity test as it will be integrated; it cannot be grouped with the other MDs before the TS. 

Update on the TCTPV.4R2.B2 vacuum leak repair (Matteo Solfaroli)

Chiara: Did you say before that the collimator was important because of the magnet flip in ALICE? Matteo: No the collimator is very important in general. There was a discussion about blocking one jaw, but no both are needed so that idea was discarded. 

Chiara: In your opinion, is it more probable that the delay is shorter or longer than 6 days? Matteo: I don’t expect it to be longer. It is a fairly standard operation, so unless there is an unexpected problem it should not take longer.

Jorg: it is a very non-standard vacuum section, which has a huge effect on backgrounds in ALICE. So the bake-out is important.

Chiara: how do they validate the bake out: by monitoring the pressure? Matteo: yes they carefully control the temperature and monitor the pressure. The goal is to hopefully reach similar values as in 2025.
Chiara: do we have other collimators like this? Matteo: yes – all 16 TCTs are in very similar conditions. 4 around every experiment. Plus a few secondaries. So about 20. They are all around 5000 cycles, and some are even beyond. 

Andrej: and they will all be replaced during LS3? Matteo: no that is the problem. But this is now being considered because this problem was discovered last year. 

Chiara: but the movement that was done on this collimator was not something special, right? Matteo: indeed, it is part of the standard commissioning and validation that we need to do. It was not a large stroke. 

Martijn: it is not possible to inspect these bellows beforehand to find a weak spot? Matteo: they are extremely hard to reach, and in any case you can’t see anything. The leaks are extremely tiny and you don’t know at what point of the bellow they appear, so no. 

Chiara: if any of them break this year, do we need again 6 days? Matteo: no, first, depending on what breaks where we have to see if we need to replace it. But the pumping and bake out would not take that long, as this vacuum sub-sector is one of the worst. 

Roderik: just a comment – there is a task force in place on the collimator bellows. The current baseline does not have a replacement of the collimators, and it is not clear how quickly this can be done; probably some time during Run4. We are trying to see if there is any way to get around this. 

Jorg / Roderik: unfortunately there is no way, or for sure no easy way to just refurbish the bellows. 

Brian: if you replace 2 collimators now, how many spares are left? Matteo: we used 2 out of 5 spares that were ready to be installed (V and H). In terms of spares we should make it until the end of the year, hopefully. 

Experiments magnets during the high intensity test (Lotta Mether)

Witold: what is the minimum solenoid field you need to suppress the electron cloud? (Lotta:) it is quite small. I think milli-Tesla, I can check. (Filip:) this is quite important because if CMS will switch off during the high-intensity test there will  still be a current in the solenoid to heat up the magnet, given a field of about 0.1 T [[checked later: 60 mT ]] . This is different from the MDs where we switched off the magnet completely and did nothing. Something to be followed-up. 

Lotta: ok, we will have to do some dedicated studies to estimate the effect on e-clouds also taking into account the configuration of the field. 

Andrej: on ATLAS side, we don’t believe the Toroid has to stay on, because it should not have any effect whatsoever. (Jorg:) I also believe that from past experience. (Witold:) the effect of the Toroid you can check because during 2 years in Run3 we had high-intensity physics fills with Toroid ON and Toroid OFF. (Andrej:) the ATLAS solenoid should be on, but for the Toroid we have some plans for commissioning a protection mechanism to consolidate it for the future. 

Filip: does this mean that during Run 4 and 5 whenever we have a problem with the solenoid you would have these e-cloud issues and dump the beam? (Lotta:) in principle yes. That is also why in the beginning of the run when we have longer scrubbing periods we request your magnets to be in non-operational state, to (Filip:) de-scrub properly (Lotta:) yes, exactly for this eventuality. This was requested for the beginning of Run3, but I don’t remember in the end which magnets were on and off. 

Jorg: in the last years we just had one or two days to scrub so then you don’t ask the magnets to be switched off. 

Chiara: what is the meaning of the parts in bold on slide 8? (Lotta:) those are in general effects that e-cloud would have especially near the interaction regions. We cannot say 1:1 that magnets switched off would cause this. 

Chiara: what is the difference between slides 9 and 10? (Lotta:) I looked at different pressure gauges, as marked at the bottom of the slides. 

Witold: wasn’t there a period a few years ago when CMS had lots of trouble with the Solenoid off during physics fills, in recent years? (Filip: yes, absolutely). We had it even off last year during the MD, which is the one Lotta used for her study. More extended periods happened during Run2, but that was at lower intensities. 

Chiara: so, now the point is to figure out if the small current CMS will have is enough to control the e-clouds, right? This could be a way to go. (Lotta:) yes. (Roderik:) could you make a test like that? (Sofia:) good question - maybe in MD1, would that be enough time to change plans for the high-intensity test?  (Julia:) Of course they would like to have an answer sooner than that. (Sofia:) so even if we find out in MD1 that it does not work, it is too late to change? (Filip:) no we have to find an agreement. The problem is that we lose 2 weeks in the schedule of LS3. (Sofia:) we lose the high-intensity test if this doesn’t work.. (Jorg:) all we have to do is scrub CMS first, but we don’t know how long this takes.  (Martijn:) with the magnet off (Jorg:) yes. (Roderik:) how easy is it to ramp down and up the magnet (Filip:) it is not nice, but can be done (Roderik:) and to put this current (Filip:) I need to check, as it might heat up the magnet. (Jorg:) you probably cannot do that with cryo conditions? (Filip:) we can probably simulate this effect by just putting a small current, not with the special heating solenoids. To be checked. Thank you very much Lotta for the results. Now we have some numbers to discuss.

CMS (Julia Negro)

Slide 2, on the request to have a few minutes of collisions with single bunch in loss maps fills (Jorg:) you get this for free. Many hours of it, with single bunches. 

Slide 3, on the request not to insert PPS during the high-intensity test in MD1, but only in June (Jorg:) yes, that is Ok. (Julia:) do you foresee a new alignment (in June) for the different energy? (Jorg:) yes. (Filip:) at the beginning of the 2 weeks? (Jorg:) yes we should. They are on single beams so we can do it from the beginning in principle. It is only one per type, so only 2 pots. 

Chiara: do you have a limit on the smaller crossing angle in PbPb (Julia:) not really. Smaller angles are fine. (Witold:) you have to be careful with satellite bunches in lead-lead. (Filip:) how low do you want to go? Not zero. (Roderick:) not zero, around a 100 or so. And 50 ns bunch spacing. 

ATLAS (Andrej Gorisek)

Chiara: can you provide a field map of the Toroid to remove any doubt? (Andrej:) not from the beampipe. (Eric: ) there are probably more stray fields from pumps in that area. We have many hours of data taking with the Toroid off, that would have shown the effects if any.

ALICE (Silvia Pisano)

No comments

LHCb (Flavio Pisani)

No slides. 
* We will do a magnet flip before MD1, and one after MD1, exact dates to be confirmed. 
* We are Ok with keeping our magnet on during the high intensity test. We’d like to avoid having to switch it Off and On again, to minimize the number of cycles. 
* Recommissioning activities are going well. We will be ready to close the cavern on Thursday, but I understand that we can do that on Monday. To be checked with the TC team, but probably we will do it on Monday then. 

Chiara: question for everyone: for the low-mu run – maybe I missed it, but does any experiment have a limit on the duration of the fill. 
* ALICE : no upper limit.
* ATLAS (Eric) : still discussing this. For us it is a computing issue, of having very large runs. We are investigating ways to change our run number efficiently. We are doing a test right now and will get back to you.
* LHCB (Flavio): as long as we are leveled it is fine. No upper limit. We are talking about 40h, not 80h long fills right?
* CMS: no upper limit. 

Jorg: we already made a fill of 36h. So we have a chance to break this record.