2022 Operation

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trobbins
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Re: 2022 Operation

Post by trobbins » Fri Aug 05, 2022 12:44 pm

Here's hoping they get stable beams with 2100b. There seem to be a few UFO endings.

tomey36
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Re: 2022 Operation

Post by tomey36 » Fri Aug 05, 2022 11:09 pm

Anyone have a summary of how commissioning has gone so far. Any changes to their expected beam performance? It’s a lot harder to find info than in past runs. Just based off observations it seems there are a few cobwebs they needed to clean out.

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trobbins
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Re: 2022 Operation

Post by trobbins » Sat Aug 06, 2022 7:27 am

Certainly slower than the April schedule anticipated:
https://indico.cern.ch/event/1152484/co ... 202022.pdf

M.
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Re: 2022 Operation

Post by M. » Sun Aug 07, 2022 1:49 am

Yes, a bit behind the initial schedule due to the various problems, including 8 training quenches during operation, 1 UFO/beam induced quench and some trouble with the RF.

UFO rates at the beginning of the run were back to the levels of early 2015, clearly de-conditioning w.r.t. the end of Run 2, but that was expected due to the thermal cycles. So the UFO dumps do not come by surprise. Rates are already going down again.

2100b incoming next week if all goes well. Then we will see how much cryo can cope with, there is still significant heat load from electron cloud that needs to condition down before filling the machine completely.

A few public plots: https://bpt.web.cern.ch/lhc/statistics/2022/

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Re: 2022 Operation

Post by dukwon » Sun Aug 07, 2022 10:29 am

Are we really behind schedule? It says 1200b on 4th August, and we were already at 1900b by then.

I heard that the trouble with RF on Friday night was almost enough for them to abandon the night shift, but it seems to have been fixed in the end, albeit continuing on 1900b instead of 2100b.

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trobbins
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Re: 2022 Operation

Post by trobbins » Sun Aug 07, 2022 12:11 pm

Thanks for the link to the public plots. Yeh that Cryo Status summary plot certainly shows some locations that still heat up significantly more than others.

I guess 25ns_1935b_1922_1602_1672_192bpi is colloquially referred to as a 1900b fill even though it seems partially loaded by 1602 and 1672 ?

M.
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Re: 2022 Operation

Post by M. » Sun Aug 07, 2022 12:14 pm

Indeed, let me put it that way - there is contingency in the schedule to anticipate problems during the commissioning. We were 1-2 weeks ahead at times, most of which has been "lost back" in the meanwhile.

The RF holds for the moment, but the problem will need to be investigated further next week. During the commissioning there were a few other (unrelated) RF issues which took 1-2 days each to resolve.
trobbins wrote:
Sun Aug 07, 2022 12:11 pm
I guess 25ns_1935b_1922_1602_1672_192bpi is colloquially referred to as a 1900b fill even though it seems partially loaded by 1602 and 1672 ?
Yes. There is a naming convention which for this scheme reads ...
- 1935 bunches injected per beam in total in 192 bunch trains with 25ns bunch spacing (25ns_1935b_ ... _192bpi)
- 1922 bunch pairs colliding in IP1 & 5
- 1602 bunch pairs colliding in IP2
- 1672 bunch pairs colliding in IP8

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Tau
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Re: 2022 Operation

Post by Tau » Sun Aug 07, 2022 3:04 pm

I also get the impression beam losses are a bit more than two years ago.
Is that because of the higher beta, or from the electron cloud? Our something completely different?
- Tau

M.
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Re: 2022 Operation

Post by M. » Sun Aug 07, 2022 10:47 pm

I guess you are talking about slow losses (beam lifetime), not fast/UFO losses.
There is a couple of effects that drive these. To stabilize the beams in the presence of e-cloud, we currently need strong non-linearities (chromaticity and octupoles), which are detrimental to lifetime. Also e-cloud can directly drive losses.
But once in collisions the losses are at least not much worse than in 2018, the beam lifetime is ~20-30h.

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trobbins
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Re: 2022 Operation

Post by trobbins » Sun Aug 07, 2022 11:21 pm

Thanx M. for the insight :-)

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Tau
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Re: 2022 Operation

Post by Tau » Mon Aug 08, 2022 9:57 am

M. wrote:
Sun Aug 07, 2022 10:47 pm
To stabilize the beams in the presence of e-cloud, we currently need strong non-linearities (chromaticity and octupoles), which are detrimental to lifetime. Also e-cloud can directly drive losses.
Thanks! That is exactly what I meant indeed.
- Tau

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Tau
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Re: 2022 Operation

Post by Tau » Mon Aug 08, 2022 7:19 pm

I was so excited: We just had the first 2100 bunches attempt!
I calculated there's almost 0.9 nanograms of protons in the LHC (which is already heavier than that before it arrives from the SPS, but let's ignore that detail).

And then there was another UFO. Bummer.

Let's see if the second attempt of the day is going to work.
Still excited 8-)
- Tau

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Tau
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Re: 2022 Operation

Post by Tau » Tue Aug 09, 2022 2:34 pm

Now we had an 11h hour fill. Still ended in an UFO, but I'm still happy.
As far as I know, the first fill with so many bunches (2173 bunches, of which 2160 colliding).
It is going in the right direction. :clap:
- Tau

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Re: 2022 Operation

Post by dukwon » Thu Aug 11, 2022 7:47 am

Well we had 2556b fills (with 144b trains) in Run 2. Certainly 240-bunch trains are much longer than before.

According to the Evian/Chamonix 2021 slides, the number of bunches may get up to 2748, depending on the heat load.

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trobbins
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Re: 2022 Operation

Post by trobbins » Fri Aug 12, 2022 12:23 am

The Dashboard Heat Load plot seems to show the recent step up from 192 to 240bpi, but sadly the Cryo Status plot has not recently been showing resolution of temps due to auto-scaling of one outlier.

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