2017 Operation

The place to discuss the LHC. Commissioning, operation, issues, events ....
mfb
Posts: 168
Joined: Sat Oct 03, 2015 7:58 pm

Re: 2017 Operation

Post by mfb » Mon Jul 31, 2017 8:24 am

10/fb for both ATLAS and CMS. Data-taking makes nice progress, more than 0.6/fb in the last 24 hours.

mfb
Posts: 168
Joined: Sat Oct 03, 2015 7:58 pm

Re: 2017 Operation

Post by mfb » Thu Aug 03, 2017 9:12 pm

Based on the recent MD block, the machine operators are confident that they can go to beta* = 30 cm later (down from 40 cm).

jmc2000
Posts: 146
Joined: Sun May 08, 2011 2:51 pm

Re: 2017 Operation

Post by jmc2000 » Sun Aug 06, 2017 1:05 am

Atlas currently recording o.5\fb every 13 hours giving >3.5\fb per week for 55% beam time

JMc

mfb
Posts: 168
Joined: Sat Oct 03, 2015 7:58 pm

Re: 2017 Operation

Post by mfb » Sun Aug 06, 2017 2:21 am

14 hours into the current run, 520/pb.

15.5 weeks of data-taking remaining. If the LHC keeps running as in the last few days, we get 3.5/fb per week and 55/fb more, for a total of more than 60/fb. That is probably too optimistic, but 50/fb doesn't look unrealistic.

jlourenc
Posts: 9
Joined: Wed Apr 27, 2011 4:52 am

Re: 2017 Operation

Post by jlourenc » Fri Aug 11, 2017 3:40 pm

Hi
Can anyone share information about why they’re back to scrubbing (without getting in trouble)?
I haven’t seen any UFO reports.
Thanks
Joao

jmc2000
Posts: 146
Joined: Sun May 08, 2011 2:51 pm

Re: 2017 Operation

Post by jmc2000 » Fri Aug 11, 2017 5:01 pm

They were trying for increased bunch intensity, but lost the beam several times upon ramping; so I guess the scrubbing is to "clean" the beam path in the hope this will improve things.

JMc

jlourenc
Posts: 9
Joined: Wed Apr 27, 2011 4:52 am

Re: 2017 Operation

Post by jlourenc » Fri Aug 11, 2017 5:58 pm

Thanks JMc ... keep my fingers crossed so that they reach the 40 ;)
More difficult to understand what’s going on without access to the daily meetings
Best
Joao

jmc2000
Posts: 146
Joined: Sun May 08, 2011 2:51 pm

Re: 2017 Operation

Post by jmc2000 » Tue Aug 15, 2017 2:33 pm

Does anyone know why, for the past week, they're having to slowly ramp up the intensity again?

Jmc

mfb
Posts: 168
Joined: Sat Oct 03, 2015 7:58 pm

Re: 2017 Operation

Post by mfb » Tue Aug 15, 2017 2:44 pm

They still seem to have problems with beam losses, same point as before.

1.10E11 protons/bunch currently.

Edit Wednesday: Bunch number is oscillating a bit depending on dump reasons, but now we have a stable run with 1550 bunches.

jmc2000
Posts: 146
Joined: Sun May 08, 2011 2:51 pm

Re: 2017 Operation

Post by jmc2000 » Wed Aug 16, 2017 5:21 pm

They've moved from 144bpi to 96bpi which looks interesting... perhaps the lower bpi are more efficient in scrubbing the injectors and minimizing loses?

JMc

mfb
Posts: 168
Joined: Sat Oct 03, 2015 7:58 pm

Re: 2017 Operation

Post by mfb » Thu Aug 17, 2017 8:53 am

They tried 1940 bunches overnight, dumped again from losses. 1740 worked for a while but then got dumped due to losses as well.

They switched to 96bpi with fill 6072, the night to Saturday, after the scrubbing. It should reduce the heat load, but you can't get 2556 bunches that way.

They tried to fill with 1.25E11 p/bunch before the problems started. That would have been a big step in luminosity.

mfb
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Re: 2017 Operation

Post by mfb » Tue Aug 22, 2017 9:00 am

Data collection slowed down notably. We still get above 30/fb this year with the current speed, but it is certainly not optimal. Let's hope they solve that issue.

jlourenc
Posts: 9
Joined: Wed Apr 27, 2011 4:52 am

Re: 2017 Operation

Post by jlourenc » Sat Aug 26, 2017 7:46 am

Hi
Can anyone post a summary of the problems the lhc team is currently facing?
My understanding is 16L2 is giving them a headache (conditioning problem? Is this the ‘replaced’ magnet over eyets?) Thanks a lot (yeah, I really miss those daily meeting minutes)
Joao

mfb
Posts: 168
Joined: Sat Oct 03, 2015 7:58 pm

Re: 2017 Operation

Post by mfb » Sat Aug 26, 2017 12:56 pm

They reduced the meetings to Monday/Wednesday/Friday (with an additional meeting tomorrow).

16L2 is the problem, dumping most of the fills, typically during the ramp or quickly after. Some of the dumps are from beam 1, some from beam 2, which is quite strange.
Actually, the dump signal does not come from 16L2. The typical signature is an increase in losses there, then a few milliseconds later (a few tens of revolutions) there are big losses in IR7 leading to a beam dump. 16L2 is between ATLAS and ALICE, IR7 would be a possible detector place halfway between ATLAS and CMS at the side where LHCb is.

Warming up the affected region released much more gas than expected. It reduced the normal losses as expected, but made the anomalous peak losses even worse.

Going to shorter bunch trains was simply an experiment that seemed to work initially, but with the current failure rate I'm not sure about that.

The leading hypothesis now seems to be gas-related, triggered by the electron cloud or changed thermal conditions during a run. It would be possible to warm up the whole sector and cool it again, but that would take the largest part of the time reserved for data-taking. It might be done over the end of the year stop. For now the idea is to try different filling schemes to reduce the risk, while investigating how the gas could be removed without warming up the whole sector.


Edit: Stable beams with 1164 bunches on Saturday, 70% design luminosity initially. I hope that will get better.

jlourenc
Posts: 9
Joined: Wed Apr 27, 2011 4:52 am

Re: 2017 Operation

Post by jlourenc » Sun Aug 27, 2017 12:42 pm

Thanks for the update mfb!

I assume getting rid of the gas would need more than just getting those ion pumps running.
From the look of it they switched to "make the most of now" mode and are back to producing luminosity even if at a relatively low number of bunches. Maybe we will some more experiments to get rid of the problem during the next TS or machine development slots.
Best
Joao

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