2012 Events Discussion

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Longshot
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Re: 2012 Events Discussion

Post by Longshot » Sat May 19, 2012 3:04 am

Beams just dumped on a 170 pb^-1 fill! Is this a record for the LHC so far?

Now filling with a new scheme. Still 1380b, but few more expected bunch pairs at IP 1 and 5, (CMS/ATLAS) and a few less at point 8 (LHCb). Anyone know why the change?

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Tim Bergel
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Re: 2012 Events Discussion

Post by Tim Bergel » Sat May 19, 2012 9:02 am

Can anybody explain to me what causes the short downward blips every 100 mins or so in the luminosity trace during stable beams? At first I thought they were glitches but they seem too regular to be unintentional.

Fingers crossed but things seem to be running smoothly again. Impressive work.

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DCWhitworth
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Re: 2012 Events Discussion

Post by DCWhitworth » Sat May 19, 2012 9:17 am

Tim Bergel wrote:Can anybody explain to me what causes the short downward blips every 100 mins or so in the luminosity trace during stable beams? At first I thought they were glitches but they seem too regular to be unintentional.

Fingers crossed but things seem to be running smoothly again. Impressive work.
If it's LHCb it will be the luminosity levelling working. Otherwise it's possibly something similar with the beam alignment being tuned slightly.
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DCWhitworth
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Re: 2012 Events Discussion

Post by DCWhitworth » Sat May 19, 2012 9:23 am

Longshot wrote:Beams just dumped on a 170 pb^-1 fill! Is this a record for the LHC so far?

Now filling with a new scheme. Still 1380b, but few more expected bunch pairs at IP 1 and 5, (CMS/ATLAS) and a few less at point 8 (LHCb). Anyone know why the change?
Yes a new record as announced here - https://twitter.com/#!/CMSexperiment

Not quite sure why the new scheme but IP1 and 5 are CMS and ATLAS so they'll take all the collisions they can get. The thought appears to be to avoid IP8 only collisions (i.e. bunches that only collide in IP8), not sure why need to read a few more reports.
DC

The LHC - One ring to rule them all !

RocketManKSC
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Re: 2012 Events Discussion

Post by RocketManKSC » Sat May 19, 2012 6:59 pm

Check the LHCb log and those chnages luminosity seem to line up with LHCadjusting the Beam.

Harbles
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Re: 2012 Events Discussion

Post by Harbles » Sun May 20, 2012 2:46 am

They seem to have broken their record of yesterday already. Fill 2646 passing through 180 and approaching 200 fb-1.
https://lhc-statistics.web.cern.ch/LHC-Statistics/

*Edit
And indeed Fill 2646 is another record.
16 hours 6 minutes of stable beams 187.8 pb-1 delivered to ATLAS 194 pb-1 delivered to CMS.
With 2 fb-1 in the bank already this year they have to do that forty more times and they will have the 10 fb-1 they targeted for. (Fifty more times if the target was 12 fb-1 I forget now)

Celladoor
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Re: 2012 Events Discussion

Post by Celladoor » Mon May 21, 2012 8:09 pm

- 21.05.2012 Cryo dysfunction
- 20.05.2012 Cryo dysfunction
- 16.05.2012 Cryo dysfunction
- 13.05.2012 Cryo dysfunction
- 11.05.2012 Cryo dysfunction
- 09.05.2012 Cryo dysfunction
- 08.05.2012 Cryo dysfunction
- 05.05.2012 Cryo dysfunction
- 04.05.2012 Cryo dysfunction
- 03.05.2012 Cryo dysfunction
- 01.05.2012 Cryo dysfunction

and many other problems....

What's going on?
:think:

pcatom
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Re: 2012 Events Discussion

Post by pcatom » Tue May 22, 2012 7:30 pm

Can anybody explain to me what causes the short downward blips every 100 mins or so in the luminosity trace during stable beams? At first I thought they were glitches but they seem too regular to be unintentional.

Fingers crossed but things seem to be running smoothly again. Impressive work.
Every now and again there is a luminosity scan to make sure that the beams are fully in collision this produces the blips

Harbles
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Re: 2012 Events Discussion

Post by Harbles » Wed May 23, 2012 2:33 am

And another record fill 2651 over 200 pb-1 delivered to both CMS and ATLAS.
Good show!

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chriwi
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Re: 2012 Events Discussion

Post by chriwi » Wed May 23, 2012 3:27 am

yes, Atlas ended up with 209pb-1 after ca. 20h of run. :-)
bye

chriwi

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Tim Bergel
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Re: 2012 Events Discussion

Post by Tim Bergel » Wed May 23, 2012 9:47 pm

Thank you everyone for coming up with answers to my question. Much appreciated.

Harbles
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Re: 2012 Events Discussion

Post by Harbles » Thu May 24, 2012 4:30 pm

A question for those in the know at the LHC, will they consider limiting the length of fills?

An un-scientific possibly anecdotal observation notes that the record fill of about 20 hours( fill 6551) produced on average 10.7 pb-1 / hour of integrated luminosity whereas shorter fills ( fill 6557 ) produced on average 15.3 pb-1 / hour of integrated luminosity. Assuming they are able to refill, squeeze and adjust in under two hours wouldn't shorter runs ( 6 - 8 hours ) be more efficient?

Thanks.

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chriwi
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Re: 2012 Events Discussion

Post by chriwi » Thu May 24, 2012 4:42 pm

Seems reasonable what you say, but to me it rather also applies here: never touch a running system, average turnaroundtimes of 2h look like nothing more than a nice wish to me. Observing rather shows that problemtimes of 5 to 10h after every 2nd dump seem to be the more likely case atm.
bye

chriwi

Kasuha
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Re: 2012 Events Discussion

Post by Kasuha » Fri May 25, 2012 5:36 am

They do optimize for this, except they don't expect the shortest posible turnaround time but an average one.

Harbles
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Re: 2012 Events Discussion

Post by Harbles » Sun May 27, 2012 3:30 pm

Pesky cold compressor in P8 giving problems. AGAIN! I bet there were thunderstorms in the Geneva area Friday night / Saturday morning as the power perturbations they cause seem to give the Cryo system in particular big problems.

I realize a battery based UPS would be prohibitively expensive to protect the Cryo system (and PCs and crates) from disruptions caused by lightning hits on the hundreds of Kilometres of power lines feeding the CERN complex but I wonder if they have done any studies on flywheel based UPS capable of smoothing out lightning caused perturbations that usually only last a second or two. I envision a number of smaller units (rather than one very large one) distributed around the ring and located close to the loads.

With the economic situation in Europe looking the way it does I suppose it's enough to hope to maintain the status quo let alone any capital expenditure on improvements.

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