2012 Events Discussion

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adam_jeff
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Re: 2012 Events Discussion

Post by adam_jeff » Tue May 29, 2012 8:38 am

DCWhitworth wrote:
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.
There is indeed now a policy to avoid having bunches which collide only in IP8 as much as possible, as these showed much higher losses than other bunches. At least one dump was caused when these bunches fell below the sensitivity threshold of the position monitors, even though the other 1368 bunches were fine.
When two bunches collide, those particles which are not involved in actual collisions still receive a sideways push due to the electromagnetic field of the other beam. This 'beam-beam kick' is compensated using various corrector magnets (there is also a 'beam-beam tune shift' which is compensated by tuning the quadrupoles). The size of the beam-beam kick depends on the number of IPs each bunch collides at and the arrangement of neighbouring bunches at that IP. The isolated bunches which collide only at IP8 do not receive much kick, they are then over-compensated by the corrector magnets (which are trying to correct the average kick for all bunches) leading to a bad orbit and lots of losses.

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chriwi
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Re: 2012 Events Discussion

Post by chriwi » Tue May 29, 2012 10:51 am

thanks for that explaination adam_jeff.
bye

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bgab001
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Re: 2012 Events Discussion

Post by bgab001 » Mon Jun 04, 2012 10:16 pm

And some new records again :
fill 2692 ~240 pb-1 (2 records, max and daily max luminosity delivered) in 22.8 hours (also 2 records, best total and daily length)
Nice job! But don't forget to beat that within 2 weeks again ;-)

B.

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Re: 2012 Events Discussion

Post by Harbles » Fri Jun 08, 2012 7:55 pm

New looks for the LHC Commissioning with Beam page, http://lhc-commissioning.web.cern.ch/lhc-commissioning/
and the LHC statistics page http://lhc-statistics.web.cern.ch/LHC-S ... /index.php.

Much cleaner.

Atlas and CMS are both poised to cross through 5 fb-1 with the next fill which is pretty incredible IMHO.

Onward to the Summer Physics meetings!

Is it a bad sign when the webpage doesn't work? lol.
www.­ichep2012.­com.­au

Ah this one works.
http://indico.cern.ch/conferenceTimeTab ... 8#20120704

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DCWhitworth
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Re: 2012 Events Discussion

Post by DCWhitworth » Mon Jun 11, 2012 10:33 am

Looks like last week was good, over 1.1 fb-1 also a really alarming bug in the dump system identified and addressed.
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chriwi
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Re: 2012 Events Discussion

Post by chriwi » Mon Jun 11, 2012 1:11 pm

thanks DCWhitworth,

do you have any link to the news about the bug in the dump-system?
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DCWhitworth
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Re: 2012 Events Discussion

Post by DCWhitworth » Mon Jun 11, 2012 1:26 pm

chriwi wrote:thanks DCWhitworth,

do you have any link to the news about the bug in the dump-system?
It was in the Monday meeting presentation.

http://lhc-commissioning.web.cern.ch/lh ... -news.html

http://lhc-commissioning.web.cern.ch/lh ... mmary.pptx

It looked potentially very serious if it had ever been hit.
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terryburton
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Re: 2012 Events Discussion

Post by terryburton » Wed Jun 13, 2012 12:26 pm

For those with an interest...

The latest machine status report was presented at this morning's LHCC 110:

http://indico.cern.ch/getFile.py/access ... fId=194183

The video recording is expected to follow:

http://cdsweb.cern.ch/record/1455674?ln=en

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DCWhitworth
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Re: 2012 Events Discussion

Post by DCWhitworth » Wed Jun 13, 2012 2:36 pm

terryburton wrote:For those with an interest...

The latest machine status report was presented at this morning's LHCC 110:

http://indico.cern.ch/getFile.py/access ... fId=194183

The video recording is expected to follow:

http://cdsweb.cern.ch/record/1455674?ln=en
Thanks for the links, interesting stuff. Haven't viewed the video yet but here's some things I got from the pdf for those who want a summary ;)

'Only' 11.5 fb-1 data needed for Higgs discovery/exclusion, I thought it was 15 but that it seems was at 3.5 TeV. Estimate is actually that 13.3 will be needed to allow 15% margin for pile up etc.

They can actually put LS1 off for up to two months if needed to get more data.

Current Luminosity appears to be higher than predicted for 2012.

Integrated luminosity production appears to be on target for the 2012 estimates.

They've broken pretty much all the records this year (no surprise I suppose) most in the last two weeks.

The beam dump bug looked *really* serious - the words disaster, nightmare and armageddon appear in the presentation !
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chriwi
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Re: 2012 Events Discussion

Post by chriwi » Thu Jun 14, 2012 7:13 am

can anybody tell me why there is often the status: "waiting for injectionkickers to cool down" lately.
I cannot remeber seeing this status last year, whats new there now that they often have to wait for the kickers to cool down only recently?
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Tim Bergel
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Re: 2012 Events Discussion

Post by Tim Bergel » Thu Jun 14, 2012 12:13 pm

I've been looking at the integrated luminosity in the statistics page & there's something I don't understand. On each run the luminosity starts off pretty high and decays down so that after say 10 hours of stable beams it's about 1/3 of the initial value. I haven't tried to work out the optimal value but it seems to me as if you would get a faster rise in the integrated luminosity if you dumped after about 10 hours of stable beams & re-filled - the actual best time to do this would clearly depend upon some statistics on the probability of getting a successful refill in x hours.

But you don't seem to be doing this - instead once you have stable beams you seem to run the fill for as long as possible - and I cannot believe that you have not worked through this issue. So what is the reason for doing it this way? Is it that getting the beams stable is so tricky (& expensive?) that it's almost never worth dumping & refilling?

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chriwi
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Re: 2012 Events Discussion

Post by chriwi » Thu Jun 14, 2012 1:34 pm

to me it looks like they try to sceduel dumps somewhere around 15h or 200pB^-1 but often they dont reach this.
the only beams that were kept much longer than this were kept for the reaso nthat there was no setupbeam available from the SPS at that time so dumping would have left them with nothing, not even the chance to refill.
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Tim Bergel
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Re: 2012 Events Discussion

Post by Tim Bergel » Fri Jun 15, 2012 8:43 am

the only beams that were kept much longer than this were kept for the reason that there was no setup beam available from the SPS at that time so dumping would have left them with nothing, not even the chance to refill.
Ah - I hadn't spotted that - thanks

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DCWhitworth
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Re: 2012 Events Discussion

Post by DCWhitworth » Fri Jun 15, 2012 12:44 pm

chriwi wrote:can anybody tell me why there is often the status: "waiting for injectionkickers to cool down" lately.
I cannot remeber seeing this status last year, whats new there now that they often have to wait for the kickers to cool down only recently?
This appears to be an issue they are hitting with the higher bunch intensities. Steve Myers touched on it during his presentation above.

They've pretty much got the LHC cranked up as high as it can go right now.
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Re: 2012 Events Discussion

Post by Harbles » Sat Jun 16, 2012 10:01 pm

Let me echo Terry Burton's post about the LHC status reports. All very interesting.

2012-06-13 110th LHCC Meeting OPEN Session

LHC Machine Status report by Steve Myers (26 Min 33 Sec)
http://cdsweb.cern.ch/record/1455674

Alice Status report by Andreas Morsch (37 Min 20 Sec)
http://cdsweb.cern.ch/record/1455675?ln=en

LHCb Status report by Diego Martinez Santos (30Min 18Sec)
http://cdsweb.cern.ch/record/1455676?ln=en

ATLAS Status report by Klaus Monig (40Min 19Sec)
http://cdsweb.cern.ch/record/1455677?ln=en

CMS Status report by Yves Sirois (45Min 44Sec)
http://cdsweb.cern.ch/record/1455678?ln=en

LHCf Status report by Oscar Adriani (26Min 10Sec)
http://cdsweb.cern.ch/record/1455694?ln=en

RD51 Status report by Maksym Titov (28Min 32Sec)
http://cdsweb.cern.ch/record/1455895?ln=en

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