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Re: 2012 Events Discussion

Posted: Sat Apr 14, 2012 8:07 pm
by Tim Bergel
Everything seems to be going very smoothly ... too smoothly ...

Seriously though, is it my imagination or is it taking much less time between the end of one period of stable beams and the start of the next? The turnround only seems to take about two hours - I'm sure it used to take longer.

Re: 2012 Events Discussion

Posted: Sat Apr 14, 2012 11:23 pm
by RocketManKSC
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This is what last year looked like.

Re: 2012 Events Discussion

Posted: Sun Apr 15, 2012 6:04 pm
by morgad
2 copies of the same image? or do I need new glasses?

best regards
Dave

Re: 2012 Events Discussion

Posted: Sun Apr 15, 2012 9:40 pm
by DCWhitworth
tomey36 wrote:why is the atlas lumi so much lower than cms?
The latest USLHC blog comments on this http://www.quantumdiaries.org/2012/04/1 ... pectations they imply no one seems to know.

However the luminosity readings are only estimates I believe. They seem to have tuned the way they estimate them over the break.

Re: 2012 Events Discussion

Posted: Sun Apr 15, 2012 9:52 pm
by DCWhitworth
Tim Bergel wrote:Everything seems to be going very smoothly ... too smoothly ...

Seriously though, is it my imagination or is it taking much less time between the end of one period of stable beams and the start of the next? The turnround only seems to take about two hours - I'm sure it used to take longer.
I have to say I agree, things seem to be going seriously well. I could be mistaken but I think we've had three consecutive programmed dumps.

Re: 2012 Events Discussion

Posted: Mon Apr 16, 2012 4:50 am
by tomey36
Thanks DCWhitworth. It looks like they are about to do some VDM scans, so maybe we will know more after.

Re: 2012 Events Discussion

Posted: Mon Apr 16, 2012 3:05 pm
by adam_jeff
There have been more programmed dumps this year so far, not because the machine is better but because the priorities are different. They are trying to increase the intensity back to 1380 bunches. To get there there are a number of milestones to pass and boxes to tick, in order to satisfy the Machine Protection team that it's safe to increase the intensity. Requirements are generally something like [2 hours of Stable Beams with N bunches]. Once this is achieved they can dump and try to tick the next box. There's no point trying to keep collisions going for longer because whatever luminosity they collect now will be negligible compared to what they will get later with a full machine.

Re: 2012 Events Discussion

Posted: Tue Apr 17, 2012 9:14 am
by PhilG
@adam_jeff, your point is valid but even taking that into account the stability and turn-round times have been exceptionally good compared to last year.

The beams have been dumped at around 50% of peak lumi as they often were in 2011 if they lasted. This is quicker now because the luminosity half-life is getting shorter as luminosity increases. I wonder if they will do some longer runs to get some low pile-up data later.

Looks like they should reach the maximum 1380 bunches before the technical stop and they may even reach 1/fb. They could not have wished for more.

Re: 2012 Events Discussion

Posted: Fri Apr 20, 2012 11:22 am
by zaim
If we can trust the CMS lumi, they have delivered 1 fb^-1 in 2012 with the current fill. No doubt the LHC is running very smoothly.

Re: 2012 Events Discussion

Posted: Sat Apr 21, 2012 1:38 am
by Harbles
Atlas has a public 2012 Luminosity page.

https://twiki.cern.ch/twiki/bin/view/At ... Collisions

Re: 2012 Events Discussion

Posted: Wed May 09, 2012 9:31 am
by DCWhitworth
Tim Bergel wrote:Everything seems to be going very smoothly ... too smoothly ...

Seriously though, is it my imagination or is it taking much less time between the end of one period of stable beams and the start of the next? The turnround only seems to take about two hours - I'm sure it used to take longer.
Well since the technical stop everything seems to have gone in the opposite direction, glitches everywhere ! :?

Re: 2012 Events Discussion

Posted: Wed May 09, 2012 3:50 pm
by Harbles
Most frustrating Cryo dysfunction. They are having repeated trips of the S 78 cold compressor and are trying to hook that sector up to the S 81 compressor. They are trying to be efficient with the time though fixing and adjusting things in unaffected sectors.
I'm sure the powers that be are asking many questions about what is the fundamental problem with S 78 cold compressor reliability.

Re: 2012 Events Discussion

Posted: Sat May 12, 2012 7:39 pm
by chriwi
Looks like they have another record fill this time, ATLAS and CMS each way above 100.000 integrated fill luminoaity @ 13 houres stable beams and not yet the end.
:-)

Re: 2012 Events Discussion

Posted: Tue May 15, 2012 1:40 pm
by Harbles
Things do seem to have settled down and they are putting together back to back productive runs. Over the last four days in ten fills CMS and Atlas have each been provided with about 1/2 Fb-1 of data.
Onward!
https://lhc-statistics.web.cern.ch/LHC-Statistics/

Re: 2012 Events Discussion

Posted: Wed May 16, 2012 12:43 am
by terryburton
Onwards indeed... "During the stable beams, the injectors profited to fix the problem of emittance blow-up. The investigation was so proficuous that the SPS started re-measuring low emittances as before the TS and we decided to dump to refill."

The current fill had initial luminosities exceeding 5300 b⁻¹s⁻¹ and 5500 b⁻¹s⁻¹ for ATLAS and CMS, respectively, average of 1.38×10¹¹pb⁻¹, without losses during the ramp and squeeze.

Much admiration and respect to the teams in nearing the conclusion of a long and difficult recovery from the technical stop!