1.7 x10^11 PPB?

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

1.7 x10^11 PPB?

Post by jmc2000 » Thu Sep 06, 2012 8:59 pm

Fill 3034 is filling with 1.7 x10^11 PPB compared to the supposed max of 1.6x10^11 at the start of the year.

Anyone know if they're using special techniques that enable them to do this?

I was under the impression that losses at squeeze and adjust are not fully understood yet, hence the max luminosity of 7/nb/s.

Regards,

jmc.

Kasuha
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Re: 1.7 x10^11 PPB?

Post by Kasuha » Fri Sep 07, 2012 9:25 am

I always thought maximum bunch population was limited only by SPS capabilities.

andrewp
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Re: 1.7 x10^11 PPB?

Post by andrewp » Sat Sep 08, 2012 12:45 am

I pop in from time to time to see how it's all going, and of late have been a little disappointed with machine utilisation. Admittedly, some days have Physics going up to 70% of the time, but many days are like today with Physics being done less than 50% of the time. I think the theoretical limit is something like over 90%. Is there a single overarching reason for this? - like perhaps parallel activities of some sort, or equipment unreliability?

jmc2000
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Re: 1.7 x10^11 PPB?

Post by jmc2000 » Sat Sep 08, 2012 1:01 pm

andrewp wrote:I pop in from time to time to see how it's all going, and of late have been a little disappointed with machine utilisation. Admittedly, some days have Physics going up to 70% of the time, but many days are like today with Physics being done less than 50% of the time. I think the theoretical limit is something like over 90%. Is there a single overarching reason for this? - like perhaps parallel activities of some sort, or equipment unreliability?
Theoretical limit over 90%? You must be joking! :shock:

What matters is how much luminosity they're producing per week which stands at around 1/fb and this is what was hoped for at the start of the year when they were hoping to deliver 15\fb by the end of the year. If things continue as they are, they should deliver this over the remaining 2 weeks for this run slot. And there's a 10 week slot after that :D

They're cruising just fine 8-) at a peak of 7/nb/s, delivered 6.6/fb for HEP and the discovery of the Higgs, 15/fb likely to be achieved before next stop, another round of :clap: and drinks at the Cern pub.

andrewp
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Re: 1.7 x10^11 PPB?

Post by andrewp » Sat Sep 08, 2012 2:11 pm

I can see 70% by eye from "LHC Operation" over one day. You say over 90% is hilarious, but if I look at the minimum downtime between runs, it is a fact that 90%, more or less, is achievable. Why do we differ, then?

The longest runs we see are around 12 hours, with a typical intensity drop over the duration of about 25%. One hour seems to be a fairly typical idle period between runs, including ramp down/ramp up. So in 24 hours, it's easy to imagine two 11.5 hour runs plus one hour idle time, or 95.8% utilisation.

Today, for example, the utilisation has been somewhere south of 25%, by eyeball.

jmc2000
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Re: 1.7 x10^11 PPB?

Post by jmc2000 » Sat Sep 08, 2012 9:16 pm

@andrewp You could run the machine so that it's kept in stable beams for as long as possible and therefore approach 100% of time in stable beams, but it wouldn't be efficient because of the fall in intensity of the beam.

The fastest turn around between beams has been 2.25 hours, and the beam half life is around 10 hours after which it's more efficient to dump the beam and refill, giving a possible 80% in stable beams. But even this isn't theoretically realistic because of beams dumps due to all sorts of reasons such as losses, failure of a component etc. Last year 30% was approx the time spent in stable beams and this year they have improved on it, but it's no where near 80% and never will be over even a week, theoretically.

LHC time spent in stable beams for the last 48 fills is currently 37%:

https://lhc-statistics.web.cern.ch/LHC-Statistics/

which gives 9.5 hours per day and approx 1\/fb/week, which is what was theoretically predicted and hoped for last year.

andrewp
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Re: 1.7 x10^11 PPB?

Post by andrewp » Sat Sep 08, 2012 9:56 pm

Yeah, OK, I guess that's the way it is. The Statistics plot looks reasonably straight line slope, so I guess we'll make or exceed target. Just today there have been about three failures. All credit to the crews though; they seem to jump on them immediately to work and fix the problems.

Thanks for the input!

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