2016 operation

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tomey36
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Re: 2016 operation

Post by tomey36 » Sat Jul 09, 2016 7:08 pm

Nice link jmc. So far we haven't seen the increased lumi from the BCMS beam but I guess they are talking it slow. If they keep this pace they should get >14 FB by July 15th!

mfb
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Re: 2016 operation

Post by mfb » Sun Jul 10, 2016 6:23 pm

jmc2000 wrote:There's an interesting paper on BCMS mentioned in the link which is now being used for fills as we speak to increase the luminosity further:
http://emetral.web.cern.ch/emetral/Some ... -02-14.pdf
Note that the link is from early 2015. The current SPS limit would rule out case 1, 2 and 3, and we went to a beta* slightly below the design already.

mfb
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Re: 2016 operation

Post by mfb » Thu Jul 14, 2016 3:48 pm

Interesting news from the LPC meeting, first set of slides, in particular slide 14. Going from 96 to 144 bunches per injection can give up to 15% (ATLAS/CMS) or 20% (ALICE/LHCb) more bunch crossings - free luminosity increase without increasing pileup notably. Heat load would be worse but could be manageable. Changing some hardware interlock to better use the region close to the abort gap could give 6% (ATLAS/CMS) or 15% (ALICE/LHCb). Those two changes can be combined, for up to 22% / 38% more luminosity with up to 2532 bunches.

The BCMS is active, they will probably try to lower the emittance as soon as tomorrow, which increases the luminosity. It is unclear how much it can be increased without trouble for the LHC.

jmc2000
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Re: 2016 operation

Post by jmc2000 » Mon Jul 18, 2016 1:58 am

What's going on when there is a sudden increase in luminosity during stable beams, as shown here with Atlas at t=2:50 https://www.flickr.com/photos/48562472@ ... res/W4K8nQ

JMc

mfb
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Re: 2016 operation

Post by mfb » Mon Jul 18, 2016 5:35 am

They re-optimize the beam parameters frequently. This is partially necessary due to the ... moon.

Seriously


First BCMS beams: A new luminosity record at 110% the design luminosity, achieved two out of two times so far.

mfb
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Re: 2016 operation

Post by mfb » Mon Jul 18, 2016 1:31 pm

Some VISTARS pages got captured and put in time lapse videos - about one minute per day. Youtube channel

sciing
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Re: 2016 operation

Post by sciing » Wed Jul 20, 2016 5:42 am

CMS should just past 17/fb. Record day on monday with over 600/pb. As I had wrote 20/fb till MD1, I just realized that this should be impossible. But now still 6 days left till tuesday morning. So my my over optimistic guess it is not out of reach.
After MD1 there are still more than 10 weeks, 40/fb for the year is now really the pesimistic estimate.

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chelle
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Re: 2016 operation

Post by chelle » Wed Jul 20, 2016 10:16 pm

So the faster they go the more often they meet/collide, is that the key to a higher luminosity, or are collisions themselves becomming more *sparkling*? If it is only the former, than what is the name for generating more 'debris'? BTW how much faster are they going than two years ago, now they are at 14Tev or so and the previous at 7Tev, so what's actually the difference in velocity?
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mfb
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Re: 2016 operation

Post by mfb » Wed Jul 20, 2016 11:03 pm

The proton speed does not change. It is something like 99.999999% the speed of light - with some change in the last decimal place when we went from 4 TeV per proton (2012) to the current 6.5 (since 2015). The difference to the speed of light is about the speed of a pedestrian.

The number of protons per bunch can increase, the number of bunches can increase. The recent improvement packed the protons in a bunch closer together (where "closer" is still less dense than hydrogen gas at standard conditions).

The collisions are exactly the same as in 2015, we just get more of them per time.

Did you finally realize that you have no idea what the LHC is doing?

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chelle
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Re: 2016 operation

Post by chelle » Thu Jul 21, 2016 5:44 am

Thanks!

So 7km/h faster over a stretch of 27km.
Basically the relativistic mass of a particle increases with velocity and tends to infinity as the velocity approaches the speed of light. 



In practical terms our protons are moving a very small fraction below the speed of light. As we increase the energy (and momentum) they only get a very small fraction closer to the velocity of light – never reaching it. However, their energy and momentum do increase considerably.



For a given momentum, our magnets need to provide a force necessary to bend the beam around in the 27 km. The increase in momentum is exactly reflected in the increased force we have to apply with these magnets as we increase the energy of the beam.



http://lhc-machine-outreach.web.cern.ch ... ch-faq.htm
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chelle
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Re: 2016 operation

Post by chelle » Thu Jul 21, 2016 6:07 am

BTW regarding the numbers:
The Large Hadron Collider (LHC) is scheduled to restart for physics early in 2015 after two years of maintenance and upgrading. The collision energy at restart will be 13 TeV, a significant increase over the initial three-year LHC run, which began with a collision energy of 7 TeV, rising to 8 TeV. But the LHC was designed to run at a maximum collision energy of 14 TeV, so why has CERN decided to start the second run at a lower energy?

https://home.cern/about/engineering/res ... why-13-tev
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jmc2000
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Re: 2016 operation

Post by jmc2000 » Sun Jul 24, 2016 12:57 am

mfb wrote:The luminosity lifetime might go down a bit, but for a given time in stable beams the luminosity should always be higher, so no disadvantages (higher pileup in the experiments, but that's what you get if you want more luminosity for a given number of bunch crossings). Just challenging for the preaccelerator chain.
After trying to model the luminosity curve by the usual I = I_0*exp(-t/tau), I've found that tau varies for fill 5111 from 5 hours at the beginning to 17 hours after 6 hours. I'm hoping this means I can be modeled as:

I = I_0*exp(-t/tau1) + I_0*exp(-t/tau2) Where tau1 < tau2

Does anyone know if luminosity plots of fills over time are available online as was done in 2012?

JMc

tomey36
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Re: 2016 operation

Post by tomey36 » Sun Jul 24, 2016 4:24 pm

https://lpc.web.cern.ch/lumiplots_2016_pp.htm

Is this what you mean?
There is also the statistics page which is linked on the portal.

mfb
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Re: 2016 operation

Post by mfb » Sun Jul 24, 2016 4:45 pm

For intermediate values in fills: only from the VISTARS pages as far as I know (see a few posts above for a record of them), or with access to experiment data. There are dedicated lifetime plots from the machine operation but I don't think they are available publicly.

For (stable beam duration, integrated lumi) datapoints: Supertable


The BCMS scheme now reliably delivers 120% design luminosity.

jmc2000
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Re: 2016 operation

Post by jmc2000 » Sun Jul 24, 2016 7:11 pm

tomey36 wrote:https://lpc.web.cern.ch/lumiplots_2016_pp.htm

Is this what you mean?
There is also the statistics page which is linked on the portal.
Something more like this:
https://op-webtools.web.cern.ch/vistar/ ... p?usr=LHC3

But a luminosity plot for a particular fill rather than over the last 24 hours.

JMc

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