Current Events Discussion

The place to discuss the LHC. Commissioning, operation, issues, events ....
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Tau
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Re: Current Events Discussion

Post by Tau » Sun Apr 25, 2010 6:51 am

LarryS wrote:Notice the second bucket in each beam does not line up (8941 vrs 8911); this will affect luminosity.
There is a deeper reason behind this; it has to do with the asymmetry of the LHCb detector.
For details, see http://blog.vixra.org/2010/04/24/lhc-ac ... zed-beams/.
Update: there's now a cool animation on that page!
Last edited by Tau on Mon Apr 26, 2010 11:59 am, edited 1 time in total.
- Tau

Kasuha
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Re: Current Events Discussion

Post by Kasuha » Sun Apr 25, 2010 6:54 am

Wow, record-breaking luminosity at record-breaking fill length, good job to LHC team!
I can see they're measuring beam parameters every now and then, I wonder if they're monitoring hump too. Such a long run could provide some new details...

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jmayes
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Re: Current Events Discussion

Post by jmayes » Sun Apr 25, 2010 1:43 pm

Looks like they made 35hrs, the longest by far!!!
:clap: :dance: :clap: :dance:

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CharmQuark
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Re: Current Events Discussion

Post by CharmQuark » Sun Apr 25, 2010 2:04 pm

Well done guys :clap: :thumbup:
Anyone who doesn't take truth seriously in small matters cannot be trusted with large ones either by Albert Einstein.

tomey36
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Re: Current Events Discussion

Post by tomey36 » Sun Apr 25, 2010 11:46 pm

what are van de mere (spelling?) scans?

oxodoes
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Re: Current Events Discussion

Post by oxodoes » Mon Apr 26, 2010 4:53 am

Van der Meer scans are a way of measuring the luminosity. Read all about luminosity and methods of measuring it at: http://cdsweb.cern.ch/record/261063/files/p117.pdf

Kasuha
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Re: Current Events Discussion

Post by Kasuha » Sun May 02, 2010 7:02 pm

Has noone noticed LHC is running physics with nominal intensity bunches?
Yay for another milestone!

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CharmQuark
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Re: Current Events Discussion

Post by CharmQuark » Sun May 02, 2010 7:08 pm

woot :thumbup:
Anyone who doesn't take truth seriously in small matters cannot be trusted with large ones either by Albert Einstein.

ali
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Re: Current Events Discussion

Post by ali » Mon May 03, 2010 11:17 am

Hi guys, another couple of questions...

So beams are now running at higher intensity (2e11) but the loss rate is much greater than with beams at 1e10. Is this how the beam is expected to behave during physics runs or something the beam commissioning is meant to prevent?
When the beam is properly squeezed would the loss rate be lower?

Also on Saturdays run there was a significant beam loss around midday, it's just visible still on the coordination page but will be off the screen soon,
from 2e11 to 1e11. Should be visible on left of the attached file. Did this cause a risk to the machine or is this something the beam scrubbers can handle easily?

Cheers, Ali
beam loss.jpg
beam loss 1 May 2010,
beam loss.jpg (49.95 KiB) Viewed 1768 times

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Tau
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Re: Current Events Discussion

Post by Tau » Mon May 03, 2010 12:47 pm

Reading through lots of documentation I get the impression that the higher intensity beams should have a better lifetime than the pilot beams. My guess is this is just a matter of adjusting the machine to the new intensity.
- Tau

Kasuha
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Re: Current Events Discussion

Post by Kasuha » Mon May 03, 2010 1:18 pm

I believe nominal intensity beams at 450 GeV are still considered safe beams. Once they accelerate them to 3.5 TeV it will be a different story.
Losses happen time to time mostly because something needs slightly different value than what it gets - I remember during squeeze comissioning they once lost about 99% of one beam at 3.5 TeV. In fact that was much bigger loss and occurred during much shorter time than what happened on Saturday.
Of course, really bad things can happen - example is the 2008 accident - but I can see they do all they can to avoid them.

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mrgumby
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Re: Current Events Discussion

Post by mrgumby » Tue May 04, 2010 7:48 am

They are gradually working up to full power. On the way to this point there WILL be glitches. We (and the ops) have to hope that the glitches are containable. That is why things are going s.l.o.w.l.y. and c.a.r.e.f.u.l.l.y.

Well done to the operators. Keep doing it just like you have been. You are wonderful! :thumbup:

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DCWhitworth
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Re: Current Events Discussion

Post by DCWhitworth » Tue May 04, 2010 9:14 am

Found an interesting fact in a CERN article recently about what the 'safe beam' tag actually does.

When the machine is operating in 'setup beam' mode they can mask various feedbacks from detectors, so if they have a slight issue with the sensitivity of something or it is slightly glitchy they can work around it by masking it so the feedback, which might cause a dump, is ignored. Obviously this is not something they want to do a lot of but is useful for working around small issues that might otherwise slow them up.

When they have unsafe beams so that the 'setup beam' flag goes out then all masks are automatically removed so everything has to be right or the MPS will kick in automatically.
DC

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CharmQuark
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Re: Current Events Discussion

Post by CharmQuark » Tue May 04, 2010 2:29 pm

Nice find DC :thumbup:
Anyone who doesn't take truth seriously in small matters cannot be trusted with large ones either by Albert Einstein.

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mrgumby
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Re: Current Events Discussion

Post by mrgumby » Wed May 05, 2010 7:55 am

this explains a lot of stuff....well done sir!

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