intensity not dropping in 12 hours

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Xymox
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intensity not dropping in 12 hours

Post by Xymox » Mon Apr 05, 2010 6:45 am

There have been 12 hours of constant collisions.. This should deplete the beam of protons, yet intensity is exactly the same as when they declared stable beams...

Im confuzed...

Shouldn't collisions deplete the beam and drop intensity ?

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Re: intensity not dropping in 12 hours

Post by rcl » Mon Apr 05, 2010 8:20 am

It has gone down very slightly... IIRC, the beam lifetime at nominal is meant to be about a day, and at present the collision rate is about a millionth of nominal, so I would expect the depletion to be very small at the moment.

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Re: intensity not dropping in 12 hours

Post by serych » Mon Apr 05, 2010 9:06 am

rcl wrote: at present the collision rate is about a millionth of nominal, so I would expect the depletion to be very small at the moment.
It's not question of the present collision rate. Now the luminosity is about 2e+10 protons in bunches and the collision rate is approximately form 11 to 45 per second. in the nominal beam the luminosity will be about 1e+13 protons and also the collision rate shall increase 2 to 3 orders.
Lifetime of the beam is not determined so much by the depletion of particles but mainly by the decreasing quality of the bunches (they are warming up by the collisions, which means that the particles are not so nicely concentrated inside the small bunches, bunches are lenghtening and spreading across) in other words the beam is defocusing. This causes, that the probability of the collisions is decreasing, so at some moment it is better for physicists to cycle and refill the machine.
The lifetime for B1 and B2 from a while ago log information (after more than 16 hours of physics) is about 990 respectively 730 hours in transversal plane and 200 respectively 250 hours in longitudinal axis.

Fantastic!!!! :dance:

Let the protons colide!

Jakub

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Re: intensity not dropping in 12 hours

Post by Xymox » Mon Apr 05, 2010 10:41 am

Nice answer !... With color !...

From PCAtom
Hi Chris,

Only a very small fraction of the beam is burned up by the collisions – this will be different when we are at nominal intensity.

If we have a an event rate of 100Hz (actually it is more like 50Hz) we would collide 360,000 protons per hour – in a 20hour fill this would be 7.2 million protons per beam. Since we have over 2x10+10 protons in each beam this represents 3.6x10-4 of the beam – you won’t notice it!

At nominal intensity and luminosity we would expect around 40% of the beam to be lost due to collisions during a fill.

We will probably go for 24 hours - or close to it – for the fill today. Just so we can say we did it!

Cheers Paul.

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Re: intensity not dropping in 12 hours

Post by Xymox » Mon Apr 05, 2010 10:56 am

I then asked another question

"Where can we see what the actual raw collision rate is ? not the accepted rates. L0 is accepted right ?"
The experiments have not got their act together with giving us a consistent set of numbers yet. They are working on it.

Atlas and CMS seem to be giving luminosity in units of 10+30. This they are presently running around 0.9x10+27.

If I remember rightly 36Hz will give a luminosity of 10+27 – but I might be wrong ... Have to look it up!

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Re: intensity not dropping in 12 hours

Post by serych » Mon Apr 05, 2010 11:46 am

There we are - 13:30 beam lost due to momentary "lost cryo mantain in 78". :cry:

Not 24 yet, but 21 hours of stable beem on 3,5 TeV is great result!!! :clap:

Jakub

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Re: intensity not dropping in 12 hours

Post by Chuli » Mon Apr 05, 2010 7:12 pm

Can someone explain to me why the intensity was so low with the collisions? I figure it was planned, but would like to confirm it :)
Would also appreciate it if someone has a timeplan of increasing intensity :)

Tnx

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Re: intensity not dropping in 12 hours

Post by Kasuha » Mon Apr 05, 2010 7:28 pm

Intensity looks normal to me. They're still using 'safe beams' that wouldn't destroy things badly if something goes wrong. They will sure increase both intensity and number of bunches in beams but exact schedule isn't known to me.

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Re: intensity not dropping in 12 hours

Post by Danny252 » Mon Apr 05, 2010 10:39 pm

Chuli wrote:Can someone explain to me why the intensity was so low with the collisions? I figure it was planned, but would like to confirm it :)
Would also appreciate it if someone has a timeplan of increasing intensity :)

Tnx
They were using only 2 bunches per beam - versus the [quite a few more] bunches they plan to have in a full fill - upper limit for bunches is 2808, IIRC?

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Re: intensity not dropping in 12 hours

Post by Xymox » Tue Apr 06, 2010 7:56 am

Luminosity...

We all love luminosity...

16 bunches per beam would be fun... Im sure they will get there soon enough...

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Re: intensity not dropping in 12 hours

Post by DCWhitworth » Thu Apr 08, 2010 8:22 am

Xymox wrote:Luminosity...

We all love luminosity...

16 bunches per beam would be fun... Im sure they will get there soon enough...
According to this http://lhc-commissioning.web.cern.ch/lhc-commissioning/ increasing intensity is next after squeeze commissioning (which they are currently doing). Aim is to get 43 bunches !
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Re: intensity not dropping in 12 hours

Post by DCWhitworth » Thu Apr 08, 2010 8:28 am

Interesting to notice LHCb Page 1 has been updated. The estimated beam lifetime displays used to peak at 100 hours now they seem to go up to 999 which means some impressive beam lifetimes are being shown.
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Re: intensity not dropping in 12 hours

Post by Xymox » Sat Apr 10, 2010 9:23 am

Injection test today that went to 7E10 per bunch... Impressive if they do that with 43 bunches !

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Re: intensity not dropping in 12 hours

Post by DCWhitworth » Sat Apr 10, 2010 2:57 pm

Xymox wrote:Injection test today that went to 7E10 per bunch... Impressive if they do that with 43 bunches !
They actually had 1e11 in for a while last night, they did a 1.1e11 injection but it decayed pretty rapidly, something to do with RF not being configured to work above 1e11 yet.
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