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*** SQUEEZE ***

Posted: Sat Oct 02, 2010 3:15 am
by amiso
Can someone explain in a few words what this consists in? It seems that this operation takes about 20 minutes!

Re: *** SQUEEZE ***

Posted: Thu Oct 07, 2010 10:50 am
by Tim Bergel
Hi Amiso,

It doesn't look like anybody else is going to have a go at explaining this so I shall have a try, but my understanding is very limited - if I get something hopelessly wrong can someone correct me. I think that, if you go to the main portal area, there is a link on the left called "Accelerators for pedestrians" which contains all sorts of information and probably a much better description of squeezing could be found.

So, first of all what happens is that a number of bunches of protons is injected into the LHC from the SPS accelerator and then they are all accelerated to 3.5 TeV inside the LHC. At this point they form a pretty even beam which I think is a few millimeters across.

Squeezing is done using the pairs of magnets on either side of a detector. The magnetic fields on both magnets is gently increased and adjusted to produce a greater focussing effect. That means that when a beam hits the first magnet it is focussed inwards, reaches its tightest point of focus at the beam crossing point - where it is rather less than a millimeter across - diverges again after the crossing point and is then re-focussed into an even beam by the second magnet on the other side of the detector. The net effect is thus to produce a much tighter, concentrated, beam exactly at the crossing point and therefore a higher level of collisions.

I think that then, as a separate operation, the beams are moved so that they intersect at the crossing point, but this adjustment may be part of the squeezing operation - I can't remember.

I hope that this makes things clearer - and that it is not grossly incorrect. Don't forget I'm just an onlooker and not someone from CERN that really understands what is going on...

Re: *** SQUEEZE ***

Posted: Sat Oct 09, 2010 9:35 pm
by Bornerdogge
I'd say that's correct 8-)

When then end the squeeze, they move to adjust mode, where they reduce the separation between the beams till collisions...

Re: *** SQUEEZE ***

Posted: Tue Nov 02, 2010 11:45 pm
by amiso
So 'squeezing' has to do with reducing the cross section only. They have no control of the length?