Large Hadron Collider Test

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Kasbah said:
I may be way off here but I think that "production collisions" is a term used for quarks that are produced due to the colliding of the hadrons, protons and neutrons. This in turn will allow an advancement in the experimental program currently in progress at the Relativistic Heavy Ion Collider (RHIC). The aim of the heavy-ion program is to provide a window on a state of matter known as Quark-gluon plasma, which characterized the early stage of the life of the Universe.
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Well, "production collisions" just means the collisions that happen at the highest energy of the accelerator - these are the collisions that we hope will produce the exciting things (Higgs, supersymmetry) that we're all looking for.

The LHC uses protons only to collide (we use magnets to bend the particles around the track, which is why we can't do it for neutrons). The protons are accelerated in 3 smaller accelerators, then injected into the LHC at 450 GeV.

When they first start running (again) they will probably do some "low energy" collisions - 450 GeV with 450 Gev to make a combined center-of-mass energy of 900 GeV. Then they'll ramp up the LHC magnets, accelerate the protons to maybe 5 TeV each, and then do the "production" or "high energy" collisions.

On RHIC - RHIC collides heavy ions (lead, I think) to make the QGP. The LHC will also have lead ion collisions, but probably not until next year.
 
remybfg10k said:
Next year June yup,

Although i'm betting everything on them doing the first "production" collision on December 21st 2012

:D
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Thats marked for June THIS YEAR. That article was posted last year December.

Kalvaer.. End of Nov you say? :)
Cant wait! Looking forward to this...
 
claire.lee said:
The LHC uses protons only to collide (we use magnets to bend the particles around the track, which is why we can't do it for neutrons).
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What I am wondering is this, are these magnets set up to a certain strength before the experiments or do they get adjusted as the proton flies around? As I see it, the first would require amazingly accurate calculations and performance to the specification of the experiment, the second would pose a challenge in how to adjust a magnetic field quickly enough when the controlled proton is close to the speed of light, how do the controls keep up with the proton?
 
risingtide said:
What I am wondering is this, are these magnets set up to a certain strength before the experiments or do they get adjusted as the proton flies around? As I see it, the first would require amazingly accurate calculations and performance to the specification of the experiment, the second would pose a challenge in how to adjust a magnetic field quickly enough when the controlled proton is close to the speed of light, how do the controls keep up with the proton?
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I'm sure Claire will be able to explain in more detail (she has an early lecture to give this morning) but the magnetic field is adjustable and there are more than just one type of magnet. If conventional magnets were used, the LHC would be 120 km's long :eek:

Firstly the protons are brought up to speed in smaller accelerators which are easier to control and then allowed to leave in bursts along the LHC.

Once inside, the magnetic dipoles magnets (14,3 m long and weigh around 35 tons) bend the beam around the LHC. There are also quadrupole magnets that focus the beam. Then sextupole magnets (which I think are more correcting magnets that take other factures into account and finally inner triple magnets that focus the beams for collision.

The calculations though, can be found on the cern website and are controlled and monitored by some of the biggest server banks of computers ever built. The amount of fibre optics in this system I am sure will pretty much beat Telkoms infrastructure in SA :D Almost all of it is for monitoring hardware.

Things can go wrong though and if it is found that the beam is going to far of course for them to correct, the whole beam can be dumped. I cant remember the exact figures, but it happens so quickly that by the time a dump warning is displayed on the control room screens, the entire LHC should be beam free already. IF the beam cant be dumped in time, it could punch a hole straight through the accelerator, and pretty much anything in its path.
 
Kalvaer's exactly right :)

The protons get injected into the LHC at 450 GeV. Then, the LHC team will increase the protons' energies to up to 7 TeV with the use of RF cavities, and while increasing the power of the magnets to keep them bending round the track. After they've got to 7 TeV, they will run for about 12 hours or something with that "set" of protons, before dumping them and injecting new ones.

For more details of how it all works check out the CERN fun facts guide (pdf):
http://physics.uj.ac.za/wiki/psi/ATLAS/AtlasLinks?action=download&upname=cernfunfacts.pdf

And for fun, you can check out here for everything you've ever wanted to know about the LHC and more...
http://physics.uj.ac.za/wiki/psi/ATLAS/AtlasLinks
 
More great news... NOT..

Not really sure if I am allowed to post this here but I am going to.

News on the LHC

The foreseen shutdown work on the LHC is proceeding well, including the powering tests with the new quench protection system. However, during the past week vacuum leaks have been found in two "cold" sectors of the LHC. The leaks were found in sectors 8-1 and 2-3 while they were being prepared for the electrical tests on the copper stabilizers at around 80 K. In both cases the leak is at one end of the sector, where the electrical feedbox, DFBA, joins Q7, the final magnet in the sector.

Unfortunately, the repair necessitates a partial warm-up of both sectors. This involves the end sub-sector being warmed to room temperature, while the adjacent sub-sector "floats” in temperature and the remainder of the sector is kept at 80 K. As the leak is from the helium circuit to the insulating vacuum, the repair work will have no impact on the vacuum in the beam pipe. However the intervention will have an impact on the schedule for the restart. It is now foreseen that the LHC will be closed up and ready for beam injection by mid-November.
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Devill said:
O we know that :mad: :p
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Kalvaer said:
More great news... NOT..

Not really sure if I am allowed to post this here but I am going to.
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Like I said:(

think maybe I should just forget about it for a while...

FFS I want this to be done NOW! :mad:

Wonder if it will be up and going before 2012... and then we still have to wait a long time for the data to be spiffed and polished

//cries
 
Kalvaer said:
Once inside, the magnetic dipoles magnets (14,3 m long and weigh around 35 tons) bend the beam around the LHC. There are also quadrupole magnets that focus the beam. Then sextupole magnets (which I think are more correcting magnets that take other factures into account and finally inner triple magnets that focus the beams for collision.
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Dipoles, are as you say, bending magnets, quads do two things, focus in one dimension on the plane perpendicular to the beam direction (i.e. x or y if the beam is the z, actually the beam direction is referred to as the s. Please don't ask me why). You cannot focus on both axes on that plane similtaneously because it would violate maxwell. Quads also centre the beam. If the quad is either long enough or the field strength is sufficient. Sextupoles correct for chromatic aberation. When the beam passes through eithe dipoles of quads the higher energy particles become separated from the lower energy particles (the energy spread or dE). Sextupoles correct for this.

Combine two quads, one focussing in the x plane and the other in the y plane and you have something called strong focussing or alternating gradient.
 
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risingtide said:
What I am wondering is this, are these magnets set up to a certain strength before the experiments or do they get adjusted as the proton flies around? As I see it, the first would require amazingly accurate calculations and performance to the specification of the experiment, the second would pose a challenge in how to adjust a magnetic field quickly enough when the controlled proton is close to the speed of light, how do the controls keep up with the proton?
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RisingTide: they don't. The beam behaves a bit like a long piece of hosepipe, a bit flexible but not "floppy". It does go where you want it to, sometimes it's difficult sometimes it's easy but you don't have particles flying around all higgeldy piggeldy. The magnets we are dealing with usually have very high inductances (in the LHC dipoles case probably in the order of 10's of henrys) so they have a correspondingly high time delay or tor and do not react to very fast events.

Can a particle beam and it's steering magnets be modelled by control theory? Don't know.

To answer your question: yes the magnets are set to predetermined values before beam is injected, the system cannot react quickly enough to indivudual partcles to control them in real-time. But the beam is a fairly slowly changing phenomena and the magnets are adjusted for the beam in real-time.
 
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Kalvaer said:
Things can go wrong though and if it is found that the beam is going to far of course for them to correct, the whole beam can be dumped. I cant remember the exact figures, but it happens so quickly that by the time a dump warning is displayed on the control room screens, the entire LHC should be beam free already. IF the beam cant be dumped in time, it could punch a hole straight through the accelerator, and pretty much anything in its path.
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The beam will, generally, be dumped where it hits the beam pipe. The power in a beam (there are two, contrarotating beams) is mind-boggling. 7TeV x 0.5Amps (yup that's right folks, normally we work in nanoamps or at my present facility 0.5 milliamps) so you're looking at 3.5 TWatt!!!! BUT it's a pulsed beam so that's the peak power.

Now you're probably thinking that that power will dissapate in the walls of the beam tube. It doesn't. Protons exhibit something called a Bragg peak where the majority (i.e. 90%) of the energy is dumped at the end of its path, at that energy the end of that path is probably somewhere MILES (feel free to do the math, use the Bethe equation. It gives me the heebs. Alternatively you can use GEANT4, something with which Claire will be very familiar) away (after travelling through rock) and not in the beam line proper.

In otherwords, once it's hit the beam line it's too late anyway.
 
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Kalvaer said:
but the magnetic field is adjustable and there are more than just one type of magnet. If conventional magnets were used, the LHC would be 120 km's
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The rule of thumb is: Energy (GeV) = 0.3 x Field Strength x Radius (m).

So considering the LHC, circumference is 27km, giving us a radius of 4,300 m. Energy is 7TeV or 7000 GeV. So simple maths yields a required field strength of
5.46 Tesla. Not possible with an iron based magnet which will saturate at (approx) 2.5T. Plug this into the equation and we get: 58.6km circumference.

Using Kalvears number (circumference = 120Km) we find that the field strength required will be 1.221T. Considering the pole gap required this field strength is perfectly feasible and so too would be the radius.

This is the major limitation with high energy machines today. Read up on NED (next european dipole) for a suggested solution.
 
TooFastTim said:
In otherwords, once it's hit the beam line it's too late anyway.
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I cant find the paper now, but I remember reading that normally lead was used at the end of the beam dump sites. However due to the power of the LHC, the dump sites would have to be incredible long, and the heat generated would melt everything into a solid block which would take months to repair. I cant remember what the composition is exactly now (something like carbon/kevlar/lead blocks). Even with the LHC being underground through, a stray beam would break the surface wouldn't it if it couldn't be dumped?

Oh and another thing that interesting, Part of the reason why the LHC was built underground was not safety, it was for cost. Building underground allowed them to get away with certain land rights and thus make it cheaper :D

There was also another article where a beam did go off course. I think it was at the tevatron and the punched holes through thier magnets, Do you know which one it was? I've asked Claire but she cant seem to remember :confused:
 
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