# LHC why so large?

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1. Aug 14, 2012

### sirchick

LHC why so large??

Hey

I was wondering why the size of these particle smashers is important ? When they mention they send the particles around many times per second... why did it require such large size?

Could they not build it smaller and just make it travel many more times in the circle to achieve the same distance ??

Is the distance the primary issue here or is it the fact that its not uniform motion (like a straight line) .. ?

I've not ever seen many scientists who talk about the machine explain in videos why they have to be larger in size =/

2. Aug 14, 2012

### Drakkith

Staff Emeritus
Re: LHC why so large??

The particles they are smashing together need to be at extremely high speeds. One of the things that happens with charged particles is that they emit EM radiation and slow down when they are accelerated. This includes the acceleration that we must do on them to keep them in a circular path. They LHC is so large because the turing radius has to be large enough to keep the particles from emitting so much EM radiation that we can't accelerate them to a high enough speed.

3. Aug 14, 2012

### Jimmy

Re: LHC why so large??

When charged particles accelerate, they radiate energy- this includes the radial acceleration as the particle moves around in a circle. With a larger circle, you have less radial acceleration- and less energy is radiated away.

4. Aug 14, 2012

### sirchick

Re: LHC why so large??

So would a straight line technically be more beneficial and easier to keep them at higher speeds?

Plenty of room in a desert in USA for example.

5. Aug 14, 2012

### Drakkith

Staff Emeritus
Re: LHC why so large??

Yes, but the problem is that it takes time to get the particles up to speed and a linear accelerator long enough to do so would be much larger than the LHC.

6. Aug 14, 2012

### sirchick

Re: LHC why so large??

Ah i see - So is the LHC most likely the largest we will ever need or is it likely they want to build a bigger one ?

Do we have predictions to make that the LHC cannot answer due to not high enough energies?

7. Aug 14, 2012

### ZapperZ

Staff Emeritus
Re: LHC why so large??

The history of high energy physics accelerator is that it is typically hardron-electron-hadron-electron-hadron collider. It means that often, after a discovery is made using either proton-proton or proton-antiproton, the next one being built is usually a lepton collider (ie. e-e or e-p).

So if we follow that pattern, the next logical accelerator will probably be an electron or lepton accelerator. There was the International Linear Collider that had been planned (~10 to 20 km long), but that seems to be losing support and on its last breath. There are now plans being discussed by many different groups of a "Higgs factory", but whether this is going to be a LEP type or linear accelerator such as the one at SLAC remains to be seen.

Zz.

8. Aug 14, 2012

### sirchick

Re: LHC why so large??

Can they not do the same at LHC by just sending different particles instead of building an entire new machine ?

9. Aug 14, 2012

### Nabeshin

Re: LHC why so large??

Is this really the limiting factor? I was under the impression it was the fact that you need tremendous B-fields to bend the particles into a circular path to begin with. The smaller the path, the more intense the B-field necessary, so the limiting element is how strong your magnets are for whatever energy you want to accelerate your particles to.

10. Aug 14, 2012

### Staff: Mentor

Re: LHC why so large??

You are right, the dipole magnets are the limit for hadron colliders.
Their design value is 8.3 Tesla, to achieve this in thousands of superconducting magnets is not easy. There are plans to increase this by a factor of ~2, but the technical limit on magnets is not far away.
Synchrotron radiation is about 3keV per turn and proton - while it has to be taken into account to keep the beam in the ring, it is completely negligible compared to the acceleration capacity.

Synchrotron radiation limits the energy in electron/positron colliders like the LEP. The next electron/positron machine is planned as linear accelerator, as a ring with the planned energy would be too large.

There are many predictions for even higher energies, but most of them are impossible to test with current technology (they would require an accelerator around the whole equator or even bigger machines) - and the others can be tested with the LHC.

They used the same ring for LEP (electron-positron collider) before.