# Particle Accelerators and Angular momentum (Crazy question)

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1. Mar 21, 2012

### dkotschessaa

Prompted by my visit to Fermilab last week...

I'm sure somebody has thought of this, but I'd be interested on hearing what the challenges would be. So, in order for us to accelerate particles to higher and higher speeds, we are needing larger accelerators. But what if, in order to get around this challenge, we build a synchotron which mechanically contracts itself into a smaller circle once the particles have started, thus conserving angular momentum and causing the particle to go faster?

2. Mar 22, 2012

### M Quack

It is not getting the particles to the necessary speed that is the problem, it is the loss of energy due to radiation each time the particles go through a bending magnet to keep them on a (roughly) circular orbit.

For this reason high energy accelerators become bigger and bigger, to make the radius of curvature bigger and thus the centripetal acceleration smaller.

There even are a few designs to build linear colliders to avoid these losses - the ill-fated SSC, and the Stanford Linear Collider.

http://en.wikipedia.org/wiki/SLAC_National_Accelerator_Laboratory#Stanford_Linear_Collider

This Wiki entry has a nice section on circular and linear colliders:

http://en.wikipedia.org/wiki/International_Linear_Collider

Last edited: Mar 22, 2012
3. Mar 22, 2012

### dkotschessaa

I see... We visited argonne as well, and I believe this is the "annoying radiation" that they actually utilize in the work that they do.

I see.

Thank you.

-Dave K

http://en.wikipedia.org/wiki/International_Linear_Collider[/QUOTE]

4. Mar 22, 2012

Staff Emeritus
That only matters for electrons. For proton accelerators, synchrotron radiation is irrelevant when it comes to the maximum energy.

When you shrink your synchrotron, what keeps the protons in their orbit? Remember, the beam is in vacuum, not scraping against the walls.

5. Mar 22, 2012

### dkotschessaa

By "that" you mean the loss of energy that M Quack was talking about?

Well I was thinking that there could be some way of designing a magnet that could pull itself inward while the beam is zipping around and the whole thing is shrinking.

I realize that if it was feasible somebody would have done it by now.

-DaveK

6. Mar 22, 2012

Staff Emeritus
When you shrink the magnet, the field has to go up, right? So why not build a stronger magnet to begin with?

7. Mar 22, 2012

### ZapperZ

Staff Emeritus
If you visited the APS, they don't actually use those "annoying radiation". Instead, what they tend to use is the radiation generated when the electron bunches passed through various insertion devices, such as undulators and wigglers.

Zz.

8. Mar 22, 2012

### M Quack

...which are nothing else than extra magnets to create even more "annoying radiation". The resulting x-rays can burn holes through steel (the x-rays, not the electron beam).

Synchrotron light sources now vastly outnumber high energy machines.

http://www.lightsources.org/cms/