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Do protons in the beam on LHC interact with photons? I wonder how a beam would look from outside. Is there a photo of a proton beam?

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Protons carry charge, so of course they interact with the EM field; while synchrotron radiation isn't as big a problem as with electron/positron colliders (which is why there are plans for next-generation linear accelerators, eg ILC and CLIC), the proton beam does radiate.

Afaik the radiation is detected and used to keep track of the beam, but it's been some time since I talked to someone in the know; I also do not know how images like this are generated, but hopefully someone else here does...

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Is not synchrotron radiation in radio range rather than visible? – Anixx Jul 7 '12 at 12:27
@Anixx Read the first paragraph of the wikipedia entry on synchrotron radiation, the frequency depends on the acceleration and can take on values across the whole of the interesting spectrum. Also note that the beams themselves are pretty good vacumms except at the interaction regions (where they are squeezed into a less diffuse state). – dmckee Jul 7 '12 at 16:45

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