Why particles are going clockwise in most synchrotrons? First I'm sorry for my poor choice of words, I'm not into physics so I'm lacking of appropriate words.
I'm doing some personal research on synchrotrons, synchrotron radiation and all that stuff. It appears that on many synchrotron I looked at, particles in the storage ring are going clockwise. I know that ESRF, Diamond and SOLEIL are going clockwise.
I think there is only at SPRing-8 and SESAME they're going counter-clockwise.
My point is, is there a reason for this ? Interests of going clockwise vs counter-clockwise ?
Thanks,
 A: No fundamental reasons. In fact a number of colliders operate simultaneously with beams in both directions. At the design stage the choice might be driven by civil engineering constraints for instance for the positioning of the  injector.
It is also interesting to note that in existing machines the beam direction can be switched by changing the polarity of the ring or by injecting antiparticles. Clearly at a light source all the light lines will then point in the wrong direction, and/or if a collimation system is present, it may not effectively absorb secondary showers.
The fact that a (booster) ring or a linac can be reversed depends on what kind of accelerating cavities are employed. If travelling waves cavities are in place this will be impossible, but if they use standing waves there is no problem. An example of such booster ring is the CERN PS, which during LEP times was used to accelerate both $e^+$ and $e^-$ alternatively. The Fermilab main injector ring accelerated both protons and antiprotons for the Tevatron. Concerning linac, proposals for recirculating linear accelerator (RLA) in "dogbone" configuration (with particles entering from both sides) were made as a part of the neutrino factory and muon collider.
