Comment Synchrotron Radiation (Score 1) 219
Not really. If nothing else, with a circular collider the beam can go around multiple times, increasing energy on every pass. The amount of energy you impart is only limited by how strong of a magnetic field you can create to twist the beam.
Sorry but this is simply wrong. Look up synchrotron radiation. For electrons this is a very important effect and your machine energy is limited by how much energy you can give to the electrons on each orbit of the machine. Even for the protons in the LHC this is a noticeable, but not energy limiting, effect.