You can't easily reflect the beam, you can only bend it "with a small radius", but then you loose a lot of the energy via synchrotron radiation. You would also

You can't easily reflect the beam, you can only bend it "with a small radius", but then you loose a lot of the energy via synchrotron radiation. You would also need /very/ strong fields. But the basic idea in everything but linear accelerators is the same: You want to reuse the accelerating structure multiple times be recirculating the beam through it many times. Either in a ring/closed loop, like LHC, or in some form of wound up (open) path (Race track mictrotrons, for example)