Using Magnets to Keep Protons in Orbits

In a magnetic field pointing vertically upward, protons traveling to your right would sustain a magnetic force toward you, and protons traveling to your left would feel a force away from you. To have the left-moving protons feel a force toward you would require a magnetic field in the opposite direction, downward. Therefore two beams of protons going in opposite directions can follow the same horizontal circular path only if they move through oppositely directed vertical magnetic fields. This can happen only if the two proton beams are in separate beam pipes going through oppositely directed magnetic fields. This can be accomplished either by having seperate beam pipes with oppositely directed magnetic fields or, more cheaply, by using "two-in-one" magnets, as is done for the LHC.