Another constraint on circular accelerators is the large magnetic fields needed to keep the particles going in circular paths. The presence of a magnetic field does not add or subtract energy from the particles. The magnetic field only bends the particles along the arc of the accelerator. Magnets are also used to direct charged particle beams toward targets and to "focus" the beams, just as optical lenses focus light.
If a magnetic field makes electrons go clockwise, in which direction does it make positrons go?