To keep any object going in a circle, there needs to be a constant force on that object towards the center of the circle. In a circular accelerator, an electric field makes the charged particle accelerate, while large magnets provide the necessary inward force to bend the particle's path in a circle. (In the image to the left, the particle's velocity is represented by the white arrow, while the inward force supplied by the magnet is the yellow arrow.)

The presence of a magnetic field does not add or subtract energy from the particles. The magnetic field only bends the particles' paths 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.

Question: If a magnetic field makes electrons go clockwise, in which direction does it make positrons go? [ Answer ]