The Tevatron is a colliding accelerator. It receives its beam, either protons or antiprotons, from the Main Injector. A normal shot setup consists of injecting bunches of protons followed by antiprotons into the TeV. These two "trains" of particles, protons and antiprotons, are accelerated in opposite directions and then forced to collide at certain points around the ring. The Tevatron can send beam, protons or antiprotons, back to the Main Injector.