Fermi National Accelerator Laboratory (Fermilab) is located about 40km west of downtown Chicago.  It hosts the Tevatron proton-antiproton accelerator, a storage ring with a circumference of about 6.3km.  At the two Tevatron experiments CDF and D0, protons and antiprotons collide at a center-of-mass energy of 1.96TeV and at a rate of 2.5MHz. The picture below shows both the Tevatron (in the rear) and a second ring, which is part of the pre-accelerator and antiproton recycling system.