Fermilab - Accelerators

Accelerators

The first stage in the acceleration process takes place in the Cockcroft–Walton generator. It involves taking hydrogen gas and turning it into H− ions by introducing it into a container lined with molybdenum electrodes: a matchbox-sized, oval-shaped cathode and a surrounding anode, separated by 1 mm and held in place by glass ceramic insulators. A magnetron is used to generate a plasma to form H− near the metal surface. A 750 keV electrostatic field is applied by the Cockcroft–Walton generator, and the ions are accelerated out of the container. The next step is the linear accelerator (or linac), which accelerates the particles to 400 MeV, or about 70% of the speed of light. Right before entering the next accelerator, the H− ions pass through a carbon foil, becoming H+ ions (protons).

The next step is the booster ring. The booster ring is a 468 m circumference circular accelerator that uses magnets to bend beams of protons in a circular path. The protons coming from the Linac travel around the Booster about 20,000 times in 33 milliseconds so that they repeatedly experience electric fields. With each revolution the protons pick up more energy, leaving the Booster with 8 GeV. The Main Injector is the next link in the accelerator chain. Completed in 1999, it has become Fermilab's "particle switchyard" with three functions: it accelerates protons, it delivers protons for antiproton production, and it accelerates antiprotons coming from the antiproton source. The final accelerator is the Tevatron. It is the second most powerful particle accelerator in the world (CERN's Large Hadron Collider being the most powerful). Traveling at almost the speed of light, protons and antiprotons circle the Tevatron in opposite directions. Physicists coordinate the beams so that they collide at the centers of two 5,000-ton detectors DØ and CDF inside the Tevatron tunnel at energies of 1.96 TeV, revealing the structure of matter at the smallest scale.

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