Accelerators

The term "atom smasher" conjures up fantastic images: a giant hammer; a dimly lit laboratory where white-coated scientists hover over complicated coils of wires and artificial lightning cascades between large polished domes; a mysterious complex of underground tunnels; visions from the movie "Star Wars."

Particle accelerators can come in as mundane and unglamorous forms as the electron "gun" in your TV set, as the portable 50 kilovolt X-ray machine carried by a medic on the battlefield or as a Van de Graff generator whose beam of 1.5 million volt electrons sterilizes 150,000 gallons of sewage per day for use as fertilizer.

On the other hand with present day technology, it would be possible to build a huge ring proton accelerator, of about ten trillion (TeV) volts energy, and use the intense beam of energetic neutrinos it can generate to "X-ray" the earth's core.

A new generation of medium energy electron accelerators produce intense beams of photons in the ultra-violet and X-ray regions of the electromagnetic spectrum. These  tools offer unprecedented opportunities for state-of-the art research in materials science, biology, chemistry, physics, and the environmental sciences. There is much interesting information on the applications of these machines at the web sites of Lawrence Berkley National Laboratory's Advanced Light Source and Argonne National Laboratory's Advanced Photon Source.

"Smashing" atoms (ionization) requires very little energy. Particle accelerators are machines that accelerate charged particles to high energies, generally high enough (millions of volts) to "smash" or study the nuclei of atoms. As energies surpass a few billion volts (GeV) accelerators become probes of the elementary constituents of matter, quarks and leptons. Beams from the accelerator interact with targets, energy is converted into mass, and new particles can be created and studied.

By creating collisions between beams of particles travelling in opposite directions, extremely high energies corresponding to very high temperatures in the collision are attained. The study of matter in these extreme conditions can be related to the behavior of the universe in the earliest instant after its creation.

By studying accelerators one can learn classical concepts in electricity and magnetism and the motion of charged particles in electromagnetic fields. The simple proportionality between radius of curvature, momentum (in appropriate atomic units), and magnetic field can be illustrated by discussing the size of the Fermilab collider and current suggestions to raise its energy.

Learning an appreciation for orders of magnitude can be done with fun examples such as comparing the kinetic energy of a fly with that of a proton at Fermilab, by comparing the energy of one nucleon in the fly's body with one quark in the high-energy proton beam, by working through the size and cost of a 20 TeV flashlight cell linear accelerator and then comparing that cost with the cost of the future large hadron collider at CERN. The analogy between the focussing of charged-particle beams with quadrupoles and the focussing of light with optical lenses can be used to enhance understanding of both phenomena.

There now exist two antimatter "bottles," one at Fermilab and one at CERN, where a combination of accelerator technologies are used to create and store microscopic quantities of antiprotons. The antiprotons are used in a variety of "frontier" experiments in particle physics.

by Ernie Malamud