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What's used to steer Jefferson Lab's electron beam?

Although it may not look like it at first, the Jefferson Lab accelerator really works much like your TV set. Electrons are accelerated to higher energies by precision-tuned ever-changing electrical fields (the "RF fields"). To steer them, one uses electromagnets to push them to the side (or vertically). The basic type is the "dipole" with a "north" and "south" pole. They act much like a prism does with light. A prism will bend white light and separate it into its different colors. The dipole magnet will "bend" the electron beam and separate the electrons of differing energy. As in life, nothing is that simple, so one also has to use "quadrupole" (two sets of north and south poles) and "sextupole" (six poles) magnets to keep the beam focused just as lenses are used to focus light.

The electron beam begins its first orbit at the injector and proceeds through the underground race track-shaped accelerator tunnel at nearly the speed of light. The accelerator uses superconducting radio-frequency technology to drive electrons to higher and higher energies. A refrigeration plant, called the Central Helium Liquefier or CHL, provides liquid helium for ultra-low-temperature (-456°F) superconducting operation. After the electrons are accelerated around Jefferson Lab's accelerator, they are steered by the electromagnets in the "beam switchyard" into the three Halls. The electron beam can be split for use by three simultaneous experiments in the end stations, which are circular, domed chambers with diameters ranging from 98 to 172 feet. Special equipment in each hall records the interactions between incoming electrons and the target materials. A continuous electron beam is necessary to accumulate data at an efficient rate yet ensure that each interaction is separate enough to be fully observed.


Carl Zorn, Detector Scientist (Other answers by Carl Zorn)

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