Thomas Jefferson National Accelerator Facility
| Thomas Jefferson National Accelerator Facility ： ウィキペディア英語版|
Thomas Jefferson National Accelerator Facility (TJNAF), commonly called Jefferson Lab or JLab, is a U.S. national laboratory located in Newport News, Virginia. Since June 1, 2006, it has been operated by Jefferson Science Associates, LLC, a joint venture between Southeastern Universities Research Association, Inc., and CSC Applied Technologies, LLC. Until 1996 it was known as the Continuous Electron Beam Accelerator Facility (CEBAF); commonly, this name is still used for the main accelerator.
Founded in 1984, Jefferson Lab employs more than 675 people and more than 2,000 scientists from around the world have conducted research using the facility. Its stated mission is "to provide forefront scientific facilities, opportunities and leadership essential for discovering the fundamental structure of nuclear matter; to partner in industry to apply its advanced technology; and to serve the nation and its communities through education and public outreach."
The laboratory's main research facility is the CEBAF accelerator, which consists of a polarized electron source and injector and a pair of superconducting RF linear accelerators that are 7/8-mile (1400 m) in length and connected to each other by two arc sections that contain steering magnets. As the electron beam makes up to five successive orbits, its energy is increased up to a maximum of 6 GeV. This leads to a design that appears similar to a racetrack when compared to the classical ring-shaped accelerators found at sites such as CERN or Fermilab. Effectively, CEBAF is a linear accelerator, similar to SLAC at Stanford, that has been folded up to a tenth of its normal length.
The design of CEBAF allows the electron beam to be continuous rather than the pulsed beam typical of ring shaped accelerators. (There is some beam structure, but the pulses are very much shorter and closer together.) The electron beam is directed onto three potential targets (see below). One of the distinguishing features of Jefferson Lab is the continuous nature of the electron beam, with a bunch length of less than 1 picosecond. Another is Jefferson Lab's use of superconducting RF (SRF) technology, which uses liquid helium to cool niobium to approximately 4 K (−452.5 °F), removing electrical resistance and allowing the most efficient transfer of energy to an electron. To achieve this, Jefferson Lab houses the world's largest liquid helium refrigerator, and it was one of the first large-scale implementators of SRF technology. The accelerator is built 8 meters below the Earth's surface, or approximately 25 feet, and the walls of the accelerator tunnels are 2 feet thick.
The beam ends in three experimental halls, labelled Hall A, Hall B, and Hall C. Each hall contains a unique spectrometer to record the results of collision between the electron beam and a stationary target. This allows physicists to study the structure of the atomic nucleus, specifically the interaction of the quarks that make up protons and neutrons of the nucleus.
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