Thomas Jefferson National Accelerator Facility - Accelerator

Accelerator

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 7/8 mile (1400 m) in length, connected to each other by two arc sections which 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, compared to the classical ring shaped accelerator shape found at sites such as CERN or Fermilab. Effectively, CEBAF is a linear accelerator, like 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 JLab is the continuous nature of the electron beam, with a bunch length of less than 1 picosecond. Another is JLab'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, JLab houses the world's largest liquid helium refrigerator, and was one of the first large-scale implementators of SRF technology. The accelerator is built 8 meters, or approximately 25 feet, below the Earth's surface, 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.