In accelerator physics, a beamline refers to the trajectory of the beam of accelerated particles, including the overall construction of the path segment (vacuum tube, magnets, diagnostic devices) along a specific path of an accelerator facility. This part is either

Beamlines usually end in experimental stations that utilize particle beams or synchrotron light obtained from a synchrotron, or neutrons from a spallation source or research reactor. Beamlines are used in experiments in particle physics, materials science, chemistry, and molecular biology.

Beamline in a particle accelerator

It is impossible to see the beam pipe on this beamline. However the section of the big beam pipe is used with a grid system for alignment with a laser, known as the laser pipe. This particular beamline is approximately 3 kilometers long.

In particle accelerators the beamline is usually housed in a tunnel and/or underground, cased inside a concrete housing. The beamline is usually a cylindrical metal pipe, typically called a beam pipe, and/or a drift tube, evacuated to a high vacuum so there are few gas molecules in the path for the beam of accelerated particles to hit, which would scatter them before they reach their destination.

There are specialized devices and equipment on the beamline that are used for producing, maintaining, monitoring, and accelerating the particle beam. These devices may be in proximity or attached to the beamline. These devices include sophisticated transducers, diagnostics (position monitors and wire scanners), lenses, collimators, thermocouples, ion pumps, ion gauges, ion chambers (sometimes called "beam loss monitors"), vacuum valves ("isolation valves"), and gate valves, to mention a few. There are also water cooling devices to cool the dipole and quadrupole magnets. Positive pressure, such as that provided by compressed air, regulates and controls the vacuum valves and manipulators on the beamline.

It is imperative to have all beamline sections, magnets, etc., aligned by a survey and alignment crew by using a laser tracker. All beamlines must be within micrometre tolerance. Good alignment helps to prevent beam loss, and beam from colliding with the pipe walls, which creates secondary emissions and/or radiation.