In accelerator physics, a beamline refers to the trajectory of the beam of particles, including the overall construction of the path segment (guide tubes, diagnostic devices) along a specific path of an accelerator facility. This part is either the line in a linear accelerator along which a beam of particles travels, or the path leading from particle generator (e.g. a cyclic accelerator, synchrotron light sources, cyclotrons, or spallation sources) to the experimental end-station. 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, life science, chemistry, and molecular biology, but can also be used for irradiation tests or to produce isotopes. In particle accelerators the beamline is usually housed in a tunnel and/or underground, cased inside a concrete housing for shielding purposes. 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 otherwise could 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 of or attached directly to the beamline. These devices include sophisticated transducers, diagnostics (position monitors and wire scanners), lenses, collimators, thermocouples, ion pumps, ion gauges, ion chambers (for diagnostic purposes; usually called "beam monitors"), vacuum valves ("isolation valves"), and gate valves, to mention a few. It is imperative to have all beamline sections, magnets, etc., aligned (often by a survey and an alignment crew by using a laser tracker), beamlines must be within micrometre tolerance.