Beamline

In accelerator physics, a beamline refers to the trajectory of the beam of accelerated 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 In accelerator physics, a beamline refers to the trajectory of the beam of accelerated 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 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, 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. Good alignment helps to prevent beam loss, and beam from colliding with the pipe walls, which creates secondary emissions and/or radiation. Regarding synchrotrons, beamline may also refer to the instrumentation that carries beams of synchrotron radiation to an experimental end station, which uses the radiation produced by the bending magnets and insertion devices in the storage ring of a synchrotron radiation facility. A typical application for this kind of beamline is crystallography, although many other techniques utilising synchrotron light exist. At a large synchrotron facility there will be many beamlines, each optimised for a particular field of research. The differences will depend on the type of insertion device (which, in turn, determines the intensity and spectral distribution of the radiation); the beam conditioning equipment; and the experimental end station. A typical beamline at a modern synchrotron facility will be 25 to 100 m long from the storage ring to the end station, and may cost up to millions of US dollars. For this reason, a synchrotron facility is often built in stages, with the first few beamlines opening on day one of operation, and other beamlines being added later as the funding permits. The beamline elements are located in radiation shielding enclosures, called hutches, which are the size of a small room (cabin). A typical beamline consists of two hutches, an optical hutch for the beam conditioning elements and an experimental hutch, which houses the experiment. Between hutches, the beam travels in a transport tube. Entrance to the hutches is forbidden when the beam shutter is open and radiation can enter the hutch. This is enforced by the use of elaborate safety systems with redundant interlocking functions, which make sure that no one is inside the hutch when the radiation is turned on. The safety system will also shut down the radiation beam if the door to the hutch is accidentally opened when the beam is on. In this case, the beam is dumped, meaning the stored beam is diverted into a target designed to absorb and contain its energy.