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BeamlineBeamlines at synchrotrons are facilities at which researchers get access to synchrotron light, the tunable and high-energy X-ray beams used in synchrotron research. A fully shielded path guides the high-energy X-ray beams from bending magnets or insertion devices in the storage ring to the research station(s). A large synchrotron facility will have many beamlines, each optimised for a particular field of research, such as materials science, crystallography, medical imaging, life sciences etc. 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. Elements used in beamlines for conditioning the beam between the storage ring and the end station include the following: - Window - a thin sheet of metal, often Beryllium, which transmits almost all of the beam, but protects the vacuum within the storage ring from contamination
- Slits - which control the physical width of the beam and its angular spread
- Focusing mirrors - one or more mirrors, which may be flat, bent-flat, or toroidal, which helps to collimate (focus) the beam
- Monochromators - devices based on diffraction by crystals which select particular wavelength bands and absorb other wavelengths - these devices may be tunable
- Spacing tubes - vacuum tubes which provide the proper space between optical elements, and shield any scattered radiation
The combination of beam conditioning devices controls the thermal load at the end station (heating caused by the beam); the spectrum of radiation incident at the end station; and the focus or collimation of the beam. Devices along the beamline which absord significant power from the beam may need to be actively cooled, by water or even by liquid nitrogen. The entire length of a beamline is normally kept under ultra-high vacuum conditions. A typical beamline at a modern synchrotron facility will be 25m to 30m long from the storage ring to the end station, and may cost several hundred thousand 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 budget permits. References Macromolecular Crystallography at Synchrotrons: An Historical Introduction
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