accelerator physics Accelerator physics is a branch of applied physics, concerned with designing, building and operating particle accelerators. As such, it can be described as the study of motion, manipulation and observation of relativistic charged particle beams ...

, 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 A linear particle accelerator (often shortened to linac) is a type of particle accelerator that accelerates charged subatomic particles or ions to a high speed by subjecting them to a series of oscillating electric potentials along a linear ...

along which a beam of particles travels, or * the path leading from particle generator (e.g. a cyclic accelerator, synchrotron light sources,

cyclotron A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Jan ...

s, or spallation sources) to the experimental end-station. Beamlines usually end in experimental stations that utilize particle beams or

synchrotron light Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in ...

obtained from a

synchrotron A synchrotron is a particular type of cyclic particle accelerator, descended from the cyclotron, in which the accelerating particle beam travels around a fixed closed-loop path. The magnetic field which bends the particle beam into its closed ...

, or

neutrons The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave ...

from a spallation source or

research reactor Research reactors are nuclear fission-based nuclear reactors that serve primarily as a neutron source. They are also called non-power reactors, in contrast to power reactors that are used for electricity production, heat generation, or marit ...

. Beamlines are used in experiments in

particle physics Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) an ...

, materials science,

life science Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from that which does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energy ...

chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...

, and

molecular biology Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and phys ...

, but can also be used for irradiation tests or to produce isotopes.

Beamline in a particle accelerator

particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams. Large accelerators are used for fundamental research in particle ...

s 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 A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...

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

transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and con ...

s, diagnostics (position monitors and wire scanners), lenses,

collimator A collimator is a device which narrows a beam of particles or waves. To narrow can mean either to cause the directions of motion to become more aligned in a specific direction (i.e., make collimated light or parallel rays), or to cause the spati ...

thermocouple A thermocouple, also known as a "thermoelectrical thermometer", is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of th ...

s, 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 The micrometre (American and British English spelling differences#-re, -er, international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American and British English spelling differences# ...

tolerance. Good alignment helps to prevent beam loss, and beam from colliding with the pipe walls, which creates

secondary emission In particle physics, secondary emission is a phenomenon where primary incident particles of sufficient energy, when hitting a surface or passing through some material, induce the emission of secondary particles. The term often refers to the em ...

s and/or

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

Synchrotron radiation beamline

Regarding

s, ''beamline'' may also refer to the instrumentation that carries beams of

synchrotron radiation Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in ...

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 Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids. Crystallography is a fundamental subject in the fields of materials science and solid-state physics ( condensed matter physics). The wor ...

, although many other techniques utilising

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. Elements that are used in beamlines by experimenters for conditioning the radiation beam between the storage ring and the end station include the following: *Windows: windows are used to separate UHV and HV vacuum sections and to terminate the beamline. They are also used between UHV vacuum sections to provide protection from vacuum accidents. The foils used for the window membrane also attenuate the radiation spectrum in the region below 6KeV. 1- Beryllium Windows: Beryllium windows can be supplied cooled, or uncooled, with various sizes (and numbers) of window apertures. Windows are sized to suit specific requirements, however the maximum size of a window is determined by the foil thickness and pressure differential to be withstood. Windows can be supplied fitted with a range of beam entry/exit flange sizes to suite specific requirements. 2- CVD Diamond Windows: Chemical Vapour Deposition (CVD) Diamond offer extreme hardness, high thermal conductivity, chemical inertness, and high transparency over a very wide spectral range. Stronger and stiffer than Beryllium, with lower thermal expansion and lower toxicity, it is ideal for UHV isolation windows in X-ray beamlines. Windows can be supplied embedded in UHV flanges and with efficient water cooling. 3- Exit Windows: Vacuum exit windows come in a variety of materials including Beryllium and CVD diamond detailed above. *Slits: Slits are used to define the beam either horizontally or vertically. They can be used in pairs to define the beam in both directions. the maximum aperture size is selected to suit specific requirements. Options include cooled (white beam operation) or uncooled (monochromatic beam operation) slits and phosphor coating on the upstream side of the slit to assist with beam location. There are four main type of slits: Blade Slits, High Heat Load Slits, Inline Slits, High Precision Slits. *Shutters: Beam shutters are used to interrupt radiation from the front end, or optics enclosures when it is not required downstream. They have an equipment and personnel safety function. And there are three types of shutters; Photon Shutters, Monochromatic Beam Shutters, Custom Shutters *Beam Filters: (or attenuators) remove unwanted energy ranges from the beam by passing the incident synchrotron radiation through a thin transmissive foil. They are often used to manage heat-loads of white beams to optimize beamline performance according to the energy of operation. A typical filter has two or three racks, with each rack holding three of four separate foils, depending upon the beam cross-section. *Focusing mirrors - one or more mirrors, which may be flat, bent-flat, or toroidal, which helps to

collimate A collimated beam of light or other electromagnetic radiation has parallel rays, and therefore will spread minimally as it propagates. A perfectly collimated light beam, with no divergence, would not disperse with distance. However, diffraction ...

(focus) the beam *Monochromators - devices based on

diffraction Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a s ...

by crystals which select particular

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tr ...

bands and absorb other wavelengths, and which are sometimes tunable to varying wavelengths, and sometimes fixed to a particular wavelength *Spacing tubes - vacuum maintaining tubes which provide the proper space between optical elements, and shield any scattered radiation *Sample stages - for mounting and manipulating the sample under study and subjecting it to various external conditions, such a varying temperature, pressure etc. *Radiation detectors - for measuring the radiation which has interacted with the sample The combination of beam conditioning devices controls the

thermal load A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

(heating caused by the beam) at the end station; the spectrum of radiation incident at the end station; and the focus or collimation of the beam. Devices along the beamline which absorb significant power from the beam may need to be actively cooled by water, or

liquid nitrogen Liquid nitrogen—LN2—is nitrogen in a liquid state at low temperature. Liquid nitrogen has a boiling point of about . It is produced industrially by fractional distillation of liquid air. It is a colorless, low viscosity liquid that is wid ...

. The entire length of a beamline is normally kept under ultra high vacuum conditions.

Software for beamline modeling

Although the design of a synchrotron radiation beamline may be seen as an application of X-ray optics, there are dedicated tools for modeling the x-ray propagation down the beamline and their interaction with various components. There are ray-tracing codes such a
Shadow
an
McXTrace
that treat the x-ray beam in the geometric optics limit, and then there are wave propagation software that takes into account diffraction, and the intrinsic wavelike properties of the radiation. For the purposes of understanding full or partial coherence of the synchrotron radiation, the wave properties need to be taken into account. The code
SRWSpectra
an
xrt
include this possibility, the latter code supports "hybryd" regime allowing to switch from geometric to wave approach on a given optical segment.

Neutron beamline

Superficially, neutron beamlines differ from synchrotron radiation beamlines mostly by the fact that they use neutrons from a

or a spallation source instead of photons. Since neutrons don't carry charge and are difficult to redirect, the components are quite different (see e.g. choppers or neutron super mirrors). The experiments usually measure

neutron scattering Neutron scattering, the irregular dispersal of free neutrons by matter, can refer to either the naturally occurring physical process itself or to the man-made experimental techniques that use the natural process for investigating materials. Th ...

from or energy transfer to the sample under study.

References

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External links