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 In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass. They vary greatly in size or quantity, from s ...

travels, or * the path leading from particle generator (e.g. a cyclic accelerator,

synchrotron light source A synchrotron light source is a source of electromagnetic radiation (EM) usually produced by a storage ring, for scientific and technical purposes. First observed in synchrotrons, synchrotron light is now produced by storage rings and other ...

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 beam A particle beam is a stream of charged or neutral particles. In particle accelerators, these particles can move with a velocity close to the speed of light. There is a difference between the creation and control of charged particle beams and ne ...

s or synchrotron light obtained from a synchrotron, or neutrons 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 t ...

, chemistry, 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 physi ...

, 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 di ...

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 cont ...

s, diagnostics (position monitors and

wire scanner Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm A wire is a flexible strand of metal. Wire is co ...

s), 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 ...

ion pump An ion pump (also referred to as a sputter ion pump) is a type of vacuum pump which operates by sputtering a metal getter. Under ideal conditions, ion pumps are capable of reaching pressures as low as 10−11 mbar. An ion pump first ionizes ga ...

ion gauge Pressure measurement is the measurement of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressur ...

s, ion chambers (for diagnostic purposes; usually called "beam monitors"), vacuum valves ("isolation valves"), and

gate valve A gate valve, also known as a sluice valve, is a valve that opens by lifting a barrier (gate) out of the path of the fluid. Gate valves require very little space along the pipe axis and hardly restrict the flow of fluid when the gate is fully ope ...

s, to mention a few. It is imperative to have all beamline sections, magnets, etc., aligned (often by a

survey Survey may refer to: Statistics and human research * Statistical survey, a method for collecting quantitative information about items in a population * Survey (human research), including opinion polls Spatial measurement * Surveying, the techniq ...

and an alignment crew by using a

laser tracker {{Short description, Instruments that accurately measure large objects Laser trackers are instruments that accurately measure large objects by determining the positions of optical targets held against those objects. The accuracy of laser tracker ...

), beamlines must be within

micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

tolerance. Good alignment helps to prevent beam loss, and beam from colliding with the pipe walls, which creates secondary emissions and/or radiation.

Synchrotron radiation beamline

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 device An insertion device (ID) is a component in modern synchrotron light sources, so called because they are "inserted" into accelerator tracks. They are periodic magnetic structures that stimulate highly brilliant, forward-directed synchrotron radiati ...

s in the

storage ring A storage ring is a type of circular particle accelerator in which a continuous or pulsed particle beam may be kept circulating typically for many hours. Storage of a particular particle depends upon the mass, momentum and usually the charge of t ...

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

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

toroid In mathematics, a toroid is a surface of revolution with a hole in the middle. The axis of revolution passes through the hole and so does not intersect the surface. For example, when a rectangle is rotated around an axis parallel to one of its ...

al, 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 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, t ...

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 (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. The entire length of a beamline is normally kept under

ultra high vacuum Ultra-high vacuum (UHV) is the vacuum regime characterised by pressures lower than about . UHV conditions are created by pumping the gas out of a UHV chamber. At these low pressures the mean free path of a gas molecule is greater than approximately ...

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

{{reflist

External links

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Accelerator physics Synchrotron instrumentation Neutron instrumentation Materials science Life_sciences