Editing Charged particle beam

{{Short description|Spatially localized group of electrically charged particles travelling in same direction}}
{{Refimprove|date=January 2008}}
A '''charged particle beam''' is a spatially localized group of [[electric charge|electrically charge]]d [[Subatomic particle|particle]]s that have approximately the same [[Position (geometry)|position]], [[kinetic energy]] (resulting in the same [[velocity]]), and direction. The kinetic energies of the particles are much larger than the energies of particles at [[ambient temperature]]. The high energy and [[wikt:directionality|directionality]] of charged particle beams make them useful for many applications in [[particle physics]] (see [[Particle beam#Applications]] and [[Electron-beam technology]]).

Such beams can be split into two main classes:
# ''unbunched beams'' (''coasting beams''<ref>{{Citation|last1=Ruggiero|first1=F|title=CERN Accelerator School: Basic Course On General Accelerator Physics|date=June 2005|url=https://cds.cern.ch/record/425460|pages=296|doi=10.5170/CERN-2005-004|id=CERN-2005-004|last2=Thomashausen|first2=J|accessdate=14 November 2017}}</ref> or ''DC beams''), which have no longitudinal substructure in the direction of beam motion. 
# ''bunched beams'', in which the particles are distributed into [[Pulse (physics)|pulses]] (bunches) of particles. Bunched beams are most common in modern facilities, since the most modern [[Particle accelerator|particle accelerators]] require bunched beams for acceleration.<ref name="Edwards">{{Cite book
|title=An Introduction to the Physics of High Energy Accelerators
|publisher=Wiley-VCH
|location=Weinheim, Germany
|first1=D.A. |last1=Edwards
|first2=M.J. |last2=Syphers
|date=1993
|isbn=9780471551638
}}</ref>

Assuming a [[normal distribution]] of particle positions and impulses, a charged particle beam (or a bunch of the beam) is characterized by<ref name="humphries">{{Cite book
 |title= Charged particle beams
 |publisher= [[Wiley-Interscience]]
 |location= New York
 |first1= Stanley |last1 = Humphries
 |date= 1990
 |isbn= 9780471600145
 |url = http://www.fieldp.com/freeware/charged_particle.pdf
}}</ref>
* the species of particle, e.g. [[electrons]], [[proton]]s, or [[atomic nucleus|atomic nuclei]]
* the mean [[energy]] of the particles, often expressed in [[electronvolt]]s (typically keV to GeV)
* the (average) particle current, often expressed in [[ampere]]s
* the particle beam size, often using the so-called ''β-function''
* the [[beam emittance]], a measure of the area occupied by the beam in one of several [[phase space]]s.

These parameters can be expressed in various ways. For example, the current and beam size can be combined into the [[current density]], and the current and energy (or beam voltage V) can be combined into the [[perveance]] ''K'' = ''I'' ''V''<sup>−3/2</sup>.

The charged [[particle beam]]s that can be manipulated in [[particle accelerator]]s can be subdivided into [[electron beam]]s, [[ion beam]]s and [[proton beam]]s.

==Common types==
* [[Electron beam]] such as in a [[scanning electron microscope]], in accelerators such as the [[Large Electron–Positron Collider]], [[synchrotron light source]]s, or in [[cathode ray tubes]]
* Proton beam, such as the beams used in [[proton therapy]], at colliders such as the [[Tevatron]] and the [[Large Hadron Collider]], or for [[proton beam writing]] in lithography.
* [[Ion beam]]s, such as at the [[Relativistic Heavy Ion Collider]] or the [[Facility for Rare Isotope Beams]].

==References==
<references/>

[[Category:Accelerator physics]]
[[Category:Experimental particle physics]]