A particle beam is a stream of charged or neutral particles other than

photons A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that ...

. In

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

, these particles can move with a velocity close to the

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant exactly equal to ). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time i ...

. There is a difference between the creation and control of charged particle beams and neutral particle beams, as only the first type can be manipulated to a sufficient extent by devices based on

electromagnetism In physics, electromagnetism is an interaction that occurs between particles with electric charge via electromagnetic fields. The electromagnetic force is one of the four fundamental forces of nature. It is the dominant force in the interacti ...

. The manipulation and diagnostics of charged particle beams at high kinetic energies using

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

s are main topics of

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 ...

Sources

Charged particles such as

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

positron The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...

s, and

proton A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...

s may be separated from their common surroundings. This can be accomplished by processes such as

thermionic emission Thermionic emission is the liberation of charged particles from a hot electrode whose thermal energy gives some particles enough kinetic energy to escape the material's surface. The particles, sometimes called ''thermions'' in early literature, a ...

arc discharge An electric arc (or arc discharge) is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma, which may produce visible light. An ...

. The following devices are commonly used as sources for particle beams: *

Ion source An ion source is a device that creates atomic and molecular ions. Ion sources are used to form ions for mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters and ion engines. Electron ionization Elect ...

Cathode-ray tube A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms on an oscilloscope, a ...

, or more specifically in one of its parts called electron gun. This is also part of traditional television and computer screens. * Photocathodes may also be built in as a part of an electron gun, using the

photoelectric effect The photoelectric effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physi ...

to separate particles from their substrate. *

Neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

beams may be created by energetic proton beams which impact on a target, e.g. of

beryllium Beryllium is a chemical element; it has Symbol (chemistry), symbol Be and atomic number 4. It is a steel-gray, hard, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with ...

material. (see article Particle therapy) * Bursting a petawatt laser onto a

titanium Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...

foil to produce a proton beam.

Manipulation

Acceleration

Charged beams may be further accelerated by use of high resonant, sometimes also

superconducting Superconductivity is a set of physical properties observed in superconductors: materials where electrical resistance vanishes and magnetic fields are expelled from the material. Unlike an ordinary metallic conductor, whose resistance decreases g ...

, microwave cavities. These devices accelerate particles by interaction with an

electromagnetic field An electromagnetic field (also EM field) is a physical field, varying in space and time, that represents the electric and magnetic influences generated by and acting upon electric charges. The field at any point in space and time can be regarde ...

. Since the

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

of hollow macroscopic, conducting devices is in the

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the u ...

(RF) band, the design of such cavities and other RF devices is also a part of accelerator physics. More recently,

plasma acceleration Plasma acceleration is a technique for accelerating charged particles, such as electrons or ions, using the electric field associated with an electron plasma wave or other high-gradient plasma structures. These structures are created using eithe ...

has emerged as a possibility to accelerate particles in a plasma medium, using the

electromagnetic energy In physics, and in particular as measured by radiometry, radiant energy is the energy of electromagnetic and gravitational radiation. As energy, its SI unit is the joule (J). The quantity of radiant energy may be calculated by integrating radia ...

of pulsed high-power

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...

systems or the

kinetic energy In physics, the kinetic energy of an object is the form of energy that it possesses due to its motion. In classical mechanics, the kinetic energy of a non-rotating object of mass ''m'' traveling at a speed ''v'' is \fracmv^2.Resnick, Rober ...

of other charged particles. This technique is under active development, but cannot provide reliable beams of sufficient quality at present.

Guidance

In all cases, the beam is steered with dipole magnets and focused with quadrupole magnets. With the end goal of reaching the desired position and beam spot size in the experiment.

Applications

High-energy physics

High-energy particle beams are used for

particle physics Particle physics or high-energy physics is the study of Elementary particle, fundamental particles and fundamental interaction, forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the s ...

experiments in large facilities; the most common examples being the

Large Hadron Collider The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It was built by the CERN, European Organization for Nuclear Research (CERN) between 1998 and 2008, in collaboration with over 10,000 scientists, ...

and the

Tevatron The Tevatron was a circular particle accelerator (active until 2011) in the United States, at the Fermilab, Fermi National Accelerator Laboratory (called ''Fermilab''), east of Batavia, Illinois, and was the highest energy particle collider unt ...

Synchrotron radiation

Electron beam Since the mid-20th century, electron-beam technology has provided the basis for a variety of novel and specialized applications in semiconductor manufacturing, microelectromechanical systems, nanoelectromechanical systems, and microscopy. Mechani ...

s are employed in synchrotron light sources to produce X-ray radiation with a continuous

spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...

over a wide

frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

band which is called synchrotron radiation. This X-ray radiation is used at beamlines of the synchrotron light sources for a variety of spectroscopies ( XAS, XANES, EXAFS, ''μ''-XRF, ''μ''-XRD) in order to probe and to characterize the structure and the chemical speciation of solids and biological materials.

Particle therapy

Energetic particle beams consisting of

protons A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' ( elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an electron (the pro ...

, neutrons, or positive

ions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

(also called particle microbeams) may also be used for cancer treatment in particle therapy. Linear accelerators use electron beam at near speed of light to treat deep cancers in patients. A tungsten/molybdenum target can be moved into the beam to create x-rays to treat surface cancers.

Astrophysics and space physics

Many phenomena in astrophysics are attributed to particle beams of various kinds. Solar Type III radio bursts, the most common impulsive radio signatures from the Sun, are used by scientists as a tool to better understand solar accelerated electron beams. Additionally, particle beams cause instabilities when interacting with plasma, which may lead to conditions causing electrostatic solitary waves.

Military

The U.S. Advanced Research Projects Agency started work on

particle beam weapon A particle-beam weapon uses a high-energy beam of atomic or subatomic particles to damage the target by disrupting its atomic and/or molecular structure. A particle-beam weapon is a type of space-based directed-energy weapon, which directs fo ...

s in 1958. The general idea of such weaponry is to hit a target object with a stream of accelerated particles with high

, which is then transferred to the atoms, or molecules, of the target. The power needed to project a high-powered beam of this kind surpasses the production capabilities of any standard battlefield powerplant, thus such weapons are not anticipated to be produced in the foreseeable future.

References

{{DEFAULTSORT:Particle Beam Accelerator physics pt:Feixe (física)