Linear particle accelerator: Difference between revisions

Revision as of 23:43, 21 November 2022

Revision as of 11:24, 30 May 2023

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[[Image:Aust.-Synchrotron,-Linac,-14.06.2007.jpg|250px|right|thumb|The linac within the [[Australian Synchrotron]] uses [[radio waves]] from a series of [[Resonator#Cavity resonators|RF cavities]] at the start of the linac to accelerate the electron beam in bunches to energies of 100 MeV.]]

A '''linear particle accelerator''' (often shortened to '''linac''') is a type of [[particle accelerator]] that accelerates charged [[subatomic particle]]s or [[ion]]s to a high speed by subjecting them to a series of [[Oscillation|oscillating]] [[electric potential]]s along a [[Line (geometry)|linear]] [[beamline]]. The principles for such machines were proposed by [[Gustav Ising]] in 1924,<ref>{{Cite journal|author=G. Ising: ''|title=Prinzip einer Methode zur Herstellung von Kanalstrahlen hoher Voltzahl.'' In: ''|journal=Arkiv för Matematik, Astronomi och Fysik.'' Band |volume=18, Nr. |issue=30, |year=1924, S. |pages=1–4.}}</ref> while the first machine that worked was constructed by [[Rolf Widerøe]] in 1928<ref>{{cite journal|last = Widerøe|first = R.|author-link=Rolf Widerøe |date = 17 December 1928 |title=Über Ein Neues Prinzip Zur Herstellung Hoher Spannungen|journal = Archiv für Elektronik und Übertragungstechnik|doi = 10.1007/BF01656341 |volume = 21|number = 4|pages = 387–406|s2cid = 109942448}}</ref> at the [[RWTH Aachen University]].<ref>{{cite conference|last1=Bryant |first1=P J |title=A brief history and review of accelerators |conference=5th General Accelerator Physics Course |publisher=CERN Accelerator School |date=1994 |doi=10.5170/CERN-1994-001.1}}</ref><ref>{{cite book |last1=Mangan |first1=Michelangelo |editor1-last=Brüning |editor1-first=Oliver |editor2-last=Myers |editor2-first=Stephen |title=Challenges and goals for accelerators in the XXI century |date=2016 |publisher=World Scientific |___location=Hackensack, New Jersey |isbn=978-981-4436-39-7 |page=33 |url=https://www.worldscientific.com/worldscibooks/10.1142/8635 |chapter=Particle accelerators and the progress of particle physics|doi=10.1142/8635|bibcode=2016cgat.book.....M }}</ref>

Linacs have many applications: they generate [[X-ray]]s and high energy electrons for medicinal purposes in [[radiation therapy]], serve as particle injectors for higher-energy accelerators, and are used directly to achieve the highest kinetic energy for light particles (electrons and positrons) for [[particle physics]].

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=== Compact Linear Collider ===

The concept of the [[Compact Linear Collider]] (CLIC) (original name ''CERN Linear Collider'' , with the same abbreviation) for electrons and positrons provides a traveling wave accelerator for energies of the order of 1 tera-electron volt (TeV).<ref>{{Cite book|last=Raubenheimer|first=T. O.|title=A 3 TeV e+e− linear collider based on CLIC technology|publisher=|year=2000|isbn=92-9083-168-5|___location=Geneva|pages=}}</ref> Instead of the otherwise necessary numerous [[klystron]] amplifiers to generate the acceleration power, a second, parallel electron linear accelerator of lower energy is to be used, which works with superconducting cavities in which standing waves are formed. High-frequency power is extracted from it at regular intervals and transmitted to the main accelerator. In this way, the very high acceleration field strength of 80 MV / m should be achieved.

=== Kielfeld accelerator (plasma accelerator) ===

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===Medical linacs===

[[Image:External beam radiotherapy retinoblastoma nci-vol-1924-300.jpg|thumb|left|Historical image showing Gordon Isaacs, the first patient treated for [[retinoblastoma]] with linear accelerator radiation therapy (in this case an electron beam), in 1957, in the U.S. Other patients had been treated by linac for other diseases since 1953 in the UK. Gordon's right eye was removed on January 11, 1957 because cancer had spread there. His left eye, however, had only a localized tumor that prompted [[Henry Kaplan (physician)|Henry Kaplan]] to treat it with the electron beam.]]

Linac-based [[radiation therapy]] for cancer treatment began with the first patient treated in 1953 in London, UK, at the [[Hammersmith Hospital]], with an 8&nbsp;MV machine built by [[Metropolitan-Vickers]] and installed in 1952, as the first dedicated medical linac.<ref>{{Cite journal|author=Thwaites, DI and Tuohy J, |title=Back to the future: the history and development of the clinical linear accelerator, |journal=Phys. Med. Biol. |volume=51 (|year=2006) |pages=R343–R36, | doi:=10.1088/0031-9155/51/13/R20</ref><ref>[http://www.ampi-nc.org/essayresult/LINAC-3.pdf LINAC-3, Advances in Medical Linear Accelerator Technology]. ampi-nc.org. Unavailable 25 Feb 2021.}}</ref> A short while later in 1954, a 6&nbsp;MV linac was installed in Stanford, USA, which began treatments in 1956.

[[Medical linear accelerators]] accelerate electrons using a tuned-cavity waveguide, in which the RF power creates a [[standing wave]]. Some linacs have short, vertically mounted waveguides, while higher energy machines tend to have a horizontal, longer waveguide and a bending magnet to turn the beam vertically towards the patient. Medical linacs use monoenergetic electron beams between 4 and 25&nbsp;MeV, giving an X-ray output with a spectrum of energies up to and including the electron energy when the electrons are directed at a high-density (such as [[tungsten]]) target. The electrons or X-rays can be used to treat both benign and malignant disease. The LINAC produces a reliable, flexible and accurate radiation beam. The versatility of LINAC is a potential advantage over [[cobalt therapy]] as a treatment tool. In addition, the device can simply be powered off when not in use; there is no source requiring heavy shielding – although the treatment room itself requires considerable shielding of the walls, doors, ceiling etc. to prevent escape of scattered radiation. Prolonged use of high powered (>18&nbsp;MeV) machines can induce a significant amount of radiation within the metal parts of the head of the machine after power to the machine has been removed (i.e. they become an active source and the necessary precautions must be observed).