[[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|journal=Arkiv för Matematik, Astronomi och Fysik|volume=18|issue=30|year=1924|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]].
