Editing Cyclotron (section)

== History ==

[[File:4-inch-cyclotron.jpg|thumb|upright=1.3|Lawrence's original {{convert|4.5|in|cm|adj=on}} cyclotron]]
[[File:Berkeley_60-inch_cyclotron.jpg|thumb|upright=1.3|Lawrence's {{convert|60|in|cm|adj=on}} cyclotron at [[Lawrence Radiation Laboratory]], [[University of California]], Berkeley, California, constructed in 1939. The magnet is on the left, with the vacuum chamber between its pole pieces, and the beamline which analyzed the particles is on the right.]]

=== Origins ===
A key limitation of the earliest charged particle accelerators was that increasing the particle energy required extending the length of the acceleration path, which was only feasible and practical up to a certain point. In 1927, while a student at Kiel, German physicist [[Max Steenbeck]] was the first to formulate the concept of the cyclotron, but he was discouraged from pursuing the idea further.<ref>[http://ark.cdlib.org/ark:/13030/ft5s200764/ Lawrence and His Laboratory] - ''II — A Million Volts or Bust'' 81–82 in Heilbron, J. L., and Robert W. Seidel ''Lawrence and His Laboratory: A History of the Lawrence Berkeley Laboratory', Volume I.'' (Berkeley:  University of California Press, 2000)</ref> In late 1928 and early 1929, Hungarian physicist [[Leo Szilárd]] filed patent applications in Germany for the [[linear accelerator]], cyclotron, and [[betatron]].<ref name="Dannen-20012">{{cite journal |last1=Dannen |first1=Gene |date=March 2001 |title=Szilard's Inventions Patently Halted |url=https://physicstoday.scitation.org/doi/10.1063/1.1366083?journalCode=pto&ver=pdfcov |journal=Physics Today |volume=54 |issue=3 |pages=102–104 |bibcode=2001PhT....54c.102D |doi=10.1063/1.1366083 |access-date=31 January 2022}}</ref> In these applications, Szilárd became the first person to discuss the resonance condition for a circular accelerating apparatus. However, neither Steenbeck's ideas nor Szilard's patent applications were ever published and therefore did not contribute to the development of the cyclotron.<ref>{{cite journal |last1=Telegdi |first1=Valentine L. |date=October 2000 |title=Szilard as Inventor: Accelerators and More |journal=Physics Today |volume=53 |issue=10 |pages=25–28 |bibcode=2000PhT....53j..25T |doi=10.1063/1.1325189 |access-date=|doi-access=free}}</ref> 

Several months later, in the early summer of 1929, Ernest Lawrence independently conceived the cyclotron concept after reading a paper by [[Rolf Widerøe]] describing a drift tube accelerator.<ref>{{cite journal |last=Widerøe |first=R. |year=1928 |title=Ueber Ein Neues Prinzip Zur Herstellung Hoher Spannungen |journal=[[Archiv für Elektronik und Übertragungstechnik]] |language=de |volume=21 |issue=4 |pages=387–406 |doi=10.1007/BF01656341 |s2cid=109942448}}</ref><ref>{{cite web |date=8 December 2008 |title=Breaking Through: A Century of Physics at Berkeley 1886–1968 2. The Cyclotron. |url=http://bancroft.berkeley.edu/Exhibits/physics/bigscience02.html |url-status=dead |archive-url=https://web.archive.org/web/20120527183442/http://bancroft.berkeley.edu/Exhibits/physics/bigscience02.html |archive-date=2012-05-27 |publisher=[[Bancroft Library]], [[UC Berkeley]]}}</ref><ref>{{cite conference |last1=Livingston |first1=M. Stanley |date=19–22 August 1975 |title=The History of the Cyclotron |url=https://accelconf.web.cern.ch/c75/papers/j-01.pdf |location=Zurich, Switzerland |pages=635–638 |book-title=Proceedings of the 7th International Conference on Cyclotrons and their Applications}}</ref> He published a paper in ''[[Science (journal)|Science]]'' in 1930 (the first published description of the cyclotron concept), after a student of his built a crude model in April of that year.<ref>{{cite journal |author1=E. O. Lawrence |author2=N. E. Edlefsen |year=1930 |title=On the Production of High Speed Protons |journal=Science |volume=72 |issue=1867 |pages=376–377 |doi=10.1126/science.72.1867.372 |pmid=17808988 |s2cid=56202243}}</ref> He patented the device in 1932.<ref name="Lawrence2">{{cite journal |last1=Lawrence |first1=Earnest O. |last2=Livingston |first2=M. Stanley |date=April 1, 1932 |title=The Production of High Speed Light Ions Without the Use of High Voltages |journal=Physical Review |publisher=American Physical Society |volume=40 |issue=1 |pages=19–35 |bibcode=1932PhRv...40...19L |doi=10.1103/PhysRev.40.19 |doi-access=free}}</ref><ref name="Physics2">{{cite book |last1=Alonso |first1=M. |url=https://archive.org/details/physics00alon |title=Physics |last2=Finn |first2=E. |publisher=[[Addison Wesley]] |year=1992 |isbn=978-0-201-56518-8 |url-access=registration}}</ref>

To construct the first such device, Lawrence used large electromagnets recycled from obsolete [[Arc converter|arc converters]] provided by the [[Federal Telegraph Company]].<ref>{{cite journal |last=Mann |first=F. J. |date=December 1946 |title=Federal Telephone and Radio Corporation, A Historical Review: 1909–1946 |journal=Electrical Communication |volume=23 |issue=4 |pages=397–398}}</ref> He was assisted by a graduate student, [[M. Stanley Livingston]]. Their first working cyclotron became operational on January 2, 1931.  This machine had a diameter of {{convert|4.5|in|cm}}, and accelerated protons to an energy up to 80&nbsp;[[Electronvolt|keV]].<ref name="aipexhibit2">{{cite web |title=The First Cyclotrons |url=https://history.aip.org/exhibits/lawrence/first.htm |access-date=7 June 2022 |publisher=[[American Institute of Physics]]}}</ref><ref name="c609">{{cite web |title=The Centennial of The University of California, 1868-1968 |url=https://oac.cdlib.org/view?docId=hb4v19n9zb;NAAN=13030&doc.view=frames&chunk.id=div00569&toc.depth=1&toc.id=div00015&brand=calisphere |access-date=2024-12-26 |website=Online Archive of California}}</ref>

At the Radiation Laboratory on the campus of the [[University of California, Berkeley]] (now the [[Lawrence Berkeley National Laboratory]]), Lawrence and his collaborators went on to construct a series of cyclotrons which were the most powerful accelerators in the world at the time; a {{convert|27|in|cm|0|abbr=on}} 4.8&nbsp;MeV machine (1932), a {{convert|37|in|cm|0|abbr=on}} 8&nbsp;MeV machine (1937), and a {{convert|60|in|cm|0|abbr=on}} 16&nbsp;MeV machine (1939). Lawrence received the 1939 [[Nobel Prize in Physics]] for the invention and development of the cyclotron and for results obtained with it.<ref>{{cite web |title=The Nobel Prize in Physics 1939 |url=http://nobelprize.org/nobel_prizes/physics/laureates/1939/index.html |url-status=live |archive-url=https://web.archive.org/web/20081024052532/http://nobelprize.org/nobel_prizes/physics/laureates/1939/index.html |archive-date=24 October 2008 |access-date=9 October 2008 |publisher=Nobel Foundation}}</ref>

The first European cyclotron was constructed in 1934 in the [[Soviet Union]] by Mikhail Alekseevich Eremeev, at the [[Leningrad Physico-Technical Institute]]. It was a small design based a prototype by Lawrence, with a 28 cm diameter capable of achieving 530 keV proton energies. Research quickly refocused around the construction of a larger MeV-level cyclotron, in the physics department of the [[V.G. Khlopin Radium Institute]] in Leningrad, headed by {{Interlanguage link multi|Vitaly Khlopin|ru|Хлопин, Виталий Григорьевич|preserve=1}}. This instrument was first proposed in 1932 by [[George Gamow]] and {{Interlanguage link multi|Lev Mysovskii|ru|Мысовский, Лев Владимирович|preserve=1}} and was installed and became operative in March 1937 at 100 cm (39 in) diameter and 3.2 MeV proton energies.<ref>{{cite journal |last=Emelyanov |first=V. S. |year=1971 |title=Nuclear Energy in the Soviet Union |url=https://books.google.com/books?id=jQsAAAAAMBAJ&pg=PA38 |journal=[[Bulletin of the Atomic Scientists]] |volume=27 |issue=9 |pages=39 |bibcode=1971BuAtS..27i..38E |doi=10.1080/00963402.1971.11455411 |quote=State Institute of Radium, founded in 1922, now known as V. G. Khlopin Radium Institute|url-access=subscription }}</ref><ref name="h373">{{cite web |title=Радиевый институт. Хроника событий. История коллекций. |url=https://elib.biblioatom.ru/text/radievyy-institut_2023/p155/?hl=%D0%BC%D0%B0%D1%80%D1%82%201937 |access-date=2024-12-27 |website=Электронная библиотека /// История Росатома |language=ru}}</ref><ref name="chronology">V. G. Khlopin Radium Institute. [http://www.khlopin.ru/english/hronology.php Chronology] {{Webarchive|url=https://web.archive.org/web/20110426033000/http://www.khlopin.ru/english/hronology.php |date=2011-04-26 }}. Retrieved 25 February 2012.</ref>

The first Asian cyclotron was constructed at the [[Riken]] laboratory in Tokyo, by a team including [[Yoshio Nishina]], Sukeo Watanabe, Tameichi Yasaki, and Ryokichi Sagane. Yasaki and Sagane had been sent to [[Berkeley Radiation Laboratory]] to work with Lawrence. The device had a 26 in diameter and the first beam was produced on April 2, 1937, at 2.9 MeV deuteron energies.<ref name="h349">{{cite journal |last=KIM |first=DONG-WON |date=2006-03-01 |title=Yoshio Nishina and two cyclotrons |journal=Historical Studies in the Physical and Biological Sciences |publisher=University of California Press |volume=36 |issue=2 |pages=243–273 |doi=10.1525/hsps.2006.36.2.243 |issn=0890-9997}}</ref><ref name="x344">{{cite web |date=2024-12-26 |title=Yoshio Nishina |url=https://ahf.nuclearmuseum.org/ahf/profile/yoshio-nishina/ |access-date=2024-12-26 |website=Nuclear Museum}}</ref>

=== During World War II ===
Cyclotrons played a key role in the [[Manhattan Project]]. The published 1940 discovery of [[neptunium]] and the withheld 1941 discovery of [[plutonium]] both used bombardment in the [[Berkeley Radiation Laboratory]]'s 60-inch cyclotron.<ref name="EL93">{{cite journal |author=Mcmillan, Edwin |last2=Abelson |first2=Philip |date=1940 |title=Radioactive Element 93 |journal=Physical Review |volume=57 |issue=12 |pages=1185–1186 |bibcode=1940PhRv...57.1185M |doi=10.1103/PhysRev.57.1185.2 |doi-access=free}}</ref><ref name="SeaborgStory">{{Cite web |last=Glenn T. Seaborg |date=September 1981 |title=The plutonium story |url=http://www.osti.gov/bridge/purl.cover.jsp?purl=/5808140-l5UMe1/ |url-status=live |archive-url=https://web.archive.org/web/20130516093638/http://www.osti.gov/bridge/purl.cover.jsp?purl=%2F5808140-l5UMe1%2F |archive-date=May 16, 2013 |access-date=March 16, 2022 |publisher=Lawrence Berkeley Laboratory, University of California |id=LBL-13492, DE82 004551}}</ref> Furthermore Lawrence invented the [[calutron]] (California University cyclotron){{efn|Note that although the name "calutron" is derived from that of the cyclotron, calutrons are not themselves cyclotrons, as the beam crosses the accelerating gap only once.}}, which was industrially developed at the [[Y-12 National Security Complex]] from 1942. This provided the bulk of the [[uranium enrichment]] process, taking [[low-enriched uranium]] (<5% uranium-235) from the [[S-50 (Manhattan Project)|S-50]] and [[K-25]] plants and electromagnetically separating isotopes up to 84.5% [[highly enriched uranium]] (HEU). This was the first production of HEU in history, and was shipped to Los Alamos and used in the [[Little Boy]] bomb [[Atomic bombings of Hiroshima and Nagasaki|dropped on Hiroshima]], and its precursor [[Aqueous homogeneous reactor|Water Boiler]] and [[Dragon critical assembly|Dragon]] test reactors.<ref name="m226">{{cite journal |last=Reed |first=Cameron |year=2011 |title=From Treasury Vault to the Manhattan Project |url=http://www.jstor.org/stable/25766759 |journal=American Scientist |publisher=Sigma Xi, The Scientific Research Society |volume=99 |issue=1 |pages=40–47 |doi=10.1511/2011.88.40 |issn=0003-0996 |jstor=25766759 |access-date=2024-12-21}}</ref>

In France, [[Frédéric Joliot-Curie]] constructed a large 7 MeV cyclotron at the [[Collège de France]] in Paris, achieving the first beam in March 1939. With the [[Nazi occupation of Paris]] in June 1940 and an incoming contingent of German scientists, Joliot ceased research into uranium fission, and obtained an understanding with his German former colleague [[Wolfgang Gentner]] that no research of military use would be carried out. In 1943 Gentner was recalled for weakness, and a new German contingent attempted to operate the cyclotron. However, it is likely that Joliot, a member of [[French Communist Party]] and in fact president of the [[National Front (French Resistance)|National Front]] resistance movement, sabotaged the cyclotron to prevent its use to the [[German nuclear program during World War II|Nazi German nuclear program]].<ref name="d249">{{cite book |last=Gablot |first=Ginette |chapter-url=https://link.springer.com/content/pdf/10.1007/978-3-7643-8933-8_5.pdf |title=The Physical Tourist |date=2009 |publisher=Birkhäuser Basel |isbn=978-3-7643-8932-1 |publication-place=Basel |pages=73–80 |chapter=A Parisian Walk along the Landmarks of the Discovery of Radioactivity |doi=10.1007/978-3-7643-8933-8_5 |access-date=2024-12-31 |doi-access=free}}</ref><ref name="l813">{{cite journal |date=1960 |title=Jean Frédéric Joliot, 1900-1958 |journal=Biographical Memoirs of Fellows of the Royal Society |volume=6 |pages=86–105 |doi=10.1098/rsbm.1960.0026 |issn=0080-4606}}</ref>

In [[Nazi Germany]], one cyclotron was built in [[Heidelberg]], under the supervision of [[Walther Bothe]] and [[Wolfgang Gentner]], with support from the [[Heereswaffenamt]]. At the end of 1938, Gentner was sent to [[University of California, Berkeley|Berkeley Radiation Laboratory]] and worked most closely with [[Emilio Segrè]] and [[Donald Cooksey]], returning before the start of the war.  Construction was slowed by the war and completed in January 1944, but difficulties in testing made it unusable until the war's end.<ref name="g387">{{cite book |last=Walker |first=Mark |title=German National Socialism and the Quest for Nuclear Power, 1939–49 |date=1989-12-14 |publisher=Cambridge University Press |isbn=978-0-521-36413-3 |page=134 |doi=10.1017/cbo9780511562976}}</ref><ref>{{cite web |author=Ulrich Schmidt-Rohr |title=Wolfgang Gentner 1906–1980 |url=http://www.physik.uni-frankfurt.de/paf/paf181.html |archive-url=https://web.archive.org/web/20070706153823/http://www.physik.uni-frankfurt.de/paf/paf181.html |archive-date=6 July 2007 |language=de}}</ref><ref>{{Cite book |last=Ball |first=Philip |author-link=Philip Ball |url=https://www.worldcat.org/oclc/855705703 |title=Serving the Reich: the Struggle for the Soul of Physics Under Hitler |date=2013 |publisher=The Bodley Head |isbn=978-1-84792-248-9 |location=London |pages=190 |oclc=855705703}}</ref>

In Japan, the large Riken cyclotron was used to bombard uranium processed in their [[Karl Clusius|Clusius]] tube [[gaseous diffusion]] device. The experiment indicated that no enrichment of the uranium-235 content had occurred.<ref name="y213">{{cite journal |last1=Grunden |first1=Walter E. |last2=Walker |first2=Mark |last3=Yamazaki |first3=Masakatsu |date=2005 |title=Wartime Nuclear Weapons Research in Germany and Japan |journal=Osiris |volume=20 |pages=107–130 |doi=10.1086/649415 |pmid=20503760 |issn=0369-7827}}</ref> Following the [[occupation of Japan]], American forces, fearing continuation of the [[Japanese nuclear weapons program]], dissembled the Riken laboratory's cyclotron and dumped it in [[Tokyo Bay]]. During the disassembly, Yoshio Nishina begged otherwise, saying "This is ten years of my life ... It has nothing to do with bombs." Secretary of War [[Robert P. Patterson]] later admitted the decision was a mistake.<ref name="h349" />

=== Post-war ===
By the late 1930s it had become clear that there was a practical limit on the beam energy that could be achieved with the traditional cyclotron design, due to the effects of [[special relativity]].<ref>{{cite journal |last1=Bethe |first1=H. A. |last2=Rose |first2=M. E. |date=15 December 1937 |title=The Maximum Energy Obtainable from the Cyclotron |journal=Physical Review |volume=52 |issue=12 |pages=1254–1255 |bibcode=1937PhRv...52.1254B |doi=10.1103/PhysRev.52.1254.2}}</ref>  As particles reach relativistic speeds, their effective mass increases, which causes the resonant frequency for a given magnetic field to change.  To address this issue and reach higher beam energies using cyclotrons, two primary approaches were taken, [[Synchrocyclotron|synchrocyclotrons]] (which hold the magnetic field constant, but decrease the accelerating frequency) and isochronous cyclotrons (which hold the accelerating frequency constant, but alter the magnetic field).<ref name="craddock2">{{cite conference |last=Craddock |first=M.K. |date=September 10, 2010 |title=Eighty Years of Cyclotrons |url=http://accelconf.web.cern.ch/Cyclotrons2010/papers/mom1cio02.pdf |access-date=January 24, 2022 |book-title=Proceedings of Cyclotrons 2010 |place=Lanzhou, China}}</ref>

Lawrence's team built one of the first synchrocyclotrons in 1946. This {{convert|184|in|m|abbr=on}} machine eventually achieved a maximum beam energy of 350&nbsp;MeV for protons. However, synchrocyclotrons suffer from low beam intensities (<&nbsp;1&nbsp;μA), and must be operated in a "pulsed" mode, further decreasing the available total beam. As such, they were quickly overtaken in popularity by isochronous cyclotrons.{{r|craddock}}

The first isochronous cyclotron (other than classified prototypes) was built by F. Heyn and K.T. Khoe in Delft, the Netherlands, in 1956.<ref name="heyn2">{{cite journal |last1=Heyn |first1=F. |last2=Khoe |first2=Kong Tat |date=1958 |title=Operation of a Radial Sector Fixed-Frequency Proton Cyclotron |journal=Review of Scientific Instruments |volume=29 |issue=7 |page=662 |bibcode=1958RScI...29..662H |doi=10.1063/1.1716293}}</ref> Early isochronous cyclotrons were limited to energies of ~50&nbsp;MeV per nucleon, but as manufacturing and design techniques gradually improved, the construction of "spiral-sector" cyclotrons allowed the acceleration and control of more powerful beams. Later developments included the use of more compact and power-efficient [[superconducting magnets]] and the separation of the magnets into discrete sectors, as opposed to a single large magnet.{{r|craddock}}